Effects of Neutron Irradiation on Ni-Based Alloys: A Comparative Study Between PM-HIP and Forging

Effects of Neutron Irradiation on Ni-Based Alloys: A Comparative Study Between PM-HIP and Forging | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Effects of Neutron Irradiation on Ni-Based Alloys: A Comparative Study Between PM-HIP and Forging Ronit Roy, Soumita Mondal, Caleb Clement, Noah Pearlstein, Yu Lu, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8157703/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract This work presents a systematic and comprehensive investigation of neutron irradiation effects on Ni-based alloys manufactured by powder metallurgy with hot isostatic pressing (PM-HIP) compared to their conventional forged counterparts. PM-HIP is a leading candidate to replace forging as a manufacturing method for structural components in future nuclear reactors due to its more homogeneous microstructures and superior mechanical properties. However, such components can be exposed to elevated temperature irradiation in service, which will significantly alter material performance. Understanding PM-HIP material performance as compared to conventional forgings under realistic reactor operating conditions is therefore essential for certification and deployment. In this study, Ni-based Alloys 625 and 690 are investigated under neutron irradiation at target damage levels of ~ 1 and ~ 3 dpa, allowing for direct comparisons between PM-HIP manufacturing and forging. Uniaxial tensile tests evaluate the irradiation-induced changes in mechanical behaviour, while the irradiation-induced microstructural changes are investigated using transmission electron microscopy and atom probe tomography. Overall, PM-HIP Alloy 625 presents superior mechanical properties (e.g., less irradiation hardening, smaller reduction in ductility) compared to forged Alloy 625 under irradiation. This is primarily attributed to the fact that PM-HIP Alloy 625 has an order-of-magnitude lower void population than that observed in the forged counterpart at all damage levels due to its lower initial dislocation density. On the other hand, minimal differences in irradiation-induced microstructures are observed between PM-HIP and forged Alloy 690, resulting in suppressed differences in mechanical properties between them at corresponding damage levels. These findings consistently demonstrate comparable or greater irradiation tolerance in PM-HIP Alloy 625 and 690 than in their forged counterparts, providing crucial data to support the qualification of PM-HIP manufacturing of Ni-based alloys for future generation nuclear structural components. Physical sciences/Engineering Physical sciences/Materials science Alloy 625 Alloy 690 Powder Metallurgy Hot Isostatic Pressing (PM-HIP) Neutron irradiation Mechanical behaviour Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction The structural components of nuclear reactors are exposed to extreme conditions, such as irradiation, high temperature, and highly corrosive environments during their service life [ 1 – 6 ]. Hence, the integrity and stability of structural components are key to ensuring safe and economical operation of nuclear reactors. Traditionally, these components have been manufactured by forging or casting methods [ 7 , 8 ]. However, these manufacturing methods often result in casting or forging defects, such as pinholes, blowholes, cold shuts and hot cracking [ 9 , 10 ]. Moreover, near-net (component) shape productions are extremely challenging with the aforementioned techniques; thus, extensive post-processing techniques, such as machining and welding, are often required [ 9 , 11 , 12 ]. This can generate weak points in the components and make inspection and quality control challenging, especially during operations. Recent advancements in manufacturing methods have overcome these problems, alongside providing enhanced microstructure and mechanical properties with a more economical production. Thus, these new manufacturing methods are being considered for future nuclear reactor structural components [ 13 ]. Powder metallurgy with hot isostatic pressing (PM-HIP) is a powder-based advanced manufacturing technique that takes advantage of solid-state diffusion. During PM-HIP, gas atomized metallic powders are consolidated under 100 MPa to 150 MPa isostatic pressure at temperatures typically above 70% of the melting temperature ( \(\:\ge\:0.7{T}_{m}\) ) of the material [ 14 ]. Compared with traditional casting or forging, PM-HIP components are fabricated in a near-net shape, minimizing the post-processing steps and reducing the cost. Moreover, PM-HIP components offer greater density, chemical homogeneity, equiaxed grain structure, fewer defects and enhanced mechanical properties, compared to their cast or forged counterparts [ 15 – 18 ]. In recent years, PM-HIP components of ferritic, austenitic stainless steels, and Ni-alloys have been certified for non-nuclear applications [ 8 , 12 , 19 ]. Most recently, the PM-HIP fabrication technique has also been qualified to manufacture 316L stainless steel components for secondary circuits of nuclear reactors [ 19 ]. Nowadays, the nuclear industry has shown utmost interest in certification of PM-HIP components for use on the primary circuit [ 9 , 10 ]. However, such certification requires an understanding of the performance of PM-HIP components under irradiation [ 10 ], which is the primary objective of the present study. Despite the broad applications for PM-HIP manufacturing in nuclear energy systems, work on understanding the irradiation response of PM-HIP materials is limited [ 19 – 23 ]. Clement et al. [ 7 , 8 ] presented a systematic comparison of irradiation response between PM-HIP and traditionally manufactured Alloy 625 under both ion and neutron irradiation. It was reported that the PM-HIP alloy exhibits superior mechanical behaviour, such as ductility and tensile strength, compared to its forged counterparts. A similar comparison between PM-HIP and forged low-carbon steel SA508 was reported by Jiang et al. [ 19 ]. After irradiation, PM-HIP SA508 has a similar estimated toughness but shows superior ductility at maximum load-bearing capacity than the forging. Work by Wharry et al. [ 24 ] also reported lower irradiation hardening and greater ductility in PM-HIP manufactured 316L stainless steel than its cast counterpart. Subsequently, Chatterjee et al. [ 25 ] explained that this superior PM-HIP ductility was associated with pseudoelasticity that occurs uniquely in irradiated PM-HIP 316L. Recent work on PM-HIP Grade 91 steel also reported superior mechanical performance over its cast counterpart [ 26 ]. Overall, these aforementioned superior mechanical behaviors of PM-HIP compared to cast or forged materials, which include ferritic and austenitic steels as well as Ni-based alloys, can generally be associated with greater resistance to the formation of irradiation-induced extended defects such as loops, cavities, and nanoprecipitates [ 24 ]. These studies show that PM-HIP components exhibit more promising performance compared to traditionally manufactured components under irradiation, which facilitates the potential use of these components in the nuclear industry. However, these studies have probed only low irradiation doses ~ 1 displacement per atom (dpa), leaving opportunity and need for further studies at higher doses to understand the irradiation response of PM-HIP components over their expected service life. In the current study, we selected two Ni-based alloys, i.e., Alloys 625 and 690, since this alloy class is a leading candidate for internal and structural components in future generation reactors. In the current fleet of light-water reactors, Ni-based alloys are mostly used in heat exchangers and steam generators on the secondary circuit, owing to their high temperature performance and superior corrosion resistance [ 27 – 29 ]. But as these components are not exposed to direct and significant irradiation, studies on the irradiation response of Ni-based alloys are limited. However, in recent years, these alloys have been considered as potential structural material for advanced Gen IV reactors, such as molten salt reactors (MSR), small modular reactors (SMR) and gas-cooled very high temperature reactors (VHTR) [ 30 – 32 ]. In such reactor operating environments, these components are expected to operate at temperatures as high as 700°C and accumulate doses up to 100 dpa over their service life [ 7 , 8 ]. Moreover, these Ni-based alloys are susceptible to precipitate hardening and embrittlement (related to the formation of embrittling phases) over time under non-irradiated environments [ 33 – 35 ]. The rate of formation of such precipitate and embrittling phases is further enhanced under exposure to irradiation [ 1 , 36 , 37 ]. Hence, understanding the irradiation response of these Ni-based alloys coupled with the PM-HIP manufacturing process is particularly important for identifying and qualifying an advanced, economical, and modular heavy component manufacturing supply chain for Gen IV reactors. In the present study, we characterize the irradiation response of Alloys 625 and 690 under neutron irradiation and provide a one-to-one comparison between the PM-HIP and forged manufacturing routes at two different damage levels. For this purpose, transmission electron microscopy (TEM) discs and threaded tensile bars are neutron irradiated up to 1 dpa and 3 dpa damage levels at ~ 400°C target temperature. The mechanical properties of the tensile specimens are evaluated following American Society for Mechanical Engineers (ASME) E8 tensile tests, and the irradiation-induced microstructures are characterized using a combination of scanning transmission electron microscopy (S/TEM) and atom probe tomography (APT). Further, the correlation between the irradiated microstructure and the estimated mechanical properties is established in terms of initial sink strength. The current observations contribute to a wider understanding of the irradiation response of Ni-based alloys in combination with PM-HIP manufacturing. Results Tensile Tests The engineering stress-strain curves obtained from the uniaxial tensile tests for PM-HIP and forged specimens for Alloys 625 and 690 are presented in Fig. 1 . The yield strength of each specimen is calculated with a 0.2% strain offset. The details of tensile specimen irradiation conditions, yield strength (YS), ultimate tensile strength (UTS), uniform elongation (UE), total elongation (TE), and irradiation hardening are summarized in Table 1 . We note that the non-irradiated and 1 dpa irradiated data for Alloy 625 presented here have been previously reported in ref. [ 8 ]. However, to maintain continuity and for completeness, we include those observations here. Table 1 Details of irradiation and corresponding mechanical properties obtained from uniaxial tensile tests Alloy Fabrication As-Run Dose (dpa) As-Run Average Temperature (ºC) Load at Yield (kN) Max. Load (kN) YS (Pa) UTS (MPa) UE (%) TE (%) Irradiation Hardening (MPa) 625 PM-HIP 0 – 14.6 24.3 462.2 768.4 45.5 52.3 – 0.53 321 16.8 31.8 529 1003.8 39.9 45.9 66.8 0.73 339 17.3 32.0 546.9 1010.6 37.2 39.2 84.7 3.69 367 26.3 35.0 830.0 1104.9 27.7 29.1 367.8 3.93 384 21.0 32.8 664.2 1034.2 13.7 13.7 202.0 Forged 0 – 14.4 27.3 455.8 861.9 49.4 56.0 – 0.52 338 – – 601.9 964.2 38.5 40.4 146.1 0.71 355 22.0 34,4 694.4 1087.3 35.7 36.0 238.6 3.84 380 22.6 30.0 714.3 948.0 28.1 30.3 258.5 690 PM-HIP 0 – 91.9 21.4 290.2 675.2 43.9 54.1 – 0.86 368 15.9 25.0 501.5 790.2 36.4 44.3 211.3 0.99 342 16.2 25.0 510.8 788.3 35.0 42.6 220.6 2.82 378 22.6 28.0 714.2 884.4 23.1 29.0 424.0 3.29 378 23.1 28.4 728.0 897.2 22.9 29.5 437.8 Forged 0 – 7.9 20.2 248.1 636.9 50.7 61.7 – 0.86 335 15.0 25.0 472.7 790.0 51.1 60.7 224.6 0.99 358 16.5 25.1 521.1 791.0 40.9 48.1 273.0 3.12 373 19.9 25.7 626.8 809.9 20.7 28.0 378.7 3.52 385 23.3 26.1 736.1 825.5 14.8 22.3 488.0 The non-irradiated PM-HIP and forged Alloy 625 exhibit identical YS. However, a decrease in UTS is observed in the PM-HIP Alloy 625 compared to the forged counterpart. For Alloy 625, similar observations have been reported by Guillen et al. [ 38 ]. The elongation (UE and TE) for both PM-HIP and forged Alloy 625 is nearly similar, with a slightly lower elongation observed in the PM-HIP material. Similar values have been previously reported [ 39 , 40 ]. Unlike Alloy 625, a small increase in both YS and UTS is observed in non-irradiated PM-HIP Alloy 690 compared to its forged counterpart. However, elongation comparison between PM-HIP and forged Alloys 690 is nearly identical to what was observed for Alloy 625, i.e., the forged Alloy 690 exhibits a slightly higher elongation than PM-HIP. For Alloy 625, the increase of YS due to irradiation in PM-HIP material is considerably smaller than that observed in the forged material at ~ 0.5 dpa damage, resulting in lower irradiation hardening. Identical behaviour is also seen in the PM-HIP and forged Alloy 625 materials, irradiated at ~ 0.7 dpa and ~ 3.85 dpa. However, we note that one of the PM-HIP datasets, irradiated at 3.69 dpa, exhibits contradictory behaviour, with a very high increase of YS. Since no such behaviour has been previously reported for PM-HIP Alloy 625, this specimen may be an outlier of the experimental set. In addition, we acknowledge that having only a single tensile specimen at a given neutron irradiation condition inherently limits statistical confidence and repeatability, but this is an inherent limitation of the availability of irradiated material for testing. Regarding ductility, both PM-HIP Alloy 625 specimens irradiated at 0.53 dpa and 0.73 dpa exhibit a higher TE than the forged specimens. On the other hand, the PM-HIP Alloy 625 specimen irradiated at 3.69 dpa exhibits slightly lower TE than the forged specimen irradiated at 3.84 dpa. Since the PM-HIP Alloy 625 specimen irradiated at 3.93 dpa fractured prematurely, it is not considered in the reduction of ductility estimates. Overall, these results suggest that PM-HIP Alloy 625 exhibits similar or greater resistance to irradiation-induced hardening and ductility reduction compared to the forged counterpart. For Alloy 690, the PM-HIP specimens irradiated at 0.86 dpa and 0.99 dpa exhibit a nearly identical or an increase in YS compared to the forged specimens. Similar characteristics are also observed among the PM-HIP and forged Alloy 690 specimens at higher damage levels. Regarding ductility, PM-HIP Alloy 690 specimens show a lower TE at 0.86 dpa and 0.99 dpa than their forged counterparts. But the difference between PM-HIP and forged Alloy 690 diminishes as the damage level increases, as the initial loss of ductility in PM-HIP alloys levels off with saturation of defect structures at higher damage levels. These observations suggest the PM-HIP and forged Alloy 690 exhibit nearly identical mechanical responses under irradiation. To further investigate the tensile behaviour, the fracture surface images are collected, as shown in Fig. 2 . Due to radioactive specimen handling limitations, fractography is conducted only on Alloy 625, as we found greater differences in the tensile behaviour between PM-HIP and forged Alloy 625 compared to Alloy 690. At ~ 1 dpa, both PM-HIP and forged Alloy 625 specimens show evidence of cup and cone fracture with a significant number of dimples, resembling a ductile fracture mode. With increasing damage level, the fracture surfaces resemble a more brittle fracture mode with significantly fewer dimples for both PM-HIP and forged Alloy 625. However, no notable differences in fracture surface morphology between PM-HIP and forged Alloy 625 are apparent at either damage level. Irradiation-Induced Microstructure Upon exposure to neutron irradiation, face-centred cubic (FCC) materials undergo microstructural changes, such as formation of dislocation loops, voids, and stacking fault tetrahedra (SFT). Moreover, the size and density of these features are also influenced by the fluence and flux of the irradiation. The forthcoming results will present these microstructural changes depending on alloys, irradiation doses and temperatures. The distribution of irradiation-induced voids in both PM-HIP and forged alloys is shown in Fig. 3 . For both Alloys 625 and 690, a relatively homogenous spatial distribution of voids can be observed in each specimen. However, the average size and number density of the voids differ based on the Alloy and respective damage level. The details of the average void size and number density are quantified and provided in Table 2 and are plotted in Fig. 4 . The average void size observed in the PM-HIP and forged Alloy 625 is statistically identical at each damage level, ~ 2 nm. Although the average void size tends to decrease slightly with increasing damage levels (and also irradiation temperature) in both PM-HIP and forged Alloy 625, the changes fall within the standard error. These trends differ from typical reports in which the void size tends to increase with damage level either without bound [ 1 ] or until saturation [ 41 ]. Apart from that, PM-HIP Alloy 625 exhibits significantly lower void number density than its forged counterpart at both damage levels, i.e., \(\:\sim0.9\times\:{10}^{21}\:{m}^{-3}\) in PM-HIP compared to \(\:\sim3.6\times\:{10}^{21}\:{m}^{-3}\) in forged Alloy 625. In addition, the void number density in both PM-HIP and forged Alloy 625 increases by about an order of magnitude from 1 to 3 dpa. Table 2 Summary of irradiation-induced microstructure evolution with DBH model estimated irradiation hardening for each type of defect. Alloy Fabrica-tion As-Run Dose (dpa) As-Run Average Temperature (ºC) Dislocation loops Voids SFTs Clusters Total \(\:{\text{σ}}_{\text{sy}}\:\) (MPa) Measured \(\:{\text{σ}}_{\text{sy}}\:\) (MPa) \(\:\text{N}\:({10}^{21}\:{m}^{-3}\) ) d (nm) \(\:{\text{σ}}_{\text{sy}}\:\) (MPa) \(\:\text{N}\:({10}^{21}\:{m}^{-3}\) ) d (nm) \(\:{\text{σ}}_{\text{sy}}\:\) (MPa) \(\:\text{N}\:({10}^{21}\:{m}^{-3}\) ) d (nm) \(\:{\text{σ}}_{\text{sy}}\:\) (MPa) \(\:\text{N}\:({10}^{21}\:{m}^{-3}\) ) d (nm) \(\:{\text{σ}}_{\text{sy}}\:\) (MPa) 625 PM-HIP 1.05 385 14.1 ± 0.41 4.8 ± 1.83 75.92 ± 0.97 0.90 ± 0.32 2.41 ± 0.57 45.16 ± 8.91 – – – 39.0 ± 4.5 7.13 ± 1.48 30.8 ± 4.8 151.9 ± 14.64 84.7 Forged 1.06 385 11 ± 0.24 8.11 ± 3.81 87.15 ± 0.93 3.59 ± 1.54 2.22 ± 0.30 86.89 ± 7.44 – – – – – – 174.0 ± 8.36 146.1 PM-HIP 4.27 398 19.7 ± 4.74 11.13 ± 5.25 136.62 ± 3.11 8.22 ± 4.65 1.71 ± 1.15 115.43 ± 18.93 0.28 ± 0.06 9.03 ± 0.79 14.73 ± 0.38 57.4 ± 5.3 8.74 ± 1.85 41.3 ± 5.8 308.1 ± 28.21 202.05 Forged 4.2 398 9.14 ± 0.85 17.78 ± 7.95 117.63 ± 1.88 37.86 ± 3.60 1.51 ± 0.55 232.53 ± 5.74 1.01 ± 0.29 11.58 ± 0.59 31.55 ± 0.77 – – – 381.7 ± 8.39 258.52 690 PM-HIP 1.09 388 6.16 ± 0.31 14.42 ± 5.74 84.75 ± 1.3 1.67 ± 0.17 3.72 ± 1.34 74.57 ± 5.86 – – – – – – 159.3 ± 7.16 211.3 Forged 1.09 389 5.01 ± 0.58 11.66 ± 4.43 68.71 ± 1.94 2.02 ± 0.03 4.46 ± 2.00 89.98 ± 2.53 – – – – – – 158.7 ± 4.46 224.6 PM-HIP 4.14 398 8.43 ± 0.95 14.43 ± 7.44 99.14 ± 2.22 5.84 ± 0.42 2.58 ± 1.91 116.23 ± 7.10 0.46 ± 0.19 8.20 ± 0.83 17.44 ± 0.74 – – – 232.8 ± 10.07 424.04 Forged 4.11 398 7.28 ± 0.52 16.18 ± 8.89 97.57 ± 1.83 13.31 ± 1.33 1.90 ± 0.74 150.54 ± 6.06 0.48 ± 0.08 9.62 ± 0.50 19.34 ± 0.37 – – – 267.4 ± 8.27 378.71 In Alloy 690, the average void sizes in the PM-HIP and forged materials are statistically identical at each damage level. Additionally, the average void size tends to decrease with increasing damage level for both PM-HIP and forged Alloy 690, i.e., ~ 4 nm at 1 dpa to ~ 2 nm at 3 dpa. PM-HIP Alloy 690 has a lower void number density than the forged material at all damage levels (e.g., \(\:\sim1.7\times\:{10}^{21}\:{m}^{-3}\) in PM-HIP and \(\:\sim2.0\times\:{10}^{21}\:{m}^{-3}\) in forged at 1 dpa), although this difference between PM-HIP and forged void number densities is not as pronounced as that observed in Alloy 625. The void number densities in both PM-HIP and forged Alloy 690 increase with damage level, but this increase is not as significant as that observed in Alloy 625. The distribution of irradiation-induced dislocation loops and SFTs in both Alloys 625 and 690 is presented in Fig. 5 . The details of average size and number density for both dislocation loops and SFTs are quantified and provided in Table 2 , with a comparison of average dislocation loop size and density plotted in Fig. 6 . At both damage levels, the average size of dislocation loops in the PM-HIP Alloy 625 is smaller than that observed in the forged material, (e.g., ~ 5 nm in PM-HIP and ~ 8 nm in forged Alloy), though within error bars. An increase in average dislocation loop size in both PM-HIP and forged Alloy 625 is observed with increasing damage levels (e.g., from ~ 5 nm at 1 dpa to ~ 11 dpa at 3 dpa in PM-HIP Alloy), which is identical to previous reports based on Ni-based alloys [ 1 , 8 ]. Unlike the average size, the number density of dislocation loops is greater in the PM-HIP Alloy 625 than in the forged material at both damage levels. The density tends to increase in PM-HIP Alloy 625 between 1 and 3 dpa (i.e., from \(\:\sim14\times\:{10}^{21}\:{m}^{-3}\) at 1 dpa to \(\:\sim20\times\:{10}^{21}\:{m}^{-3}\) at 3 dpa). Similar observations have been previously reported in Ni-based alloys [ 1 , 8 ]. However, the dislocation loop number density decreases slightly in forged Alloy 625 between 1 and 3 dpa (i.e., from \(\:\sim11\times\:{10}^{21}\:{m}^{-3}\) at 1 dpa to \(\:\sim9\times\:{10}^{21}\:{m}^{-3}\) at 3 dpa). This likely results from loop coarsening, but may also be attributed to local heterogeneities and the small region of interest (ROI) sampled in a single TEM lamella. The average dislocation loop size among both PM-HIP and forged Alloy 690 is nearly identical (~ 14 nm) and does not follow specific trends like Alloy 625. No apparent increase in average dislocation loop size in both PM-HIP and forged Alloys 690 is observed with increasing damage level. In Alloy 690, a slightly higher number density of dislocation loops is observed in the PM-HIP compared to the forged material at both damage levels (e.g., \(\:\sim6.2\times\:{10}^{21}\:{m}^{-3}\) in PM-HIP \(\:\sim5.0\times\:{10}^{21}\:{m}^{-3}\) in forged at 1 dpa), although the difference is within standard error at the highest damage level. In addition, a slight increase in dislocation loop number density is observed in both PM-HIP and forged Alloy 690 with increasing damage levels (e.g., from \(\:\sim5.0\times\:{10}^{21}\:{m}^{-3}\) at 1 dpa to \(\:\sim7.3\times\:{10}^{21}\:{m}^{-3}\) at 3 dpa in the forged Alloy). SFTs are only found at the highest damage levels in Alloys 625 and 690. The average size of SFTs in both PM-HIP Alloys 625 and 690 tends to be slightly smaller than in the respective forged Alloys (e.g., ~ 9 nm and ~ 12 nm in PM-HIP and forged Alloy 625, respectively). In Alloy 625, the SFT number density is four times smaller in the PM-HIP than in the forged material. But in Alloy 690, the SFT number densities in both PM-HIP and forged Alloy 690 are identical, \(\:\sim0.5\times\:{10}^{21}\:{m}^{-3}\) . Nanoprecipitates Representative 3D reconstructions of the APT needles for both PM-HIP and forged Alloy 625 are presented in Fig. 7 . The chemical composition of APT needles is provided in Table 3 . Si nanoclustering, quantified in Table 2 , is only observed in the PM-HIP Alloy 625 at both damage levels. This is likely associated with the higher bulk Si concentration in the PM-HIP Alloy 625 than its forged counterpart. Another possibility is that the smaller dislocation loops in the PM-HIP Alloy 625 are weaker sinks, and thus limit the loss of Si to radiation-induced segregation (RIS) at dislocation loops and networks [ 37 , 42 ], consequently leaving more Si in the matrix to form clusters. The average size of Si clusters remains statistically unchanged with increasing dose level, although their number density increases with damage. Table 3 Chemical composition of Alloy 625 and Alloy 690 estimated from APT analysis (in %atoms). Alloy Fabrication C Si Mn P S Cr Ni Mo Ti Cu Al Co Fe Nb 625 PM-HIP 0.05 0.94 0.44 0.004 0.004 24.67 64.67 5.01 0.007 0.09 0.21 0.1 3.81 - Forged 0.05 0.41 0.45 0.011 0.007 25.93 62.37 4.68 0.38 - 0.11 - 3.71 1.89 690 PM-HIP 0.09 0.89 0.38 - 0.005 33.09 56.1 - - 0.009 0.04 - 9.4 - Forged 0.02 0.27 0.6 - 0.005 32.65 55.61 - 0.36 - 0.42 0.01 10.06 - The absence of Si clusters in the forged Alloy 625 is surprising, since Clement et al. find Si clusters in forged Alloy 625 even at lower damage levels, i.e. ~0.5 dpa to 0.7 dpa [ 8 ]. Evidence of Si clusters in traditionally manufactured Alloy 625 under both ion and proton irradiation is also reported by Yu and Marquis [ 37 , 42 ]. However, in the latter work, Si clusters forming during 1.5 dpa Ni + ion irradiation are significantly smaller than those forming during 11 dpa proton irradiation. Despite the characteristic differences in the damage cascade morphologies and efficiencies generated by proton compared to heavy ion irradiation, these works from Yu and Marquis show that the damage level strongly influences the size of Si clusters [ 37 , 42 ]. Damage levels in the present study are likely lower than may be required for the formation of prominent Si clusters in the forged Alloy 625 under neutron irradiation. Additionally, the stronger RIS at larger dislocation loops (i.e., stronger sinks) in the forged Alloy 625 delays the Si cluster formation in the matrix. However, small coalescences of Si atoms are observed in the forged Alloy 625 at ~ 3 dpa damage level, as shown in the inset of Fig. 7 (d). Note that all insets presented in Fig. 7 (d), (f) and (h) are taken from the edge, to minimize the visual effect of the needle thickness. These small Si atom coalescences are likely nucleation sites that will evolve into Si clusters at higher damage levels. No evidence of Si clusters is found in either PM-HIP or forged Alloy 690, despite having considerable bulk concentrations of Si, particularly in the PM-HIP Alloy 690. This can be attributed to the change in alloy composition between Alloy 625 and 690, specifically, the low fraction of secondary alloying elements in Alloy 690 may delay or prevent the formation of Si clusters. We note that Yu reported that Si clusters are found in conventionally manufactured Alloy 690 under proton irradiation, although the distribution is not homogeneous at all irradiation doses and temperatures [ 43 ]. In the current study, the dislocation loops formed in Alloy 690 (both PM-HIP and forged) are comparable to the forged Alloy 625 dislocation loop size, which possibly delays the formation of Si clusters by RIS at dislocation loops. Nonetheless, small coalescences of Si atoms are observed in both PM-HIP and forged Alloy 690 at ~ 3 dpa damage level, similar to forged Alloy 625. Discussion Dislocation Loop and Void Distribution To further explain the evolution of dislocation loop and void sizes among all specimens, the frequency distributions of the void and dislocation loop sizes with 95% confidence intervals for both fabrication methods of Alloys 625 and 690 are presented in Fig. 8 . The corresponding full width at half maximum (FWHM) values are estimated and provided in Table 4 . A higher FWHM value represents a broader size distribution, i.e., less uniform size distribution. Table 4 FWHM values of loop and void size distributions (in no. of bins). Dose (dpa) 1 dpa 3 dpa Alloy 625 690 625 690 Fabrication PM-HIP Forged PM-HIP Forged PM-HIP Forged PM-HIP Forged Loops 3 3 8 5 5 7 5 5 Voids 2 1 4 8 3 3 3 3 In Alloy 625, the dislocation loop size distribution tends to broaden and shift rightward with increasing damage level in both the forged and PM-HIP materials. However, the forged material exhibits a broader size distribution than the PM-HIP material, especially at higher damage levels. This, together with the decrease in the dislocation loop number density in forged Alloy 625 at higher damage levels, suggests that the loop population has reached saturation by ≤ 3 dpa. Meanwhile, in PM-HIP Alloy 625, loops continue to nucleate and grow between the damage levels studied, suggesting saturation has not yet occurred by 3 dpa. On the other hand, the dislocation loops formed in Alloy 690 exhibit a broad, non-uniform size distribution, with little difference between the PM-HIP and forged material. Although the dislocation loop size distributions broaden slightly with increasing damage level, the loop microstructure in Alloy 690 appears generally saturated by ~ 1 dpa. PM-HIP and forged Alloy 625 exhibit a uniform void size distribution at lower damage levels, which tends to broaden and also skew to smaller sizes at higher damage levels. This indicates that more voids are nucleating with increasing damage level, while the existing voids grow in size. This explains the relatively unchanged average void size and significant increase in void number density in both PM-HIP and forged Alloy 625 between 1 and 3 dpa. By contrast, the void size distributions in both PM-HIP and forged Alloy 690 are significantly broader, suggesting that non-uniformly sized voids are already present at lower damage levels. These void size distributions tend to skew leftward with increasing damage level, again demonstrating that more void nucleation is occurring than void growth in Alloy 690 between 1 and 3 dpa, similar to Alloy 625. In both Alloys 625 and 690, a greater number density of voids is observed in forged than in PM-HIP alloys. This can be correlated to the initial dislocation density in forged alloys [ 8 , 19 ]. As dislocations act as preferred sinks for interstitials, a higher initial dislocation density significantly reduces the possibility of recombination between vacancies and interstitials. This leads to more supersaturation of vacancies and promotes the formation of more voids in the forged alloys. In tandem, PM-HIP Alloy 625 has finer grain sizes than the forged material [ 44 ]. This will accelerate annihilation of both vacancies and interstitials at grain boundary sinks in the PM-HIP alloy, further reducing the population of vacancies in PM-HIP Alloy 625. Hence, the void number densities in PM-HIP Alloy 625 are generally the lowest amongst all materials and conditions studied. Finally, the difference in irradiation-induced defect population between Alloys 625 and 690 is attributed to the concentration of secondary elements in each alloy. Alloy 625 has a greater total concentration of secondary elements, including more Mo, but less Cr, than Alloy 690. These secondary alloying species exhibit different defect–solute interactions that can explain the dislocation loop and void microstructures. Li et al. [ 45 ] conducted He ion irradiation on pure Ni and binary Ni 0.9 Cr 0.1 and Ni 0.9 Mo 0.1 . They report that Mo has the most pronounced effect on increasing the number density of He bubbles (although those bubbles are smaller) due to its role in enhancing lattice stability and increasing migration barriers. This mechanism can explain the greater void number density in Mo-containing Alloy 625 than in Alloy 690. Li and coworkers [ 45 ] also find that Cr acts as a favorable trapping site to stabilize dislocation loops at sizes where the loops would have otherwise unfaulted. This can explain the larger loop sizes in Alloy 690, which has higher Cr content than Alloy 625. Similar defect–solute trapping effects, which lead to greater accumulation of irradiation-induced extended defects (e.g., loops and voids), are routinely observed at strongly undersized or strongly oversized substitutional solutes in steels [ 46 ], including B, Mn, and P in ferritic steels [ 46 , 47 ] or Cr in austenitic steel [ 48 ]. Irradiation Hardening Under exposure to irradiation, the yield strength tends to increase, known as irradiation hardening \(\:\left(\varDelta\:{\sigma\:}_{y}\right)\) . This results from the interaction between irradiation-induced defects and the movement of dislocations [ 19 , 49 ]. The Orowan dispersed barrier hardening (DBH) model is typically used to estimate \(\:\varDelta\:{\sigma\:}_{y}\) in a material by calculating the hardening contribution from each irradiation-induced defect types or sinks [ 1 ]. The DBH model can be expressed as, $$\:\varDelta\:{\sigma\:}_{yi}={\alpha\:}_{i}M\mu\:b\sqrt{{N}_{i}{d}_{i}}$$ 1 Where, \(\:{\alpha\:}_{i}\) is the strength factor of the \(\:{i}^{th}\) type sink or irradiation-induced defect [ 50 – 52 ]; \(\:M\) is the Taylor factor [ 53 ]; \(\:\mu\:\) and \(\:b\) are the shear modulus and Burgers vector, respectively [ 8 , 54 ]; and \(\:{N}_{i}\) and \(\:{d}_{i}\) are the number density and average size of the \(\:{i}^{th}\) type sink or irradiation-induced defect. In the present study, a total of four types of irradiation-induced defects are considered: dislocation loops, voids, SFTs and Si clusters. The details of the DBH model parameters used for the present study are listed in Table 5 . We note that the strength factors are selected for both Alloys 625 and 690, which provides a reasonable degree of correlation with the experimental observations. Among all sinks, voids exhibit the most significant \(\:\alpha\:\) . Si clusters are associated with the smallest \(\:\alpha\:\) among all sinks, contributing the least to irradiation hardening. Similar assumptions have been previously used [ 8 , 19 ]. The DBH calculated hardening contributions for a given defect type are provided alongside their number densities and average sizes in Table 2 . Notably, microstructural details used for the DBH model are estimated from the TEM specimens, whereas measured irradiation hardening is taken from tensile specimens. Although tensile and TEM specimens are irradiated to slightly different damage levels, this comparison provides a qualitative understanding of irradiation hardening and its correlation to different types of irradiation-induced defects. Table 5 Dispersed barrier hardening model parameters. Alloy 625 690 Burgers vector ( b ) 2.47 Å 2.47 Å Shear modulus ( µ ) 81.4 GPa 79.3 GPa Taylor factor ( M ) 3.06 3.06 Strength Factor ( α ) Loop 0.15 0.15 Void 0.5 0.5 SFT 0.15 0.15 Cluster 0.03 0.03 The irradiation hardening estimated from the tensile tests is compared with DBH model predictions and presented in Fig. 9 . For Alloy 625, the DBH model consistently overestimates the irradiation hardening compared to experimental measurements. This difference in hardening magnitude is associated with the higher damage level of the TEM specimens than the tensile specimens used in the current study. However, the DBH model accurately predicts that the PM-HIP material should exhibit less irradiation hardening than the forged counterpart at both damage levels, despite differences in the types of defects present. The DBH model also accurately predicts that both PM-HIP and forged Alloy 625 should exhibit an increase in irradiation hardening with increasing damage level. This is notable because of the significant increase in the hardening contribution from voids at the higher damage level. Previous reports have shown that voids result in significant irradiation hardening in irradiated Alloy 625 [ 8 ]. This is more evident in the forged Alloy 625, owing to the higher initial density of dislocations present in the material [ 7 , 8 ]. Dislocations act as a biased sink for interstitials, which leaves excess vacancies unable to recombine, thus promoting the nucleation of voids. Due to this, PM-HIP Alloy 625 tends to be more resistant to irradiation hardening than the forged material. In Alloy 690, the DBH model actually underestimates irradiation hardening compared to experimental measurements, despite higher damage levels in the TEM specimens than in the tensile bars. This is likely associated with the Ni-Cr ratio, which is closer to 2.0 in both PM-HIP and forged Alloy 690 than in Alloy 625 [ 55 , 56 ]. This Ni-Cr ratio favors the formation of Ni 2 Cr (MoPt 2 -type) ordered nanoprecipitates under irradiation, which could explain the higher irradiation hardening in the experimental dataset [ 55 , 56 ]. Also, both measured and DBH estimated irradiation hardening is nearly identical between PM-HIP and forged Alloy 690 at respective damage levels. An increase in irradiation hardening is observed in both the measured and the DBH estimates in both PM-HIP and forged Alloy 690 with increasing damage level. The rise in void number density increases irradiation hardening between the damage levels in both PM-HIP and forged Alloy 690. The contributing factors behind the irradiation hardening observed in PM-HIP and forged Alloys 625 and 690 are demonstrated using the DBH model. A reasonable degree of correspondence between the DBH model and the experimentally measured irradiation hardening values has been observed. Overall, the PM-HIP Alloy 625 exhibits superior mechanical response to the forged Alloy 625 at all damage levels. However, no significant differences in the irradiation-induced changes in mechanical behaviour have been observed between PM-HIP and forged Alloy 690 at any damage level. Summary Nuclear structural materials are subjected to various irradiation-induced damage, corrosion, and dimensional changes (swelling, irradiation creep, etc.), all of which can compromise mechanical integrity. As PM-HIP alloys are being considered as candidate materials for future generation reactor components, evaluating their performance under relevant reactor operating conditions is essential for certification and licensing for in-reactor use. The present study directly compares the response of PM-HIP and forged Ni-based Alloys 625 and 690 to neutron irradiation. For this purpose, both PM-HIP and forged materials are irradiated up to two different target damage levels, ~ 1 dpa (actual doses 0.53–1.09 dpa) and ~ 3 dpa (actual doses 2.82–4.27 dpa), at temperatures ~ 330–423 ºC. Further, the mechanical response and microstructural changes are compared to understand the irradiation-induced changes in the material behaviour. The following conclusions can be drawn: At both damage levels, a lower population of irradiation-induced voids and smaller irradiation-induced dislocation loops are observed in the PM-HIP Alloy 625 compared to those observed in forged Alloy 625. These microstructural differences result in superior irradiated mechanical properties in the PM-HIP Alloy 625 than the forged counterpart. The change in irradiation hardening between PM-HIP and forged Alloy 625 is associated with the density of initial dislocations, which act as biased sinks for interstitials. A higher initial dislocation density in forged Alloy 625 promotes supersaturation of vacancies and void formation, resulting in a more significant irradiation hardening than PM-HIP Alloy 625 at both damage levels. In Alloy 690, irradiation-induced microstructures are almost identical between PM-HIP and forged materials at both damage levels. The only statistically significant difference is a lower void density in PM-HIP than in forged Alloy 690 at ~ 3 dpa. Consequently, both PM-HIP and forged Alloy 690 exhibit nearly identical mechanical responses to both irradiation damage levels. This is associated with the lesser concentration of secondary elements in Alloy 690, which results in suppressed defect–solute interactions and formation of fewer dislocation loops and voids compared to Alloy 625, which minimizes the difference in irradiation hardening between PM-HIP and forged Alloy 690. Si nanoclusters are only observed in the PM-HIP Alloy 625. However, Si composition fluctuations, which are likely nucleation sites of Si clusters, are observed in forged Alloys 625 and 690, and in PM-HIP Alloy 690. The appearance of Si clustering in PM-HIP Alloy 625 is attributed to a combination of damage level, bulk Si concentration, and irradiation-induced dislocation loop size and density (RIS of Si at dislocation loops). The classical Orowan DBH model predictions of irradiation hardening capture the differences in mechanical behaviour between the PM-HIP and forged materials for both Alloys 625 and 690. However, Alloy 690 has a Ni-Cr ratio of ~ 2, which promotes the formation of Ni 2 Cr (MoPt 2 -type) ordered nanoprecipitates under irradiation; this explains why irradiation hardening in Alloy 690 exceeds the DBH predictions. This work consistently demonstrates comparable or greater irradiation tolerance in PM-HIP Alloy 625 and 690 than in their forged counterparts. Results herein offer key data that can support qualification of PM-HIP manufacturing for Ni-based structural alloys to be deployed in future nuclear energy systems. Methods Materials, Specimen Preparation, and Irradiation Specimens used in the current study were machined from Alloy 625 and 690 forged ingots and PM-HIP compacts supplied by the Electric Power Research Institute (EPRI). Alloys 625 and 690 PM-HIP compacts were fabricated by consolidating gas atomized alloy powders under 103 MPa pressure at 1149°C temperature for 4 hours. Further, the PM-HIP ingots were solution annealed at 1171 ± 14°C (for Alloy 625) or 1177 ± 14°C (for Alloy 690) for 2 hours, followed by water quenching [ 57 ]. Both forged Alloy 625 and 690 ingots were cast and hot rolled, followed by solution annealing at 1040°C for 2 hours and then kept in ambient cooling for 40 minutes. Further, two heat treatments were carried out on both forged ingots. First, a solution annealing was carried out at 1075°C for 30 minutes, followed by water quenching, then the ingots were thermally aged at 700°C for 15 hours, followed by air cooling. The chemical compositions of the PM-HIP and forged ingots for Alloys 625 and 690 were analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and are provided in Table 6 . Table 6 Chemical composition of Alloy 625 and Alloy 690 (in %wt.). Alloy Fabrication C Si Mn P S Cr Ni Mo Ti Cu Al Co Pb Fe Nb 625 PM-HIP 0.01 0.45 0.41 0.003 0.003 21.9 Bal 8.2 0.006 < 0.1 < 0.05 < 0.1 < 0.010 3.6 – Forged 0.01 0.2 0.42 0.006 0.004 23.7 Bal 7.6 0.31 – 0.02 – – 3.5 3.6 690 PM-HIP 0.019 0.45 0.37 – 0.003 30.9 Bal – – 0.01 < 0.02 – – 9.6 – Forged – 0.12 0.59 – 0.003 31.3 Bal – 0.31 – 0.26 – – 10.3 – TEM disc specimens and ASTM E8 standard threaded round tensile specimens were sectioned from PM-HIP compacts and forged ingots for Alloys 625 and 690 for characterization and mechanical testing. Electrical discharge machining (EDM) was used to cut the 3 mm diameter TEM discs from each material. Each disc was then mechanically polished using SiC paper up to 1200 grit to a final thickness of 250 ± 10 µm, then electropolished in a 10% perchloric acid in methanol solution at -40°C and 35 V for 20 s prior to irradiation. The threaded round tensile specimens were machined using computer numerical control (CNC) machining to 76.2 mm length and 6.35 mm gauge diameter with a surface roughness of 3.2 µm. The detailed drawings for the tensile and disc specimens are provided in Guillen et al. [ 57 ]. Once the tensile and disc specimens were prepared, the neutron irradiation was carried out at the Advanced Test Reactor (ATR) facility at Idaho National Laboratory (INL). Prior to insertion of specimens into the ATR, specimens were loaded into drop-in capsules to prevent contact with the reactor coolant. Each capsule was pressurized with a mixture of Ar and He to control the specimen temperature. As mentioned earlier, the target dose of specimens was set to 1 dpa and 3 dpa, and a target temperature of 400°C was selected. However, owing to the limited environmental control in a non-instrumented drop-in neutron irradiation capsule, the as-run doses experienced by the tensile specimens ranged between 0.53–0.99 dpa and 2.82–3.93 dpa for 1 dpa and 3 dpa target doses, respectively, and the as-run average temperature ranged between 330°C and 385°C. Similarly, the as-run doses experienced by the TEM discs ranged between 1.05–1.09 dpa and 4.11–4.27 dpa for 1 dpa and 3 dpa target doses, respectively, and the as-run average temperature ranged between 385°C and 398°C. Details of the capsule, assembly, irradiation experiment, as-run dose and temperature calculations are provided in ref. [ 57 ]. For microstructural and mechanical characterization in the present study, two irradiated disc specimens and two irradiated tensile bars for each material and were selected for testing and characterization [ 37 ]. Moreover, non-irradiated tensile and disc specimens from each material were also investigated as references. After irradiation, the capsules were disassembled at the Hot Fuel Examination Facility (HFEF) at INL. For microstructural characterization, the TEM discs were first decontaminated, then electropolished again with a 12.5% perchloric acid in ethanol solution at -17.5°C and 18 V. The tensile specimens were also decontaminated prior to testing. Mechanical Testing All uniaxial tensile tests (on both irradiated and non-irradiated specimens) were performed at the HFEF hot cell at INL using a 13M Instron load frame in accordance with the ASTM E8 standard. All uniaxial tensile tests were performed in an Ar environment at ambient temperature. For testing, an initial strain rate of \(\:8.78\times\:{10}^{-3}\:{s}^{-1}\) (corresponding displacement rate 0.279 mm/min) was used. After the specimens achieved 10% strain, the strain rate was increased to \(\:3.15\times\:{10}^{-2}\:{s}^{-1}\) (1.00 mm/min displacement rate), which was maintained until fracture. The details of uniaxial tensile testing are provided in ref. [ 58 ]. The resultant stress-strain curves from the uniaxial tensile tests were used to determine irradiation hardening \(\:\left(\varDelta\:{\sigma\:}_{y}\right)\) , as the increase in yield strength resulted from irradiation, i.e., \(\:\varDelta\:{\sigma\:}_{y}={\sigma\:}_{y,irr}-{\sigma\:}_{y,non-irr}\) , where \(\:{\sigma\:}_{y,irr},\:\:{\sigma\:}_{y,non-irr}\) are the yield strengths of the material before and after irradiation, respectively. After tensile tests, fractography on the tested specimens was carried out using a Tescan Lyra3 Scanning Electron Microscope (SEM) at HFEF. Microstructural Characterization To prepare TEM lamellae from the disc specimens, a focused ion beam (FIB)-enabled FEI Quanta 3D dual-beam SEM was used. A 2 × 20 × 3 µm Pt deposition was placed over a random region of interest for each TEM lamella. Next, trenches were milled on both sides of the Pt deposit, then the lamellae were cut free and lifted out. Then, the lamellae were transferred and mounted onto Cu TEM half-grids. Next, the lamellae were thinned using a gradually decreasing ion beam energy. At first, 30 kV Ga + ions at 1 nA current were used until a 150 µm thickness was achieved. Next, 5 kV Ga + ions at 0.26 nA current were used until the lamellae became electron transparent. Finally, the residual FIB damage and surface deposits were removed using 2 kV Ga + ions at 47 pA current. The same FIB-SEM was used to prepare the TEM lamellae and the APT specimens. To prepare APT specimens, lamellae were extracted from each specimen condition. They were cut into ~ 1 µm slices and Pt-welded to a Si post. Needle-shaped specimens having a radius < 100 nm were fabricated via an iterative top-down annular milling technique. A low-energy 5 kV polish and 2 kV final cleaning were successively used to eliminate damage associated with Ga penetration and/or FIB milling. An FEI Tecnai G2 F30 Scanning Transmission Electron Microscope (S/TEM) was used for the TEM analysis. Irradiation-induced dislocation loops were characterized following the down-zone bright field S/TEM technique [ 59 ]. At first, the specimens were loaded into a double-tilt holder and tilted to the \(\:⟨101⟩\) zone axis. Further, the bright field S/TEM mode was enabled for dislocation loop imaging. The bright field S/TEM mode relaxes the \(\:\stackrel{-}{g}\bullet\:\stackrel{-}{b}\) invisibility criterion and facilitates simultaneous imaging of all dislocation loops present in the material [ 60 , 61 ]. The Fresnel contrast through-focus technique was used to image irradiation-induced voids in bright field TEM mode. In addition, the thickness of each TEM lamella was estimated using the zero-loss peak in electron energy loss spectroscopy (EELS). All TEM and S/TEM data were analyzed using TEM instrument analysis software and Gatan Digital Micrograph. The APT analysis was conducted on a Cameca Local Electrode Atom Probe 4000X HR instrument operating in laser pulse mode at 45 K base temperature. A pulse repetition rate of 200 kHz and a focused laser beam energy of 60 pJ were selected for all APT analyses. 3D data reconstruction of the APT needles was carried out using Cameca IVAS 3.8.6 software. At least two needles from each material condition were analyzed to improve statistics and mitigate the influence of local heterogeneities. The cluster analysis variables were estimated using an iterative method, as demonstrated by Swenson and Wharry [ 62 ]. The \(\:{d}_{max}\) and \(\:{N}_{min}\) values used for materials exhibiting clustering were 1.4 nm and 18 ions, respectively. The maximum separation method was used to estimate the size, volume fraction, and number density of nanoprecipitates. Declarations Data availability The data supporting the findings of this study are available from the corresponding author upon request. Acknowledgements The authors thank Dr. Donna Guillen, Jeremy Burgener, Jana Howard, and Alina Montrose of Idaho National Laboratory for their assistance with irradiation experiments and specimen handling and coordination. Funding Irradiation experiments and post-irradiation examination were supported by the U.S. Department of Energy, Office of Nuclear Energy, through the Nuclear Science User Facilities (NSUF) award 15-8242. R.R. and J.W. acknowledge support from the U.S. Department of Energy, Office of Nuclear Energy, contract DE-NE0009513. This work was partially supported by the Electric Power Research Institute contract 10015819. Author Contributions Statement R.R. - Investigation, Formal Analysis, Data Curation, Writing - Original Draft, Writing - Review & Editing; S.M. - Investigation, Formal Analysis, Writing - Review & Editing; C.C. - Investigation, Formal Analysis, Data Curation, Writing - Review & Editing; N.P. - Investigation, Formal Analysis; Y.L. - Investigation, Formal Analysis, Writing - Review & Editing; Y.W. - Investigation, Formal Analysis, Writing - Review & Editing; B.S. - Conceptualization, Resources, Funding Acquisition; D.G. - Conceptualization, Resources, Funding Acquisition; J.W. - Conceptualization, Supervision, Funding Acquisition, Writing - Review & Editing. Competing interest The authors declare that they have no competing interests that could be perceived to influence the results and/or discussion reported in this paper. References G.S. 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Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 23 Feb, 2026 Reviews received at journal 21 Feb, 2026 Reviews received at journal 18 Feb, 2026 Reviewers agreed at journal 09 Feb, 2026 Reviewers agreed at journal 22 Jan, 2026 Reviewers agreed at journal 19 Dec, 2025 Reviews received at journal 13 Dec, 2025 Reviewers agreed at journal 03 Dec, 2025 Reviewers invited by journal 25 Nov, 2025 Editor assigned by journal 24 Nov, 2025 Submission checks completed at journal 23 Nov, 2025 First submitted to journal 19 Nov, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8157703","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":550995550,"identity":"fdce867d-a4f8-45bb-86d2-ec631ecf6d49","order_by":0,"name":"Ronit 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14:47:06","extension":"html","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":218198,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/1864dc57b22a1c2d7e466b5c.html"},{"id":97171824,"identity":"f3ec037f-4ea0-40ab-b8aa-a3420c570a88","added_by":"auto","created_at":"2025-12-01 14:47:05","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":306674,"visible":true,"origin":"","legend":"\u003cp\u003eEngineering stress-strain response obtained from uniaxial tensile tests for non-irradiated and irradiated specimens with different irradiation damage and temperature for Alloy (a) 625 and (b) Alloy 690 fabricated via PM-HIP and Forged route.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/ceaa17d30bc588b937daa287.png"},{"id":97249000,"identity":"872c49e1-d2ba-473c-ae52-f5854c690bf3","added_by":"auto","created_at":"2025-12-02 13:09:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":539209,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of fracture surface observed after uniaxial tensile tests in PM-HIP Alloy 625 irradiated to (a) 1 dpa (as-run 0.53 dpa) and (b) 3 dpa (as-run 3.69 dpa). Fracture surfaces resulted from uniaxial tensile tests in forged Alloy 625 irradiated to (c) 1 dpa (as-run 0.52 dpa) and (d) 3 dpa (as-run 3.84 dpa).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/b6986698c4a63aaa4cf6ccfb.png"},{"id":97171825,"identity":"1c26884a-062d-4de3-9bc0-e0357906fe71","added_by":"auto","created_at":"2025-12-01 14:47:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":661498,"visible":true,"origin":"","legend":"\u003cp\u003eTEM bright field micrographs imaged using through-focus technique representing voids in (a-b) PM-HIP Alloy 625, (c-d) PM-HIP Alloy 690, (e-f) Forged Alloy 625 and (g-h) Forged Alloy 690 irradiated up to 1 and 3 dpa. Voids are highlighted with yellow arrows.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/824b8e5553be310d467b58f4.png"},{"id":97249110,"identity":"6614f4f0-9e6e-4f0f-8da9-81ec1591b4a4","added_by":"auto","created_at":"2025-12-02 13:10:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":211092,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the average size and number density (in log scale) of voids resulting from 1 dpa and 3 dpa irradiation in Alloy 625 and Alloy 690, fabricated via PM-HIP and forged routes.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/b1b73076a1b1a967831bac0b.png"},{"id":97249118,"identity":"f298dc31-983a-4a66-9eef-4ce42dc4d177","added_by":"auto","created_at":"2025-12-02 13:10:32","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":574195,"visible":true,"origin":"","legend":"\u003cp\u003eTEM bright field micrographs taken at g vector \u0026nbsp;\u0026nbsp;(011) \u0026nbsp;\u0026nbsp;imaging reflection representing irradiation-induced microstructure in (a-b) PM-HIP Alloy 625, (c-d) PM-HIP Alloy 690, (e-f) Forged Alloy 625 and (g-h) Forged Alloy 690 irradiated up to 1 and 3 dpa. SFTs are highlighted with yellow circles, loops are highlighted with yellow arrows and edge-on loops are highlighted with red arrows.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/633e7f6d319147b4bbffedfa.png"},{"id":97249126,"identity":"7e77a48c-51fa-49a6-ad32-efebe2572e7f","added_by":"auto","created_at":"2025-12-02 13:10:36","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":213942,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the average size and number density (in log scale) of loops resulting from 1 dpa and 3 dpa irradiation in Alloy 625 and Alloy 690, fabricated via PM-HIP and forged routes.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/8c83f097c6009d3cdd4902e4.png"},{"id":97250401,"identity":"dd36d58d-d5ea-4428-a99e-2ed4169e0c02","added_by":"auto","created_at":"2025-12-02 13:14:26","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":821560,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative APT tip 3D reconstructions of Ni and Si, representing Si clusters in (a-b) PM-HIP Alloy 625, (c-d) Forged Alloy 625, (e-f) PM-HIP Alloy 625, and (g-h) Forged Alloy 690 irradiated up to 1 and 3 dpa.\u003cstrong\u003e \u003c/strong\u003eProminent Si Clusters are only observed in the PM-HIP Alloy 625. Small amalgamations of Si atoms are shown in the enlarged images taken from 3 dpa specimens among PM-HIP Alloy 690 and Forged Alloy 625 \u0026amp; 690.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/ebf5aa2960f7ffe834499089.png"},{"id":97250603,"identity":"ac2670f5-59f9-477f-bab5-c8768003e52a","added_by":"auto","created_at":"2025-12-02 13:14:47","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":327059,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the size distribution of (a) loops and (b) voids with a 95% confidence interval, resulting from 1 dpa and 3 dpa irradiation in Alloy 625 and Alloy 690, fabricated via PM-HIP and forged routes. The corresponding FWHM values for different size distributions are provided in Table 4.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/a63e360a6bdad345567d4fd1.png"},{"id":97171847,"identity":"14145eaf-c238-4aed-9e56-b7313d050087","added_by":"auto","created_at":"2025-12-01 14:47:06","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":284860,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of irradiation hardening from uniaxial tensile tests and DBH model estimations for Alloy 625 and Alloy 690 fabricated via PM-HIP and forged routes. The experimental data used for the comparison are highlighted in bold in Table 1.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/519d0283ae4c463740c2fffb.png"},{"id":97367875,"identity":"553a09e3-72bb-44b8-8b2e-b6bbd3a323a1","added_by":"auto","created_at":"2025-12-03 16:20:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4993649,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8157703/v1/9df87960-2dd1-46aa-95bd-152cd3bd0243.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of Neutron Irradiation on Ni-Based Alloys: A Comparative Study Between PM-HIP and Forging","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe structural components of nuclear reactors are exposed to extreme conditions, such as irradiation, high temperature, and highly corrosive environments during their service life [\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Hence, the integrity and stability of structural components are key to ensuring safe and economical operation of nuclear reactors. Traditionally, these components have been manufactured by forging or casting methods [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, these manufacturing methods often result in casting or forging defects, such as pinholes, blowholes, cold shuts and hot cracking [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, near-net (component) shape productions are extremely challenging with the aforementioned techniques; thus, extensive post-processing techniques, such as machining and welding, are often required [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. This can generate weak points in the components and make inspection and quality control challenging, especially during operations. Recent advancements in manufacturing methods have overcome these problems, alongside providing enhanced microstructure and mechanical properties with a more economical production. Thus, these new manufacturing methods are being considered for future nuclear reactor structural components [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePowder metallurgy with hot isostatic pressing (PM-HIP) is a powder-based advanced manufacturing technique that takes advantage of solid-state diffusion. During PM-HIP, gas atomized metallic powders are consolidated under 100 MPa to 150 MPa isostatic pressure at temperatures typically above 70% of the melting temperature (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\ge\\:0.7{T}_{m}\\)\u003c/span\u003e\u003c/span\u003e) of the material [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Compared with traditional casting or forging, PM-HIP components are fabricated in a near-net shape, minimizing the post-processing steps and reducing the cost. Moreover, PM-HIP components offer greater density, chemical homogeneity, equiaxed grain structure, fewer defects and enhanced mechanical properties, compared to their cast or forged counterparts [\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In recent years, PM-HIP components of ferritic, austenitic stainless steels, and Ni-alloys have been certified for non-nuclear applications [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Most recently, the PM-HIP fabrication technique has also been qualified to manufacture 316L stainless steel components for secondary circuits of nuclear reactors [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Nowadays, the nuclear industry has shown utmost interest in certification of PM-HIP components for use on the primary circuit [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, such certification requires an understanding of the performance of PM-HIP components under irradiation [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], which is the primary objective of the present study.\u003c/p\u003e\u003cp\u003eDespite the broad applications for PM-HIP manufacturing in nuclear energy systems, work on understanding the irradiation response of PM-HIP materials is limited [\u003cspan additionalcitationids=\"CR20 CR21 CR22\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Clement et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] presented a systematic comparison of irradiation response between PM-HIP and traditionally manufactured Alloy 625 under both ion and neutron irradiation. It was reported that the PM-HIP alloy exhibits superior mechanical behaviour, such as ductility and tensile strength, compared to its forged counterparts. A similar comparison between PM-HIP and forged low-carbon steel SA508 was reported by Jiang et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. After irradiation, PM-HIP SA508 has a similar estimated toughness but shows superior ductility at maximum load-bearing capacity than the forging. Work by Wharry et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] also reported lower irradiation hardening and greater ductility in PM-HIP manufactured 316L stainless steel than its cast counterpart. Subsequently, Chatterjee et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] explained that this superior PM-HIP ductility was associated with pseudoelasticity that occurs uniquely in irradiated PM-HIP 316L. Recent work on PM-HIP Grade 91 steel also reported superior mechanical performance over its cast counterpart [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOverall, these aforementioned superior mechanical behaviors of PM-HIP compared to cast or forged materials, which include ferritic and austenitic steels as well as Ni-based alloys, can generally be associated with greater resistance to the formation of irradiation-induced extended defects such as loops, cavities, and nanoprecipitates [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. These studies show that PM-HIP components exhibit more promising performance compared to traditionally manufactured components under irradiation, which facilitates the potential use of these components in the nuclear industry. However, these studies have probed only low irradiation doses\u0026thinsp;~\u0026thinsp;1 displacement per atom (dpa), leaving opportunity and need for further studies at higher doses to understand the irradiation response of PM-HIP components over their expected service life.\u003c/p\u003e\u003cp\u003eIn the current study, we selected two Ni-based alloys, i.e., Alloys 625 and 690, since this alloy class is a leading candidate for internal and structural components in future generation reactors. In the current fleet of light-water reactors, Ni-based alloys are mostly used in heat exchangers and steam generators on the secondary circuit, owing to their high temperature performance and superior corrosion resistance [\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. But as these components are not exposed to direct and significant irradiation, studies on the irradiation response of Ni-based alloys are limited. However, in recent years, these alloys have been considered as potential structural material for advanced Gen IV reactors, such as molten salt reactors (MSR), small modular reactors (SMR) and gas-cooled very high temperature reactors (VHTR) [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In such reactor operating environments, these components are expected to operate at temperatures as high as 700\u0026deg;C and accumulate doses up to 100 dpa over their service life [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Moreover, these Ni-based alloys are susceptible to precipitate hardening and embrittlement (related to the formation of embrittling phases) over time under non-irradiated environments [\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The rate of formation of such precipitate and embrittling phases is further enhanced under exposure to irradiation [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Hence, understanding the irradiation response of these Ni-based alloys coupled with the PM-HIP manufacturing process is particularly important for identifying and qualifying an advanced, economical, and modular heavy component manufacturing supply chain for Gen IV reactors.\u003c/p\u003e\u003cp\u003eIn the present study, we characterize the irradiation response of Alloys 625 and 690 under neutron irradiation and provide a one-to-one comparison between the PM-HIP and forged manufacturing routes at two different damage levels. For this purpose, transmission electron microscopy (TEM) discs and threaded tensile bars are neutron irradiated up to 1 dpa and 3 dpa damage levels at ~\u0026thinsp;400\u0026deg;C target temperature. The mechanical properties of the tensile specimens are evaluated following American Society for Mechanical Engineers (ASME) E8 tensile tests, and the irradiation-induced microstructures are characterized using a combination of scanning transmission electron microscopy (S/TEM) and atom probe tomography (APT). Further, the correlation between the irradiated microstructure and the estimated mechanical properties is established in terms of initial sink strength. The current observations contribute to a wider understanding of the irradiation response of Ni-based alloys in combination with PM-HIP manufacturing.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eTensile Tests\u003c/h2\u003e\n \u003cp\u003eThe engineering stress-strain curves obtained from the uniaxial tensile tests for PM-HIP and forged specimens for Alloys 625 and 690 are presented in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The yield strength of each specimen is calculated with a 0.2% strain offset. The details of tensile specimen irradiation conditions, yield strength (YS), ultimate tensile strength (UTS), uniform elongation (UE), total elongation (TE), and irradiation hardening are summarized in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. We note that the non-irradiated and 1 dpa irradiated data for Alloy 625 presented here have been previously reported in ref. [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, to maintain continuity and for completeness, we include those observations here.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003e\u0026nbsp;Details of irradiation and corresponding mechanical properties obtained from uniaxial tensile tests\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAlloy\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFabrication\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAs-Run Dose (dpa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAs-Run Average Temperature (\u0026ordm;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLoad at Yield (kN)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMax. Load (kN)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eYS (Pa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eUTS (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eUE (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTE (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eIrradiation Hardening (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"9\"\u003e\n \u003cp\u003e625\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"5\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e462.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e768.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e52.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e321\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e529\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1003.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e66.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e339\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e546.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1010.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e84.7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e367\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e830.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1104.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e367.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e384\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e664.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1034.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e202.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"4\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e455.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e861.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e338\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e601.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e964.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e146.1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e355\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34,4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e694.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1087.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e238.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e380\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e714.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e948.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e258.5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"10\"\u003e\n \u003cp\u003e690\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"5\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e91.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e290.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e675.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e54.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e368\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e501.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e790.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e211.3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e342\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e510.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e788.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e42.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e220.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e378\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e714.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e884.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e424.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e378\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e728.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e897.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e437.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"5\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e248.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e636.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e335\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e472.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e790.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e224.6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e358\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e521.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e791.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e48.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e273.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e373\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e626.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e809.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e378.7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e385\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e736.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e825.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e488.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe non-irradiated PM-HIP and forged Alloy 625 exhibit identical YS. However, a decrease in UTS is observed in the PM-HIP Alloy 625 compared to the forged counterpart. For Alloy 625, similar observations have been reported by Guillen et al. [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. The elongation (UE and TE) for both PM-HIP and forged Alloy 625 is nearly similar, with a slightly lower elongation observed in the PM-HIP material. Similar values have been previously reported [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. Unlike Alloy 625, a small increase in both YS and UTS is observed in non-irradiated PM-HIP Alloy 690 compared to its forged counterpart. However, elongation comparison between PM-HIP and forged Alloys 690 is nearly identical to what was observed for Alloy 625, i.e., the forged Alloy 690 exhibits a slightly higher elongation than PM-HIP.\u003c/p\u003e\n \u003cp\u003eFor Alloy 625, the increase of YS due to irradiation in PM-HIP material is considerably smaller than that observed in the forged material at ~\u0026thinsp;0.5 dpa damage, resulting in lower irradiation hardening. Identical behaviour is also seen in the PM-HIP and forged Alloy 625 materials, irradiated at ~\u0026thinsp;0.7 dpa and ~\u0026thinsp;3.85 dpa. However, we note that one of the PM-HIP datasets, irradiated at 3.69 dpa, exhibits contradictory behaviour, with a very high increase of YS. Since no such behaviour has been previously reported for PM-HIP Alloy 625, this specimen may be an outlier of the experimental set. In addition, we acknowledge that having only a single tensile specimen at a given neutron irradiation condition inherently limits statistical confidence and repeatability, but this is an inherent limitation of the availability of irradiated material for testing. Regarding ductility, both PM-HIP Alloy 625 specimens irradiated at 0.53 dpa and 0.73 dpa exhibit a higher TE than the forged specimens. On the other hand, the PM-HIP Alloy 625 specimen irradiated at 3.69 dpa exhibits slightly lower TE than the forged specimen irradiated at 3.84 dpa. Since the PM-HIP Alloy 625 specimen irradiated at 3.93 dpa fractured prematurely, it is not considered in the reduction of ductility estimates. Overall, these results suggest that PM-HIP Alloy 625 exhibits similar or greater resistance to irradiation-induced hardening and ductility reduction compared to the forged counterpart.\u003c/p\u003e\n \u003cp\u003eFor Alloy 690, the PM-HIP specimens irradiated at 0.86 dpa and 0.99 dpa exhibit a nearly identical or an increase in YS compared to the forged specimens. Similar characteristics are also observed among the PM-HIP and forged Alloy 690 specimens at higher damage levels. Regarding ductility, PM-HIP Alloy 690 specimens show a lower TE at 0.86 dpa and 0.99 dpa than their forged counterparts. But the difference between PM-HIP and forged Alloy 690 diminishes as the damage level increases, as the initial loss of ductility in PM-HIP alloys levels off with saturation of defect structures at higher damage levels. These observations suggest the PM-HIP and forged Alloy 690 exhibit nearly identical mechanical responses under irradiation.\u003c/p\u003e\n \u003cp\u003eTo further investigate the tensile behaviour, the fracture surface images are collected, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Due to radioactive specimen handling limitations, fractography is conducted only on Alloy 625, as we found greater differences in the tensile behaviour between PM-HIP and forged Alloy 625 compared to Alloy 690. At ~\u0026thinsp;1 dpa, both PM-HIP and forged Alloy 625 specimens show evidence of cup and cone fracture with a significant number of dimples, resembling a ductile fracture mode. With increasing damage level, the fracture surfaces resemble a more brittle fracture mode with significantly fewer dimples for both PM-HIP and forged Alloy 625. However, no notable differences in fracture surface morphology between PM-HIP and forged Alloy 625 are apparent at either damage level.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eIrradiation-Induced Microstructure\u003c/h3\u003e\n\u003cp\u003eUpon exposure to neutron irradiation, face-centred cubic (FCC) materials undergo microstructural changes, such as formation of dislocation loops, voids, and stacking fault tetrahedra (SFT). Moreover, the size and density of these features are also influenced by the fluence and flux of the irradiation. The forthcoming results will present these microstructural changes depending on alloys, irradiation doses and temperatures.\u003c/p\u003e\n\u003cp\u003eThe distribution of irradiation-induced voids in both PM-HIP and forged alloys is shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. For both Alloys 625 and 690, a relatively homogenous spatial distribution of voids can be observed in each specimen. However, the average size and number density of the voids differ based on the Alloy and respective damage level. The details of the average void size and number density are quantified and provided in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and are plotted in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. The average void size observed in the PM-HIP and forged Alloy 625 is statistically identical at each damage level, ~\u0026thinsp;2 nm. Although the average void size tends to decrease slightly with increasing damage levels (and also irradiation temperature) in both PM-HIP and forged Alloy 625, the changes fall within the standard error. These trends differ from typical reports in which the void size tends to increase with damage level either without bound [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e] or until saturation [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]. Apart from that, PM-HIP Alloy 625 exhibits significantly lower void number density than its forged counterpart at both damage levels, i.e., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim0.9\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e in PM-HIP compared to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim3.6\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e in forged Alloy 625. In addition, the void number density in both PM-HIP and forged Alloy 625 increases by about an order of magnitude from 1 to 3 dpa.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSummary of irradiation-induced microstructure evolution with DBH model estimated irradiation hardening for each type of defect.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAlloy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eFabrica-tion\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAs-Run Dose (dpa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAs-Run Average Temperature (\u0026ordm;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eDislocation loops\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eVoids\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eSFTs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eClusters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eTotal \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{\u0026sigma;}}_{\\text{sy}}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003e(MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eMeasured \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{\u0026sigma;}}_{\\text{sy}}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003e(MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{N}\\:({10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ed (nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{\u0026sigma;}}_{\\text{sy}}\\:\\)\u003c/span\u003e\u003c/span\u003e(MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{N}\\:({10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ed (nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{\u0026sigma;}}_{\\text{sy}}\\:\\)\u003c/span\u003e\u003c/span\u003e(MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{N}\\:({10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ed (nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{\u0026sigma;}}_{\\text{sy}}\\:\\)\u003c/span\u003e\u003c/span\u003e(MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{N}\\:({10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ed (nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{\u0026sigma;}}_{\\text{sy}}\\:\\)\u003c/span\u003e\u003c/span\u003e(MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"4\"\u003e\n \u003cp\u003e625\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e385\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e75.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45.16\u0026thinsp;\u0026plusmn;\u0026thinsp;8.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e39.0\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.13\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e151.9\u0026thinsp;\u0026plusmn;\u0026thinsp;14.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e385\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.11\u0026thinsp;\u0026plusmn;\u0026thinsp;3.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.59\u0026thinsp;\u0026plusmn;\u0026thinsp;1.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e86.89\u0026thinsp;\u0026plusmn;\u0026thinsp;7.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e174.0\u0026thinsp;\u0026plusmn;\u0026thinsp;8.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e146.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e398\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.13\u0026thinsp;\u0026plusmn;\u0026thinsp;5.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e136.62\u0026thinsp;\u0026plusmn;\u0026thinsp;3.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.22\u0026thinsp;\u0026plusmn;\u0026thinsp;4.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.71\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e115.43\u0026thinsp;\u0026plusmn;\u0026thinsp;18.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.74\u0026thinsp;\u0026plusmn;\u0026thinsp;1.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e308.1\u0026thinsp;\u0026plusmn;\u0026thinsp;28.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e202.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e398\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.78\u0026thinsp;\u0026plusmn;\u0026thinsp;7.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e117.63\u0026thinsp;\u0026plusmn;\u0026thinsp;1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.86\u0026thinsp;\u0026plusmn;\u0026thinsp;3.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e232.53\u0026thinsp;\u0026plusmn;\u0026thinsp;5.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e381.7\u0026thinsp;\u0026plusmn;\u0026thinsp;8.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e258.52\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"4\"\u003e\n \u003cp\u003e690\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e388\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.42\u0026thinsp;\u0026plusmn;\u0026thinsp;5.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.75\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.72\u0026thinsp;\u0026plusmn;\u0026thinsp;1.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.57\u0026thinsp;\u0026plusmn;\u0026thinsp;5.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e159.3\u0026thinsp;\u0026plusmn;\u0026thinsp;7.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e211.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e389\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.66\u0026thinsp;\u0026plusmn;\u0026thinsp;4.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e68.71\u0026thinsp;\u0026plusmn;\u0026thinsp;1.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.46\u0026thinsp;\u0026plusmn;\u0026thinsp;2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e89.98\u0026thinsp;\u0026plusmn;\u0026thinsp;2.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e158.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e224.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e398\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.43\u0026thinsp;\u0026plusmn;\u0026thinsp;7.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e99.14\u0026thinsp;\u0026plusmn;\u0026thinsp;2.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.58\u0026thinsp;\u0026plusmn;\u0026thinsp;1.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e116.23\u0026thinsp;\u0026plusmn;\u0026thinsp;7.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e232.8\u0026thinsp;\u0026plusmn;\u0026thinsp;10.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e424.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e398\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.18\u0026thinsp;\u0026plusmn;\u0026thinsp;8.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e97.57\u0026thinsp;\u0026plusmn;\u0026thinsp;1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.31\u0026thinsp;\u0026plusmn;\u0026thinsp;1.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e150.54\u0026thinsp;\u0026plusmn;\u0026thinsp;6.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e267.4\u0026thinsp;\u0026plusmn;\u0026thinsp;8.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e378.71\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eIn Alloy 690, the average void sizes in the PM-HIP and forged materials are statistically identical at each damage level. Additionally, the average void size tends to decrease with increasing damage level for both PM-HIP and forged Alloy 690, i.e., ~\u0026thinsp;4 nm at 1 dpa to ~\u0026thinsp;2 nm at 3 dpa. PM-HIP Alloy 690 has a lower void number density than the forged material at all damage levels (e.g., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim1.7\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e in PM-HIP and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim2.0\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e in forged at 1 dpa), although this difference between PM-HIP and forged void number densities is not as pronounced as that observed in Alloy 625. The void number densities in both PM-HIP and forged Alloy 690 increase with damage level, but this increase is not as significant as that observed in Alloy 625.\u003c/p\u003e\n\u003cp\u003eThe distribution of irradiation-induced dislocation loops and SFTs in both Alloys 625 and 690 is presented in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. The details of average size and number density for both dislocation loops and SFTs are quantified and provided in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, with a comparison of average dislocation loop size and density plotted in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. At both damage levels, the average size of dislocation loops in the PM-HIP Alloy 625 is smaller than that observed in the forged material, (e.g., ~\u0026thinsp;5 nm in PM-HIP and ~\u0026thinsp;8 nm in forged Alloy), though within error bars. An increase in average dislocation loop size in both PM-HIP and forged Alloy 625 is observed with increasing damage levels (e.g., from ~\u0026thinsp;5 nm at 1 dpa to ~\u0026thinsp;11 dpa at 3 dpa in PM-HIP Alloy), which is identical to previous reports based on Ni-based alloys [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. Unlike the average size, the number density of dislocation loops is greater in the PM-HIP Alloy 625 than in the forged material at both damage levels. The density tends to increase in PM-HIP Alloy 625 between 1 and 3 dpa (i.e., from \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim14\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e at 1 dpa to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim20\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e at 3 dpa). Similar observations have been previously reported in Ni-based alloys [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, the dislocation loop number density decreases slightly in forged Alloy 625 between 1 and 3 dpa (i.e., from \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim11\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e at 1 dpa to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim9\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e at 3 dpa). This likely results from loop coarsening, but may also be attributed to local heterogeneities and the small region of interest (ROI) sampled in a single TEM lamella.\u003c/p\u003e\n\u003cp\u003eThe average dislocation loop size among both PM-HIP and forged Alloy 690 is nearly identical (~\u0026thinsp;14 nm) and does not follow specific trends like Alloy 625. No apparent increase in average dislocation loop size in both PM-HIP and forged Alloys 690 is observed with increasing damage level. In Alloy 690, a slightly higher number density of dislocation loops is observed in the PM-HIP compared to the forged material at both damage levels (e.g., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim6.2\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e in PM-HIP \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim5.0\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e in forged at 1 dpa), although the difference is within standard error at the highest damage level. In addition, a slight increase in dislocation loop number density is observed in both PM-HIP and forged Alloy 690 with increasing damage levels (e.g., from \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim5.0\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e at 1 dpa to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim7.3\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e at 3 dpa in the forged Alloy).\u003c/p\u003e\n\u003cp\u003eSFTs are only found at the highest damage levels in Alloys 625 and 690. The average size of SFTs in both PM-HIP Alloys 625 and 690 tends to be slightly smaller than in the respective forged Alloys (e.g., ~\u0026thinsp;9 nm and ~\u0026thinsp;12 nm in PM-HIP and forged Alloy 625, respectively). In Alloy 625, the SFT number density is four times smaller in the PM-HIP than in the forged material. But in Alloy 690, the SFT number densities in both PM-HIP and forged Alloy 690 are identical, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim0.5\\times\\:{10}^{21}\\:{m}^{-3}\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e\n\u003ch3\u003eNanoprecipitates\u003c/h3\u003e\n\u003cp\u003eRepresentative 3D reconstructions of the APT needles for both PM-HIP and forged Alloy 625 are presented in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. The chemical composition of APT needles is provided in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Si nanoclustering, quantified in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, is only observed in the PM-HIP Alloy 625 at both damage levels. This is likely associated with the higher bulk Si concentration in the PM-HIP Alloy 625 than its forged counterpart. Another possibility is that the smaller dislocation loops in the PM-HIP Alloy 625 are weaker sinks, and thus limit the loss of Si to radiation-induced segregation (RIS) at dislocation loops and networks [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e], consequently leaving more Si in the matrix to form clusters. The average size of Si clusters remains statistically unchanged with increasing dose level, although their number density increases with damage.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eChemical composition of Alloy 625 and Alloy 690 estimated from APT analysis (in %atoms).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAlloy\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFabrication\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCr\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMo\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCo\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNb\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e625\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e64.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e690\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePM-HIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.009\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eForged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e32.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e55.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eThe absence of Si clusters in the forged Alloy 625 is surprising, since Clement et al. find Si clusters in forged Alloy 625 even at lower damage levels, i.e. ~0.5 dpa to 0.7 dpa [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. Evidence of Si clusters in traditionally manufactured Alloy 625 under both ion and proton irradiation is also reported by Yu and Marquis [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. However, in the latter work, Si clusters forming during 1.5 dpa Ni\u003csup\u003e+\u003c/sup\u003e ion irradiation are significantly smaller than those forming during 11 dpa proton irradiation. Despite the characteristic differences in the damage cascade morphologies and efficiencies generated by proton compared to heavy ion irradiation, these works from Yu and Marquis show that the damage level strongly influences the size of Si clusters [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. Damage levels in the present study are likely lower than may be required for the formation of prominent Si clusters in the forged Alloy 625 under neutron irradiation. Additionally, the stronger RIS at larger dislocation loops (i.e., stronger sinks) in the forged Alloy 625 delays the Si cluster formation in the matrix. However, small coalescences of Si atoms are observed in the forged Alloy 625 at ~\u0026thinsp;3 dpa damage level, as shown in the inset of Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(d). Note that all insets presented in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(d), (f) and (h) are taken from the edge, to minimize the visual effect of the needle thickness. These small Si atom coalescences are likely nucleation sites that will evolve into Si clusters at higher damage levels.\u003c/p\u003e\n\u003cp\u003eNo evidence of Si clusters is found in either PM-HIP or forged Alloy 690, despite having considerable bulk concentrations of Si, particularly in the PM-HIP Alloy 690. This can be attributed to the change in alloy composition between Alloy 625 and 690, specifically, the low fraction of secondary alloying elements in Alloy 690 may delay or prevent the formation of Si clusters. We note that Yu reported that Si clusters are found in conventionally manufactured Alloy 690 under proton irradiation, although the distribution is not homogeneous at all irradiation doses and temperatures [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e]. In the current study, the dislocation loops formed in Alloy 690 (both PM-HIP and forged) are comparable to the forged Alloy 625 dislocation loop size, which possibly delays the formation of Si clusters by RIS at dislocation loops. Nonetheless, small coalescences of Si atoms are observed in both PM-HIP and forged Alloy 690 at ~\u0026thinsp;3 dpa damage level, similar to forged Alloy 625.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eDislocation Loop and Void Distribution\u003c/h2\u003e\u003cp\u003eTo further explain the evolution of dislocation loop and void sizes among all specimens, the frequency distributions of the void and dislocation loop sizes with 95% confidence intervals for both fabrication methods of Alloys 625 and 690 are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The corresponding full width at half maximum (FWHM) values are estimated and provided in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. A higher FWHM value represents a broader size distribution, i.e., less uniform size distribution.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFWHM values of loop and void size distributions (in no. of bins).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDose (dpa)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e\u003cp\u003e1 dpa\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e\u003cp\u003e3 dpa\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlloy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e625\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e690\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e625\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e690\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFabrication\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePM-HIP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eForged\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePM-HIP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eForged\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003ePM-HIP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eForged\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePM-HIP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eForged\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLoops\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVoids\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn Alloy 625, the dislocation loop size distribution tends to broaden and shift rightward with increasing damage level in both the forged and PM-HIP materials. However, the forged material exhibits a broader size distribution than the PM-HIP material, especially at higher damage levels. This, together with the decrease in the dislocation loop number density in forged Alloy 625 at higher damage levels, suggests that the loop population has reached saturation by \u0026le;\u0026thinsp;3 dpa. Meanwhile, in PM-HIP Alloy 625, loops continue to nucleate and grow between the damage levels studied, suggesting saturation has not yet occurred by 3 dpa. On the other hand, the dislocation loops formed in Alloy 690 exhibit a broad, non-uniform size distribution, with little difference between the PM-HIP and forged material. Although the dislocation loop size distributions broaden slightly with increasing damage level, the loop microstructure in Alloy 690 appears generally saturated by ~\u0026thinsp;1 dpa.\u003c/p\u003e\u003cp\u003ePM-HIP and forged Alloy 625 exhibit a uniform void size distribution at lower damage levels, which tends to broaden and also skew to smaller sizes at higher damage levels. This indicates that more voids are nucleating with increasing damage level, while the existing voids grow in size. This explains the relatively unchanged average void size and significant increase in void number density in both PM-HIP and forged Alloy 625 between 1 and 3 dpa. By contrast, the void size distributions in both PM-HIP and forged Alloy 690 are significantly broader, suggesting that non-uniformly sized voids are already present at lower damage levels. These void size distributions tend to skew leftward with increasing damage level, again demonstrating that more void nucleation is occurring than void growth in Alloy 690 between 1 and 3 dpa, similar to Alloy 625.\u003c/p\u003e\u003cp\u003eIn both Alloys 625 and 690, a greater number density of voids is observed in forged than in PM-HIP alloys. This can be correlated to the initial dislocation density in forged alloys [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. As dislocations act as preferred sinks for interstitials, a higher initial dislocation density significantly reduces the possibility of recombination between vacancies and interstitials. This leads to more supersaturation of vacancies and promotes the formation of more voids in the forged alloys. In tandem, PM-HIP Alloy 625 has finer grain sizes than the forged material [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. This will accelerate annihilation of both vacancies and interstitials at grain boundary sinks in the PM-HIP alloy, further reducing the population of vacancies in PM-HIP Alloy 625. Hence, the void number densities in PM-HIP Alloy 625 are generally the lowest amongst all materials and conditions studied.\u003c/p\u003e\u003cp\u003eFinally, the difference in irradiation-induced defect population between Alloys 625 and 690 is attributed to the concentration of secondary elements in each alloy. Alloy 625 has a greater total concentration of secondary elements, including more Mo, but less Cr, than Alloy 690. These secondary alloying species exhibit different defect\u0026ndash;solute interactions that can explain the dislocation loop and void microstructures. Li et al. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] conducted He ion irradiation on pure Ni and binary Ni\u003csub\u003e0.9\u003c/sub\u003eCr\u003csub\u003e0.1\u003c/sub\u003e and Ni\u003csub\u003e0.9\u003c/sub\u003eMo\u003csub\u003e0.1\u003c/sub\u003e. They report that Mo has the most pronounced effect on increasing the number density of He bubbles (although those bubbles are smaller) due to its role in enhancing lattice stability and increasing migration barriers. This mechanism can explain the greater void number density in Mo-containing Alloy 625 than in Alloy 690. Li and coworkers [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] also find that Cr acts as a favorable trapping site to stabilize dislocation loops at sizes where the loops would have otherwise unfaulted. This can explain the larger loop sizes in Alloy 690, which has higher Cr content than Alloy 625. Similar defect\u0026ndash;solute trapping effects, which lead to greater accumulation of irradiation-induced extended defects (e.g., loops and voids), are routinely observed at strongly undersized or strongly oversized substitutional solutes in steels [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], including B, Mn, and P in ferritic steels [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] or Cr in austenitic steel [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eIrradiation Hardening\u003c/h2\u003e\u003cp\u003eUnder exposure to irradiation, the yield strength tends to increase, known as irradiation hardening \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left(\\varDelta\\:{\\sigma\\:}_{y}\\right)\\)\u003c/span\u003e\u003c/span\u003e. This results from the interaction between irradiation-induced defects and the movement of dislocations [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. The Orowan dispersed barrier hardening (DBH) model is typically used to estimate \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:{\\sigma\\:}_{y}\\)\u003c/span\u003e\u003c/span\u003e in a material by calculating the hardening contribution from each irradiation-induced defect types or sinks [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The DBH model can be expressed as,\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\varDelta\\:{\\sigma\\:}_{yi}={\\alpha\\:}_{i}M\\mu\\:b\\sqrt{{N}_{i}{d}_{i}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eWhere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\alpha\\:}_{i}\\)\u003c/span\u003e\u003c/span\u003e is the strength factor of the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{i}^{th}\\)\u003c/span\u003e\u003c/span\u003e type sink or irradiation-induced defect [\u003cspan additionalcitationids=\"CR51\" citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:M\\)\u003c/span\u003e\u003c/span\u003e is the Taylor factor [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:b\\)\u003c/span\u003e\u003c/span\u003e are the shear modulus and Burgers vector, respectively [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]; and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{N}_{i}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{d}_{i}\\)\u003c/span\u003e\u003c/span\u003e are the number density and average size of the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{i}^{th}\\)\u003c/span\u003e\u003c/span\u003e type sink or irradiation-induced defect.\u003c/p\u003e\u003cp\u003eIn the present study, a total of four types of irradiation-induced defects are considered: dislocation loops, voids, SFTs and Si clusters. The details of the DBH model parameters used for the present study are listed in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. We note that the strength factors are selected for both Alloys 625 and 690, which provides a reasonable degree of correlation with the experimental observations. Among all sinks, voids exhibit the most significant \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\alpha\\:\\)\u003c/span\u003e\u003c/span\u003e. Si clusters are associated with the smallest \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\alpha\\:\\)\u003c/span\u003e\u003c/span\u003e among all sinks, contributing the least to irradiation hardening. Similar assumptions have been previously used [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The DBH calculated hardening contributions for a given defect type are provided alongside their number densities and average sizes in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Notably, microstructural details used for the DBH model are estimated from the TEM specimens, whereas measured irradiation hardening is taken from tensile specimens. Although tensile and TEM specimens are irradiated to slightly different damage levels, this comparison provides a qualitative understanding of irradiation hardening and its correlation to different types of irradiation-induced defects.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDispersed barrier hardening model parameters.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAlloy\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e625\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e690\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eBurgers vector (\u003cem\u003eb\u003c/em\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.47 \u0026Aring;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.47 \u0026Aring;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eShear modulus (\u003cem\u003e\u0026micro;\u003c/em\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e81.4 GPa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e79.3 GPa\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eTaylor factor (\u003cem\u003eM\u003c/em\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.06\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eStrength Factor (\u003cem\u003eα\u003c/em\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLoop\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eVoid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSFT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCluster\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.03\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe irradiation hardening estimated from the tensile tests is compared with DBH model predictions and presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. For Alloy 625, the DBH model consistently overestimates the irradiation hardening compared to experimental measurements. This difference in hardening magnitude is associated with the higher damage level of the TEM specimens than the tensile specimens used in the current study. However, the DBH model accurately predicts that the PM-HIP material should exhibit less irradiation hardening than the forged counterpart at both damage levels, despite differences in the types of defects present. The DBH model also accurately predicts that both PM-HIP and forged Alloy 625 should exhibit an increase in irradiation hardening with increasing damage level. This is notable because of the significant increase in the hardening contribution from voids at the higher damage level. Previous reports have shown that voids result in significant irradiation hardening in irradiated Alloy 625 [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This is more evident in the forged Alloy 625, owing to the higher initial density of dislocations present in the material [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Dislocations act as a biased sink for interstitials, which leaves excess vacancies unable to recombine, thus promoting the nucleation of voids. Due to this, PM-HIP Alloy 625 tends to be more resistant to irradiation hardening than the forged material.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn Alloy 690, the DBH model actually underestimates irradiation hardening compared to experimental measurements, despite higher damage levels in the TEM specimens than in the tensile bars. This is likely associated with the Ni-Cr ratio, which is closer to 2.0 in both PM-HIP and forged Alloy 690 than in Alloy 625 [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. This Ni-Cr ratio favors the formation of Ni\u003csub\u003e2\u003c/sub\u003eCr (MoPt\u003csub\u003e2\u003c/sub\u003e-type) ordered nanoprecipitates under irradiation, which could explain the higher irradiation hardening in the experimental dataset [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Also, both measured and DBH estimated irradiation hardening is nearly identical between PM-HIP and forged Alloy 690 at respective damage levels. An increase in irradiation hardening is observed in both the measured and the DBH estimates in both PM-HIP and forged Alloy 690 with increasing damage level. The rise in void number density increases irradiation hardening between the damage levels in both PM-HIP and forged Alloy 690.\u003c/p\u003e\u003cp\u003eThe contributing factors behind the irradiation hardening observed in PM-HIP and forged Alloys 625 and 690 are demonstrated using the DBH model. A reasonable degree of correspondence between the DBH model and the experimentally measured irradiation hardening values has been observed. Overall, the PM-HIP Alloy 625 exhibits superior mechanical response to the forged Alloy 625 at all damage levels. However, no significant differences in the irradiation-induced changes in mechanical behaviour have been observed between PM-HIP and forged Alloy 690 at any damage level.\u003c/p\u003e\u003c/div\u003e"},{"header":"Summary","content":"\u003cp\u003eNuclear structural materials are subjected to various irradiation-induced damage, corrosion, and dimensional changes (swelling, irradiation creep, etc.), all of which can compromise mechanical integrity. As PM-HIP alloys are being considered as candidate materials for future generation reactor components, evaluating their performance under relevant reactor operating conditions is essential for certification and licensing for in-reactor use. The present study directly compares the response of PM-HIP and forged Ni-based Alloys 625 and 690 to neutron irradiation. For this purpose, both PM-HIP and forged materials are irradiated up to two different target damage levels, ~\u0026thinsp;1 dpa (actual doses 0.53\u0026ndash;1.09 dpa) and ~\u0026thinsp;3 dpa (actual doses 2.82\u0026ndash;4.27 dpa), at temperatures\u0026thinsp;~\u0026thinsp;330\u0026ndash;423 \u0026ordm;C. Further, the mechanical response and microstructural changes are compared to understand the irradiation-induced changes in the material behaviour. The following conclusions can be drawn:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eAt both damage levels, a lower population of irradiation-induced voids and smaller irradiation-induced dislocation loops are observed in the PM-HIP Alloy 625 compared to those observed in forged Alloy 625. These microstructural differences result in superior irradiated mechanical properties in the PM-HIP Alloy 625 than the forged counterpart.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe change in irradiation hardening between PM-HIP and forged Alloy 625 is associated with the density of initial dislocations, which act as biased sinks for interstitials. A higher initial dislocation density in forged Alloy 625 promotes supersaturation of vacancies and void formation, resulting in a more significant irradiation hardening than PM-HIP Alloy 625 at both damage levels.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eIn Alloy 690, irradiation-induced microstructures are almost identical between PM-HIP and forged materials at both damage levels. The only statistically significant difference is a lower void density in PM-HIP than in forged Alloy 690 at ~\u0026thinsp;3 dpa. Consequently, both PM-HIP and forged Alloy 690 exhibit nearly identical mechanical responses to both irradiation damage levels. This is associated with the lesser concentration of secondary elements in Alloy 690, which results in suppressed defect\u0026ndash;solute interactions and formation of fewer dislocation loops and voids compared to Alloy 625, which minimizes the difference in irradiation hardening between PM-HIP and forged Alloy 690.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSi nanoclusters are only observed in the PM-HIP Alloy 625. However, Si composition fluctuations, which are likely nucleation sites of Si clusters, are observed in forged Alloys 625 and 690, and in PM-HIP Alloy 690. The appearance of Si clustering in PM-HIP Alloy 625 is attributed to a combination of damage level, bulk Si concentration, and irradiation-induced dislocation loop size and density (RIS of Si at dislocation loops).\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe classical Orowan DBH model predictions of irradiation hardening capture the differences in mechanical behaviour between the PM-HIP and forged materials for both Alloys 625 and 690. However, Alloy 690 has a Ni-Cr ratio of ~\u0026thinsp;2, which promotes the formation of Ni\u003csub\u003e2\u003c/sub\u003eCr (MoPt\u003csub\u003e2\u003c/sub\u003e-type) ordered nanoprecipitates under irradiation; this explains why irradiation hardening in Alloy 690 exceeds the DBH predictions.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eThis work consistently demonstrates comparable or greater irradiation tolerance in PM-HIP Alloy 625 and 690 than in their forged counterparts. Results herein offer key data that can support qualification of PM-HIP manufacturing for Ni-based structural alloys to be deployed in future nuclear energy systems.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eMaterials, Specimen Preparation, and Irradiation\u003c/h2\u003e\u003cp\u003eSpecimens used in the current study were machined from Alloy 625 and 690 forged ingots and PM-HIP compacts supplied by the Electric Power Research Institute (EPRI). Alloys 625 and 690 PM-HIP compacts were fabricated by consolidating gas atomized alloy powders under 103 MPa pressure at 1149\u0026deg;C temperature for 4 hours. Further, the PM-HIP ingots were solution annealed at 1171\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u0026deg;C (for Alloy 625) or 1177\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u0026deg;C (for Alloy 690) for 2 hours, followed by water quenching [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. Both forged Alloy 625 and 690 ingots were cast and hot rolled, followed by solution annealing at 1040\u0026deg;C for 2 hours and then kept in ambient cooling for 40 minutes. Further, two heat treatments were carried out on both forged ingots. First, a solution annealing was carried out at 1075\u0026deg;C for 30 minutes, followed by water quenching, then the ingots were thermally aged at 700\u0026deg;C for 15 hours, followed by air cooling. The chemical compositions of the PM-HIP and forged ingots for Alloys 625 and 690 were analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and are provided in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eChemical composition of Alloy 625 and Alloy 690 (in %wt.).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"17\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlloy\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFabrication\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eP\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eCr\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eNi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eMo\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eTi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003eAl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c14\"\u003e\u003cp\u003eCo\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c15\"\u003e\u003cp\u003ePb\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c16\"\u003e\u003cp\u003eFe\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c17\"\u003e\u003cp\u003eNb\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e625\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePM-HIP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e21.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eBal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e8.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.006\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.010\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e\u003cp\u003e3.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eForged\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.006\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e23.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eBal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e7.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e\u003cp\u003e3.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e3.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e690\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePM-HIP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.019\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e30.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eBal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e\u003cp\u003e9.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eForged\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e31.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eBal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e\u003cp\u003e10.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e\u0026ndash;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTEM disc specimens and ASTM E8 standard threaded round tensile specimens were sectioned from PM-HIP compacts and forged ingots for Alloys 625 and 690 for characterization and mechanical testing. Electrical discharge machining (EDM) was used to cut the 3 mm diameter TEM discs from each material. Each disc was then mechanically polished using SiC paper up to 1200 grit to a final thickness of 250\u0026thinsp;\u0026plusmn;\u0026thinsp;10 \u0026micro;m, then electropolished in a 10% perchloric acid in methanol solution at -40\u0026deg;C and 35 V for 20 s prior to irradiation. The threaded round tensile specimens were machined using computer numerical control (CNC) machining to 76.2 mm length and 6.35 mm gauge diameter with a surface roughness of 3.2 \u0026micro;m. The detailed drawings for the tensile and disc specimens are provided in Guillen et al. [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOnce the tensile and disc specimens were prepared, the neutron irradiation was carried out at the Advanced Test Reactor (ATR) facility at Idaho National Laboratory (INL). Prior to insertion of specimens into the ATR, specimens were loaded into drop-in capsules to prevent contact with the reactor coolant. Each capsule was pressurized with a mixture of Ar and He to control the specimen temperature. As mentioned earlier, the target dose of specimens was set to 1 dpa and 3 dpa, and a target temperature of 400\u0026deg;C was selected. However, owing to the limited environmental control in a non-instrumented drop-in neutron irradiation capsule, the as-run doses experienced by the tensile specimens ranged between 0.53\u0026ndash;0.99 dpa and 2.82\u0026ndash;3.93 dpa for 1 dpa and 3 dpa target doses, respectively, and the as-run average temperature ranged between 330\u0026deg;C and 385\u0026deg;C. Similarly, the as-run doses experienced by the TEM discs ranged between 1.05\u0026ndash;1.09 dpa and 4.11\u0026ndash;4.27 dpa for 1 dpa and 3 dpa target doses, respectively, and the as-run average temperature ranged between 385\u0026deg;C and 398\u0026deg;C. Details of the capsule, assembly, irradiation experiment, as-run dose and temperature calculations are provided in ref. [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor microstructural and mechanical characterization in the present study, two irradiated disc specimens and two irradiated tensile bars for each material and were selected for testing and characterization [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Moreover, non-irradiated tensile and disc specimens from each material were also investigated as references. After irradiation, the capsules were disassembled at the Hot Fuel Examination Facility (HFEF) at INL. For microstructural characterization, the TEM discs were first decontaminated, then electropolished again with a 12.5% perchloric acid in ethanol solution at -17.5\u0026deg;C and 18 V. The tensile specimens were also decontaminated prior to testing.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eMechanical Testing\u003c/h2\u003e\u003cp\u003eAll uniaxial tensile tests (on both irradiated and non-irradiated specimens) were performed at the HFEF hot cell at INL using a 13M Instron load frame in accordance with the ASTM E8 standard. All uniaxial tensile tests were performed in an Ar environment at ambient temperature. For testing, an initial strain rate of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:8.78\\times\\:{10}^{-3}\\:{s}^{-1}\\)\u003c/span\u003e\u003c/span\u003e (corresponding displacement rate 0.279 mm/min) was used. After the specimens achieved 10% strain, the strain rate was increased to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:3.15\\times\\:{10}^{-2}\\:{s}^{-1}\\)\u003c/span\u003e\u003c/span\u003e (1.00 mm/min displacement rate), which was maintained until fracture. The details of uniaxial tensile testing are provided in ref. [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe resultant stress-strain curves from the uniaxial tensile tests were used to determine irradiation hardening \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left(\\varDelta\\:{\\sigma\\:}_{y}\\right)\\)\u003c/span\u003e\u003c/span\u003e, as the increase in yield strength resulted from irradiation, i.e., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:{\\sigma\\:}_{y}={\\sigma\\:}_{y,irr}-{\\sigma\\:}_{y,non-irr}\\)\u003c/span\u003e\u003c/span\u003e, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\sigma\\:}_{y,irr},\\:\\:{\\sigma\\:}_{y,non-irr}\\)\u003c/span\u003e\u003c/span\u003e are the yield strengths of the material before and after irradiation, respectively. After tensile tests, fractography on the tested specimens was carried out using a Tescan Lyra3 Scanning Electron Microscope (SEM) at HFEF.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eMicrostructural Characterization\u003c/h2\u003e\u003cp\u003eTo prepare TEM lamellae from the disc specimens, a focused ion beam (FIB)-enabled FEI Quanta 3D dual-beam SEM was used. A 2 \u0026times; 20 \u0026times; 3 \u0026micro;m Pt deposition was placed over a random region of interest for each TEM lamella. Next, trenches were milled on both sides of the Pt deposit, then the lamellae were cut free and lifted out. Then, the lamellae were transferred and mounted onto Cu TEM half-grids. Next, the lamellae were thinned using a gradually decreasing ion beam energy. At first, 30 kV Ga\u003csup\u003e+\u003c/sup\u003e ions at 1 nA current were used until a 150 \u0026micro;m thickness was achieved. Next, 5 kV Ga\u003csup\u003e+\u003c/sup\u003e ions at 0.26 nA current were used until the lamellae became electron transparent. Finally, the residual FIB damage and surface deposits were removed using 2 kV Ga\u003csup\u003e+\u003c/sup\u003e ions at 47 pA current.\u003c/p\u003e\u003cp\u003eThe same FIB-SEM was used to prepare the TEM lamellae and the APT specimens. To prepare APT specimens, lamellae were extracted from each specimen condition. They were cut into ~\u0026thinsp;1 \u0026micro;m slices and Pt-welded to a Si post. Needle-shaped specimens having a radius\u0026thinsp;\u0026lt;\u0026thinsp;100 nm were fabricated via an iterative top-down annular milling technique. A low-energy 5 kV polish and 2 kV final cleaning were successively used to eliminate damage associated with Ga penetration and/or FIB milling.\u003c/p\u003e\u003cp\u003eAn FEI Tecnai G2 F30 Scanning Transmission Electron Microscope (S/TEM) was used for the TEM analysis. Irradiation-induced dislocation loops were characterized following the down-zone bright field S/TEM technique [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. At first, the specimens were loaded into a double-tilt holder and tilted to the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\u0026lang;101\u0026rang;\\)\u003c/span\u003e\u003c/span\u003e zone axis. Further, the bright field S/TEM mode was enabled for dislocation loop imaging. The bright field S/TEM mode relaxes the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{g}\\bullet\\:\\stackrel{-}{b}\\)\u003c/span\u003e\u003c/span\u003e invisibility criterion and facilitates simultaneous imaging of all dislocation loops present in the material [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. The Fresnel contrast through-focus technique was used to image irradiation-induced voids in bright field TEM mode. In addition, the thickness of each TEM lamella was estimated using the zero-loss peak in electron energy loss spectroscopy (EELS). All TEM and S/TEM data were analyzed using TEM instrument analysis software and Gatan Digital Micrograph.\u003c/p\u003e\u003cp\u003eThe APT analysis was conducted on a Cameca Local Electrode Atom Probe 4000X HR instrument operating in laser pulse mode at 45 K base temperature. A pulse repetition rate of 200 kHz and a focused laser beam energy of 60 pJ were selected for all APT analyses. 3D data reconstruction of the APT needles was carried out using Cameca IVAS 3.8.6 software. At least two needles from each material condition were analyzed to improve statistics and mitigate the influence of local heterogeneities. The cluster analysis variables were estimated using an iterative method, as demonstrated by Swenson and Wharry [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. The \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{d}_{max}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{N}_{min}\\)\u003c/span\u003e\u003c/span\u003e values used for materials exhibiting clustering were 1.4 nm and 18 ions, respectively. The maximum separation method was used to estimate the size, volume fraction, and number density of nanoprecipitates.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data supporting the findings of this study are available from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank Dr. Donna Guillen, Jeremy Burgener, Jana Howard, and Alina Montrose of Idaho National Laboratory for their assistance with irradiation experiments and specimen handling and coordination.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIrradiation experiments and post-irradiation examination were supported by the U.S. Department of Energy, Office of Nuclear Energy, through the Nuclear Science User Facilities (NSUF) award 15-8242. \u0026nbsp; R.R. and J.W. acknowledge support from the U.S. Department of Energy, Office of Nuclear Energy, contract DE-NE0009513. \u0026nbsp;This work was partially supported by the Electric Power Research Institute contract 10015819.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eR.R. - Investigation, Formal Analysis, Data Curation, Writing - Original Draft, Writing - Review \u0026amp; Editing; S.M. - Investigation, Formal Analysis, \u0026nbsp;Writing - Review \u0026amp; Editing; C.C. - Investigation, Formal Analysis, Data Curation, Writing - Review \u0026amp; Editing; N.P. - Investigation, Formal Analysis; Y.L. - Investigation, Formal Analysis, Writing - Review \u0026amp; Editing; Y.W. - Investigation, Formal Analysis, Writing - Review \u0026amp; Editing; B.S. - Conceptualization, Resources, Funding Acquisition; D.G. - Conceptualization, Resources, Funding Acquisition; J.W. - Conceptualization, Supervision, Funding Acquisition, Writing - Review \u0026amp; Editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests that could be perceived to influence the results and/or discussion reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eG.S. 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Daymond, Evaluation of deformation fields associated with irradiation-induced growth and grain boundary interactions in zirconium, Materialia (Oxf) 39 (2025) 102325.\u003c/li\u003e\n\u003cli\u003eC. Clement, Y. Zhao, P. Warren, X. Liu, S. Xue, D.W. Gandy, J.P. Wharry, Comparison of ion irradiation effects in PM-HIP and forged alloy 625, Journal of Nuclear Materials 558 (2022) 153390.\u003c/li\u003e\n\u003cli\u003eC. Clement, S. Panuganti, P.H. Warren, Y. Zhao, Y. Lu, K. Wheeler, D. Frazer, D.P. Guillen, D.W. Gandy, J.P. Wharry, Comparing structure-property evolution for PM-HIP and forged alloy 625 irradiated with neutrons to 1 dpa, Materials Science and Engineering: A 857 (2022) 144058.\u003c/li\u003e\n\u003cli\u003eD.W. Gandy, J. Shingledecker, J. Siefert, Overcoming barriers for using PM/HIP technology to manufacture large power generation components, AM\u0026amp;P Technical Articles 170 (2012) 19\u0026ndash;23.\u003c/li\u003e\n\u003cli\u003eD.W. Gandy, C. Stover, K. Bridger, S. 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Busby, Formulating the strength factor \u0026alpha; for improved predictability of radiation hardening, Journal of Nuclear Materials 465 (2015) 724\u0026ndash;730. https://doi.org/https://doi.org/10.1016/j.jnucmat.2015.07.009.\u003c/li\u003e\n\u003cli\u003eG.E. Lucas, The evolution of mechanical property change in irradiated austenitic stainless steels, Journal of Nuclear Materials 206 (1993) 287\u0026ndash;305. https://doi.org/https://doi.org/10.1016/0022-3115(93)90129-M.\u003c/li\u003e\n\u003cli\u003eR.E. Stoller, S.J. Zinkle, On the relationship between uniaxial yield strength and resolved shear stress in polycrystalline materials, Journal of Nuclear Materials 283\u0026ndash;287 (2000) 349\u0026ndash;352. https://doi.org/https://doi.org/10.1016/S0022-3115(00)00378-0.\u003c/li\u003e\n\u003cli\u003eF. Kroupa, P.B. Hirsch, Elastic interaction between prismatic dislocation loops and straight dislocations, Discuss Faraday Soc 38 (1964) 49\u0026ndash;55.\u003c/li\u003e\n\u003cli\u003eJ. Tucker, E. Marquis, B. Spencer, G. Burke, Modeling and validation of irradiation damage in ni-based alloys for long-term lwr applications, Oregon State Univ., Corvallis, OR (United States), 2019.\u003c/li\u003e\n\u003cli\u003eF. Teng, D.J. Sprouster, G.A. Young, J.-H. Ke, J.D. Tucker, Effect of stoichiometry on the evolution of thermally annealed long-range ordering in Ni\u0026ndash;Cr alloys, Materialia (Oxf) 8 (2019) 100453. https://doi.org/https://doi.org/10.1016/j.mtla.2019.100453.\u003c/li\u003e\n\u003cli\u003eD.P. Guillen, J.P. Wharry, G.K. Housley, C.D. Hale, J. V Brookman, D.W. Gandy, Experiment design for the neutron irradiation of PM-HIP alloys for nuclear reactors, Nuclear Engineering and Design 402 (2023) 112114.\u003c/li\u003e\n\u003cli\u003eJ.P. Wharry, C.D. Clement, Y. Zhao, K. Baird, D. Frazer, J. Burns, Y. Lu, Y. Wu, C. Knight, D.P. Guillen, Mechanical testing data from neutron irradiations of PM-HIP and conventionally manufactured nuclear structural alloys, Data Brief 48 (2023) 109092.\u003c/li\u003e\n\u003cli\u003eC.M. Parish, K.G. Field, A.G. Certain, J.P. Wharry, Application of STEM characterization for investigating radiation effects in BCC Fe-based alloys, J Mater Res 30 (2015) 1275\u0026ndash;1289.\u003c/li\u003e\n\u003cli\u003eP. Xiu, Y.N. Osetsky, L. Jiang, G. Velisa, Y. Tong, H. Bei, W.J. Weber, Y. Zhang, L. Wang, Dislocation loop evolution and radiation hardening in nickel-based concentrated solid solution alloys, Journal of Nuclear Materials 538 (2020) 152247.\u003c/li\u003e\n\u003cli\u003eK.G. Field, S.A. Briggs, K. Sridharan, Y. Yamamoto, R.H. Howard, Dislocation loop formation in model FeCrAl alloys after neutron irradiation below 1 dpa, Journal of Nuclear Materials 495 (2017) 20\u0026ndash;26.\u003c/li\u003e\n\u003cli\u003eM.J. Swenson, J.P. Wharry, The comparison of microstructure and nanocluster evolution in proton and neutron irradiated Fe\u0026ndash;9% Cr ODS steel to 3 dpa at 500 C, Journal of Nuclear Materials 467 (2015) 97\u0026ndash;112.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-advanced-manufacturing","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [npj Advanced Manufacturing](https://www.nature.com/npjadvmanuf/)","snPcode":"44334","submissionUrl":"https://submission.springernature.com/new-submission/44334/3","title":"npj Advanced Manufacturing","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Alloy 625, Alloy 690, Powder Metallurgy Hot Isostatic Pressing (PM-HIP), Neutron irradiation, Mechanical behaviour","lastPublishedDoi":"10.21203/rs.3.rs-8157703/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8157703/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis work presents a systematic and comprehensive investigation of neutron irradiation effects on Ni-based alloys manufactured by powder metallurgy with hot isostatic pressing (PM-HIP) compared to their conventional forged counterparts. PM-HIP is a leading candidate to replace forging as a manufacturing method for structural components in future nuclear reactors due to its more homogeneous microstructures and superior mechanical properties. However, such components can be exposed to elevated temperature irradiation in service, which will significantly alter material performance. Understanding PM-HIP material performance as compared to conventional forgings under realistic reactor operating conditions is therefore essential for certification and deployment. In this study, Ni-based Alloys 625 and 690 are investigated under neutron irradiation at target damage levels of ~\u0026thinsp;1 and ~\u0026thinsp;3 dpa, allowing for direct comparisons between PM-HIP manufacturing and forging. Uniaxial tensile tests evaluate the irradiation-induced changes in mechanical behaviour, while the irradiation-induced microstructural changes are investigated using transmission electron microscopy and atom probe tomography. Overall, PM-HIP Alloy 625 presents superior mechanical properties (e.g., less irradiation hardening, smaller reduction in ductility) compared to forged Alloy 625 under irradiation. This is primarily attributed to the fact that PM-HIP Alloy 625 has an order-of-magnitude lower void population than that observed in the forged counterpart at all damage levels due to its lower initial dislocation density. On the other hand, minimal differences in irradiation-induced microstructures are observed between PM-HIP and forged Alloy 690, resulting in suppressed differences in mechanical properties between them at corresponding damage levels. These findings consistently demonstrate comparable or greater irradiation tolerance in PM-HIP Alloy 625 and 690 than in their forged counterparts, providing crucial data to support the qualification of PM-HIP manufacturing of Ni-based alloys for future generation nuclear structural components.\u003c/p\u003e","manuscriptTitle":"Effects of Neutron Irradiation on Ni-Based Alloys: A Comparative Study Between PM-HIP and Forging","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-01 14:47:01","doi":"10.21203/rs.3.rs-8157703/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-02-23T18:17:21+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-21T09:07:53+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-18T12:48:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"279371967333891151011431067726164558966","date":"2026-02-09T20:10:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"44327539280078930914274681196698829117","date":"2026-01-22T12:20:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"114828028000613862543133937811368409378","date":"2025-12-19T13:50:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-14T00:19:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"177415019877007805104782092689484791257","date":"2025-12-03T21:02:46+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-25T23:07:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-24T10:02:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-24T03:36:42+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Advanced Manufacturing","date":"2025-11-19T17:16:07+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-advanced-manufacturing","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [npj Advanced Manufacturing](https://www.nature.com/npjadvmanuf/)","snPcode":"44334","submissionUrl":"https://submission.springernature.com/new-submission/44334/3","title":"npj Advanced Manufacturing","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c92d5589-7231-4098-b0bf-47e04434ece3","owner":[],"postedDate":"December 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":58630704,"name":"Physical sciences/Engineering"},{"id":58630705,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-03-12T16:53:53+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-01 14:47:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8157703","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8157703","identity":"rs-8157703","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}