Insights into Microstructure Evolution and Mechanical Properties of Linear friction welding of Dissimilar Ti2AlNb and Ti60 Alloys

Insights into Microstructure Evolution and Mechanical Properties of Linear friction welding of Dissimilar Ti2AlNb and Ti60 Alloys | 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 Research Article Insights into Microstructure Evolution and Mechanical Properties of Linear friction welding of Dissimilar Ti2AlNb and Ti60 Alloys Jiaying Li, Tiejun Ma, Hongbo Zhang, Xiawei Yang, Wenya Li, Achilles Vairis This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8204363/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract In this study, microstructure evolution and the interface metallurgical bond of linear friction welded dissimilar Ti 2 AlNb/Ti60 joint were studied. The relationship of microstructure to tensile and impact strength of the joint were analyzed. Results show that continuous dynamic recrystallization occurred on two weld zones (WZ) during welding, forming equiaxed fine grains which were smaller than those of the two base metals. On the Ti60 side thermo-mechanically affected zone, α grains were elongated under the high temperature and shear force effects; while on the Ti 2 AlNb side, the large B2 grains were also elongated where a large number of O phases were dissolved. In the Ti 2 AlNb side heat affected zone, the B2 grains were not deformed, and the O phases inside B2 grains were decomposed, as the welding temperature was lower than that in the TMAZ. The interface metallurgical bond was achieved through mutual diffusion of Ti, Al and Nb, producing an element transition layer of 1.54 µm composed of TiAl 3 and NbAl 3 intermetallic compounds. The tensile strength of the joint was 920 MPa, which is 97.9% of the Ti60 BM, but elongation was 1.7%. Failure of joint during tensile strength testing was located at the junction of Ti 2 AlNb side TMAZ and HAZ, where the O phases dissolve and there was no dynamic recrystallization of the B2 grains. So, the plastic deformation of the joint when a tensile load was applied was concentrated there, producing limited elongation. The impact energy at interface was measured to be 13.0 J/cm², which is higher than that of Ti 2 AlNb BM, as the toughness of the interface is better than that of Ti 2 AlNb BM, which is related to TiAl 3 and NbAl 3 intermetallic compounds forming at the interface element transition layer. linear friction welding Ti2AlNb Ti60 dissimilar joint interface microstructure tensile strength impact strength Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction The Ti 2 AlNb and Ti60 alloys are two alternative materials to the nickel-based superalloys which are used to produce blisks in advanced aero-engines [ 1 , 2 ]. The Ti 2 AlNb alloy is lightweight high-temperature material of the Ti-Al system alloy, suitable to use at 650°C [ 3 ]. The Ti60 titanium alloy is a near-α type high-temperature titanium alloy with service temperature between 400°C and 600°C [ 4 ], with good specific strength and fatigue behavior. In the future, Ti 2 AlNb/Ti60 dual-alloy blisks could be used in advanced aero-engine compressors [ 5 ]. Linear friction welding is the optimal manufacturing technique to produce dual-alloy blisks [ 6 , 7 ]. It is a solid-state process where there is no molten weld pool formed, therefore solidification defects do not develop; or there are no requirements to use protective gases or require filler material. To date, linear friction welding has been successfully used in the production of aero-engine blisks by a number of manufacturers [ 8 ], with Rolls Royce, MTU Aero Engines, General Electric and Pratt & Whitney producing blisks of titanium alloys for aeroengine compressors. There is limited research published on linear friction welding Ti60 alloy similar material joints or Ti 2 AlNb alloy similar material joints. Guo et al. [ 9 ] have developed numerical models of the temperature of Ti60 alloy joints and studied phase transformations, dynamic recrystallization and texture evolution of such joints. Due to the fine grain and precipitation strengthening in the weld zone, the tensile strength of the joint (943 MPa) is higher than that of the base material (914 MPa). Chen et al. [ 10 – 12 ] have investigated in detail Ti 2 AlNb alloy joints, including microstructural evolution, mechanical properties and hot corrosion behavior, together with effects of post-weld solution and aging treatments. It was found that the weld zone consisted of B2 matrix and residual O phase. Following aging treatment, acicular O phase precipitated, which significantly increased microhardness and tensile strength. There is a single published work on Ti 2 AlNb/Ti60 dissimilar materials joint [ 13 ], where the interface microstructure evolution was studied. The joint developed was associated to continuous dynamic recrystallization on both sides of the interface during the steady state frictional phase with temperature exceeding the transformation temperatureα→β. But, this work did not investigate the microstructure evolution in other areas of the joint and the effects of microstructure characteristics on mechanical properties. Therefore, the microstructure evolution is investigated in detail in this study, using optical microscopy (OM), scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) equipped with energy dispersive spectroscopy (EDS). In addition, the effects of microstructure on tensile and impact strength were investigated. The aim of this research is to provide further joint material data useful for the production of Ti 2 AlNb-Ti60 dual-alloy blisks for advanced aero-engine compressors. 2. Materials and Methods 2.1 Materials The Ti 2 AlNb alloy used in this study was produced by the Northwest Institute for Nonferrous Metal Research of China, and its chemical composition is shown in Table 1 , where Al and Nb are the main alloying elements. Table 1 Chemical composition of Ti 2 AlNb alloy Elements Ti Al Nb O N H wt.% Balance 11.5 38.1 0.066 0.018 0.003 The near-alpha Ti60 titanium alloy used in this study was also provided by the Northwest Institute for Nonferrous Metal Research, and its chemical composition is shown in Table 2 . Compared to the Ti 2 AlNb alloy, it contains fewer alloying elements. Table 2 Chemical composition of Ti60 alloy Elements Ti Sn Zr Si Mo Nd Al wt.% Balance 4.0 3.5 0.4 1.0 0.85 5.5 2.2 Welding The linear friction welding was carried out with the XMH-250 machine developed at the Shaanxi Provincial Key Laboratory of Friction Welding of the Northwestern Polytechnical University in China. The dimensions of the welding specimens were 12 mm × 22 mm × 60 mm, while the welding interface had dimensions of 12 mm × 22 mm. The sinusoidal reciprocating movement is along the 22 mm direction of the specimen. During welding, the Ti 2 AlNb specimen is placed at the oscillating chuck, as it would have been the blade in a blisk; and the Ti60 specimen is located at the stationary chuck, as it would have been the disk in a blisk. The welding parameters used in this study are shown in Table 3 . Table 3 Linear friction welding parameters Amplitude of oscillation (mm) Frequency of oscillation (Hz) Time (s) Friction pressure (MPa) 2 25 6 70 2.3 Microstructure and mechanical property measurment Following welding, metallographic, tensile and impact strength specimens were cut from the joint, and their relative position in the joint is shown in Fig. 1 . The metallographic specimen was polished with an MP-1B polishing machine and etched using Kroll’s reagent (0.5 vol% HF + 1.5 vol% HNO3 + 2 vol% HCl + 96 vol% H 2 O). Then, an optical microscope (OM) (OLYMPUS PMG3) and a scanning electron microscope (SEM) (Helios G4 CX) were used to investigate the microstructure evolution in the joint. The electron back-scattering diffraction (EBSD) analysis was also conducted. The EBSD specimen was ground and polishede, and then electro-polished in a solution (30 vol% C 4 H 9 OH + 64 vol% CH 3 OH + 6 vol% HClO 4 ) at a voltage of 20 V for 80 s at 0 ℃. The EBSD analysis was performed in the SEM with Oxford EBSD data acquisition software (HKL-Channel 5). In addition, the interface bond mechanism was investigated by cutting a thin lamella at the interface using the focused ion beam (FIB) lift-out technique, and studying the specimen with a high-resolution transmission electron microscope (TEM) (FEI Talos F200X). The tensile strength specimens were prepared according to the GB/T 228.1–2002 standard and tested at a crosshead speed of 1 mm/min. After the test, the SEM was used to study the fracture surface of the tensile strength specimens. The impact strength specimens with a U-shaped groove were prepared following the GB/T 229–1994 standard, and the fracture surface was studied with SEM as well. The phase composition of the impact fracture surface was studied with X-Ray Diffraction (XRD) equipment. 3. Results 3.1 Microstructure and its evolution 3.1.1 Macrostructure of the joint The low magnification photo of the interface macrostructure along the direction of oscillation is shown in Fig. 2 , where the joint can be divided into seven zones: Ti60 side base material zone (BM), Ti60 side thermo-mechanically affected zone (TMAZ), Ti60 side weld zone (WZ), Ti 2 AlNb side WZ, Ti 2 AlNb side TMAZ, Ti 2 AlNb side heat affected zone (Ti 2 AlNb HAZ), and Ti 2 AlNb side BM. The width of Ti60 side TMAZ together with itse WZ is approximately 1000 µm. Compared with the Ti60 side BM, grains at the Ti60 side TMAZ are severely deformed and elongated along the oscillating interface. The microstructure of the Ti60 side WZ is dense and uniform, while the Ti60 BM cannot be identified. The width of the WZ together with the TMAZ on the Ti 2 AlNb side is approximately 1500 µm, larger than that on the Ti60 side joint. There is developed a wide HAZ between Ti 2 AlNb side TMAZ and the BM. This can be attributed to that large B2 grains(as shown in Figs. 2 and 3 a) of Ti 2 AlNb exhibits good thermal strength, with small plastic deformation and weak plastic flow during welding, resulting in less heat being carried away by the flash. The heat conduction influence range on Ti 2 AlNb side joint is larger, ultimately developing a wider HAZ between the TMAZ and BM on the Ti 2 AlNb side joint. The heat-affected zone is affected by heat conducted away and to lesser extent by the stress state, with large B2 grains showing minimal deformation similar as BM. 3.1.2 Microstructure evolution in different zones of joint Figure 3 shows the SEM microstructure in each zone of the joint. Figure 3 a shows that of Ti60 BM, which consists of a large number of equiaxed α, with β phases distributed at α boundaries. The size of the α phase grains is greater than 20 µm. There are few titanium silicides scattered at the α grain boundaries, which can pin grain boundaries and improve thermal stability of Ti60 [ 14 ]. Figure 3 c shows the SEM microstructure of the Ti60 side TMAZ, where α grains are elongated and deformed. The white β at the α grain boundaries retains its original state, but silicides at the α grain boundaries have disappeared. This is related to welding, where material is affected by the combined effects of high temperatures and large shear forces, which deform equiaxed α grains, while silicides at grain boundaries decompose due to heat. However, since equiaxed α still remains, it can be deduced that temperature at the Ti60 side TMAZ does not exceed the β-transus temperature (of 1050°C [ 15 ]). Figure 3 e shows the SEM microstructure of the Ti60 side WZ, which consists of undeformed fine grains smaller than those of BM, and the silicide in the Ti60 BM having disappear. The average grain size of WZ is 5.7 µm, which is significantly finer than that in the base material, as dynamic recrystallization took place during welding. In the published study [ 16 ] it was shown that during LFW of titanium alloys temperatures exceed 1200°C, and the complete α → β transformation will occurs in WZ, forming uniform high-temperature β phase. At the same time, due to thermal-mechanical coupling, temperatures exceeded 1200°C as dynamic recrystallization occurred in this area due to increased cooling rates, the αˊ martensite is precipitating from the β phase, since Ti60 is a near-α titanium alloy with β-stabilizing elements [ 17 ] . Figure 3 b shows the SEM microstructure of Ti 2 AlNb BM, where the B2 grain size is larger than that of the α grains in the Ti60 BM, with numerous needle O phase grains inside B2 grains and at grain boundaries. Figure 3 d shows the SEM microstructure of the Ti 2 AlNb HAZ, with a few needle O phase grains inside the B2 grains in HAZ decomposing and dissolving into the B2 matrix. Figure 3 f shows the SEM microstructure of the Ti 2 AlNb TMAZ, with significant degree of O phase dissolution. In addition, due to the large grain size of Ti 2 AlNb, it is difficult to study TMAZ grains with high-magnification SEM. So, EBSD characterization was used for the Ti 2 AlNb side TMAZ, as shown in Fig. 4 . The low-magnification inverse phase figure (IPF) (Fig. 4 a) shows the B2 grains to be elongated and deformed due to high temperatures and stresses developed during welding. From the high-magnification IPF image (Fig. 4 b), it can be seen that dynamic recrystallization of B2 grains occurred in the TMAZ near the WZ, producing randomly oriented recrystallized B2 grains of smaller size than those in the BM. The SEM microstructure of the Ti 2 AlNb WZ is shown in Fig. 3 g, where there exists single B2 phase, and the needle O phase grains of BM have dissolved completely. The WZ consists of equiaxed B2 grains that are much smaller than those in the BM, with a size of 5–10 microns, as complete B2 dynamic recrystallization did occur, which suggests that the interface temperature exceeded the transformation temperature of O of titanium alloys[ 18 ]. As the temperature increases during welding, the O phase on the Ti 2 AlNb side WZ quickly and completely transforms into high-temperature B2 phase. At the same time, under high strain rate deformation in the WZ, dynamic recrystallization of B2 phase take places, to form equiaxed B2 grains of smaller size than those in the BM. When welding is stopped, the cooling rate reaches up to 300 k/s [ 19 ], which exceeds the critical cooling rate for B2→O transformation to occur. So, the Ti 2 AlNb side WZ is uniformly composed of B2 phase grains. In this study, dynamic recrystallization took place on both sides of the WZs. The recrystallization distribution of WZ on both sides of the joint was investigated, as shown in Fig. 5 . The WZ on the Ti60 side contains a larger number of blue recrystallized grains together with a large number of yellow subgrains (see Fig. 5 a); similarly, the Ti 2 AlNb side WZ also contains a large number of subgrains. So, it can be deduced that the recrystallization processes of WZ on both sides of the joint is accompanied with subgrains. Previous published research [ 9 ] has shown that in the case of high stacking fault energy Ti-based alloys, subgrains form during recrystallization, which is typical of continuous dynamic recrystallization. 3.1.3 Interface microstructure and bonding mechanism Figure 6 a shows the SEM microstructure of the interface, where the Ti60 side consists of dense acicular structures, and there are no recrystallization grain boundaries. The temperature on the Ti60 side exceeded the β-transus temperature (of 1050°C [ 15 ]), which produces high-temperature β grains and produces fine recrystallized grains by dynamic recrystallization. It was followed by dense henlized grais which formed inside recrystallized grains during the quick cooling stage once welding finished. Due to the high content of β elements at the interface in Ti 2 AlNb, the Ti 2 AlNb side interface consisted of a uniform B2 phase in the joint, as shown in Fig. 6 a. It can also be clearly observed from Fig. 6 a that the αˊon Ti60 side of interface grows into the B2 phase on the Ti 2 AlNb side interface. The low-magnification bright-field image of the interface is shown in Fig. 6 b. The left side of Fig. 6 b is Ti60, where numerous tiny acicular αˊ can be seen; while the right side where Ti 2 AlNb is placed, there are B2 recrystallized grains. The blue framed detail in Fig. 6 b included the B2 recrystallized grain, and it is enlarged in Fig. 6 c. The grain was analyzed using selected area electron diffraction (SAED) and compared to standard patterns [ 20 ], which showed that the B2 grain has a body-centered cubic [001] pattern, as the crystal zone axes are parallel to the [001] direction, as shown in Fig. 6 d. Figure 6 e shows the high-angle annular dark field (HAADF) image of the interface, and the EDS line scan is shown in Fig. 6 f. The latter shows that Ti diffuses from the Ti60 side to the Ti 2 AlNb side at the interface, while Al and Nb from the Ti 2 AlNb side diffuse toward the Ti60 side. The width of the diffusion layer is 1.54 µm. Previous studies investigating the forming mechanism of such cases [ 21 ] have shown that high pressure and large deformations can eliminate crystal lattice defects at the join interface, allowing for mutual diffusion of interfacial elements. It enhances the interatomic bonding force and increases the joint strength. Although LFW has a bery short duration, there exist similarities with diffusion welding at high pressure and large deformations. In addition, lattice distortions, dislocations, and vacancies produced by intense plastic deformation reduce the activation energy necessary for diffusion. This lets interface elements to diffuse in a short time, which eliminates the original Ti 2 AlNb/Ti60 interface and develops of a new joined interface. From the SEM and TEM observations, the bond process at the Ti 2 AlNb/Ti60 interface during LFW can be summarized as follows: during welding the interface evolves into a phase boundary between the β and B2 phases at high temperatures. The β and B2 phases have identical crystal structures (both body-centered cubic structure), but their elemental compositions are of their parent materials. Under the combined effect of high temperature and large stresses during LFW, alloy elements in the high-temperature β phase on the Ti60 side and the high-temperature B2 phase on the Ti 2 AlNb side diffuse mutually. The original interface disappears, and an element transition layer of 1.54 µm thickness is formed between the two phases. After quick cooling, acicular αˊ martensite precipitates on the Ti60 side interface, while Ti 2 AlNb had no precipitated phase and retained the B2 phase. The αˊ on the Ti60 side interface grows into B2 grains on the Ti 2 AlNb side. This process is responsible for metallurgical bond of the joint. 3.2 Mechanical properties of joints 3.2.1 Tensile strength The tensile strength test results of joint are shown in Table 4 . The yield and ultimate tensile strength of the joint were 878 MPa and 920 MPa, respectively, which are equivalent to those of the Ti60 BM. The elongation of the joint was 1.7%, due to limited plasticity of the joint. After the tensile strength measurement, the specimens are shown in Fig. 7 , where the location of fracture is close to the interface, with no obvious neck formed, confirming further the limited plasticity of the joint. A metallographic specimen from the fracture location was prepared and studied with OM, as shown in Fig. 8 . Fracture was located at approximately 1500 µm away from the interface on the Ti 2 AlNb side of the joint, at the boundary of TMAZ and HAZ. Analysis shows that the strengthening phase O grains in the TMAZ and HAZ of the Ti 2 AlNb side joint have dissolved, which allows for failure due to localized plastic strain concentration during tensile loading [ 22 ]. But, complete dynamic recrystallization takes place in WZ, and forms a large number of recrystallized B2 grains which are significantly smaller than those in the BM, which has a strengthening effect. At the Ti60 side joint, whose BM grain size is smaller than that of Ti 2 AlNb’s BM, there is no α strengthening phase dissolution during welding, and the mechanical strength of this side joint is higher than that of the TMAZ and HAZ of the Ti 2 AlNb side joint. In addition, the interface bond strength was higher than that of the HAZ and TMAZ of the Ti 2 AlNb side joint, as even though the Ti60 and Ti 2 AlNb alloys had differences in composition and structure, there developed sound interface metallurgical bond. Plastic deformation during tensile testing was primarily in the TMAZ and HAZ of the Ti 2 AlNb side joint, elongation of the joint is lower than that of the Ti 2 AlNb BM, at 1.7%. Table 4 Tensile strength measurements Specimen Yield strength (MPa) Tensile strength (MPa) Elongation (%) Joint 878 920 1.7 Ti60 BM 876 941 13.1 Ti 2 AlNb BM 1160 1217 2.6 In order to investigate further fracture, fracture surface was studied using SEM, as shown in Fig. 9 . The fracture surface is uneven (see Fig. 9 a), with no obvious shear lip, and shows brittle fracture characteristics. Figure 9 b is an detailed view of area A in Fig. 9 a, where there are river-like patterns. In the further detailed view of Fig. 9 c, cleavage steps and shallow dimples can be seen. Figure 9 d is a detailed view of area B, where it can be seen that a large number of ductile dimples. Overall, the fracture surface of the joint exhibits quasi-cleavage fracture characteristics [ 23 ]. 3.2.3 Impact strength The impact strength measurement results are shown in Table 5 . The impact toughness of the Ti60 BM (15.1 J/cm²) is higher than that of the Ti 2 AlNb BM (6.6 J/cm²), and the impact toughness of the joint (13.0 J/cm²) is also higher than that of the Ti 2 AlNb BM. Figure 10 shows the impact strength specimens following the measurement, where all specimens broke at the notch, and fracture paths were terminology, as the interface has high impact toughness. Table 5 Impact toughness of joint Specimen Impact toughness (J/cm 2 ) Joint 13.0 Ti60 BM 15.1 Ti 2 AlNb BM 6.6 The fracture surface of the specimen is shown in Fig. 11 . Figure 11 b shows a detailed view of fracture surface of the red frame in Fig. 11 a, where the fracture surface is smooth. The notch is at the bottom edge of the fracture surface in this figure, with crack initiating from the notch center. The fracture surface contains numerous dimples (see Fig. 11 b), which confirms experimental result where impact toughness of joint interface is high. The XRD measurement was taken at the impact fracture surface (see Fig. 12 ), which identified TiAl 3 and NbAl 3 intermetallic compounds. As was shown in Section 3.1.3 , the metallurgical bond of the joint interface is achieved through mutual diffusion of metals during welding, which develops a 1.54 µm transition layer. The XRD analysis of fractured interface showed limited TiAl 3 and NbAl 3 intermetallic compounds, which are the reason that the interface impact toughness is not lower than that of the Ti 2 AlNb BM. 4. Conclusion The following conclusions can be made: (1) Continuous dynamic recrystallization occurs on both sides of the joint interface, forming fine equiaxed grains with smaller size than those of the BMs. Under the combined effects of high temperatures and large shear forces during welding, the microstructure of Ti60 TMAZ is elongated. On the Ti 2 AlNb side TMAZ, the large B2 grains become also elongated, and B2 dynamic recrystallization occurs in the TMAZ near the WZ. In addition, the O phases within the B2 grains are dissolved in this zone; the Ti 2 AlNb side HAZ is mainly effected by heat during welding, so B2 grains are not deformed. The O phases within the B2 grains in HAZ undergo limited decomposition, as the temperature at the HAZ is lower than that of the TMAZ. (2) The interface undergoes a transformation from the original friction interface → the β/B2 phase interface at quasi-steady friction stage → the αˊ/B2 phase interface after quick cooling at the end of welding, with acicular αˊ on the Ti60 side interface growing into B2 martix on the Ti 2 AlNb side interface, which removes the initial interface. In addition, the combined effect of high temperatures and stresses together with large deformations during welding, there is adequate diffusion of Ti, Al, and Nb on both sides of the interface. This develops a diffusion layer of 1.54 microns thickness with the intersolute elements, which is the main mechanism for the interface metallurgical bond. (3) The tensile strength of joint is 920 MPa, which is 97.9% of the Ti60 BM, with elongation of 1.7%. The failure zone of the joint is located at the interface between the TMAZ and HAZ on the Ti 2 AlNb side joint. This is because the strengthening O phases dissolve extensively in this zone, with no dynamic recrystallization occuring to allow for fine grain strengthening effect. The impact strength energy of the joint interface is 13.0 J/cm², higher than that of the Ti 2 AlNb BM, as the interface shows improved toughness compared to the Ti 2 AlNb BM. This is associated to the formation of intermetallic compounds including TiAl 3 and NbAl 3 at the interface diffusion layer. Declarations Declaration of competing interest The authors declare that there are no competing financial interests or personal relationships that could influence the work reported in this paper. Fundings This work was supported by the National Natural Science Foundation of China (grant no. 52105400) and Heilongjiang Advanced Friction Welding Technology and Equipment Key Laboratory (grant no. 2025001).. Author contributions Jiaying Li: Investigation, Methodology, Writing original draft. Tiejun Ma: Methodology, Writing–review & editing Resources. Hongbo Zhang: Formal analysis. Xiawei Yang: Investigation. Wenya Li: Formal analysis. Achilles Vairis: Formal analysis, Writing–review. Acknowledgements This work was supported by the National Natural Science Foundation of China (grant no. 52105400) and Heilongjiang Advanced Friction Welding Technology and Equipment Key Laboratory (grant no. 2025001).. Data availability The processed data required to reproduce these findings cannot be shared at this time as data are part of a larger ongoing study. References Li SQ, Mao Y, Znang JW et al (2002) Effect of microstructure on tensile properties and fracture behavior of intermetallic Ti 2 AlNb alloys. Trans Nonferrous Met Soc China 12(4):582–586 Peng W, Zeng W, Wang Q et al (2014) Effect of processing parameters on hot deformation behavior and microstructural evolution during hot compression of as-cast Ti60 titanium alloy. 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8","display":"","copyAsset":false,"role":"figure","size":792357,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of fracture location after tensile strength measurement (OM)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8204363/v1/791e5084a0eb1ce6300c1f30.png"},{"id":99307417,"identity":"446bd963-12ff-4e49-9bb7-4b9c69e1c52d","added_by":"auto","created_at":"2025-12-31 16:06:14","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1076764,"visible":true,"origin":"","legend":"\u003cp\u003eFracture surface of tensile strength specimen: (a) macroscopic morphology, (b) low magnification image of area A, (c) high magnification image of area A, (d) area B\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8204363/v1/349db42e17be1b54438a940e.png"},{"id":98816726,"identity":"72a919ac-fa0c-419b-a4c7-f4c06334752d","added_by":"auto","created_at":"2025-12-22 16:26:51","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":191870,"visible":true,"origin":"","legend":"\u003cp\u003eImpact strength specimens\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8204363/v1/660ce64a1074daf71a5c2eba.png"},{"id":99307396,"identity":"c7ded5d7-91e3-4298-aa91-cc21c782075a","added_by":"auto","created_at":"2025-12-31 16:06:12","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":535637,"visible":true,"origin":"","legend":"\u003cp\u003eFracture surface of impact strength specimen: (a) overall morphology, (b) detail\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8204363/v1/7945296e89692e06990e9763.png"},{"id":98816733,"identity":"a73a6093-8e66-41a6-bf62-af05ce25a8ea","added_by":"auto","created_at":"2025-12-22 16:26:51","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":69206,"visible":true,"origin":"","legend":"\u003cp\u003eXRD of impact fracture\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-8204363/v1/832776177fba77ec87666604.png"},{"id":101942761,"identity":"dda66c31-351a-4bf4-804f-9c249046777a","added_by":"auto","created_at":"2026-02-05 09:37:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7901077,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8204363/v1/aebd252d-bd67-4613-a994-2e64aa8a66f8.pdf"}],"financialInterests":"","formattedTitle":"Insights into Microstructure Evolution and Mechanical Properties of Linear friction welding of Dissimilar Ti2AlNb and Ti60 Alloys","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe Ti\u003csub\u003e2\u003c/sub\u003eAlNb and Ti60 alloys are two alternative materials to the nickel-based superalloys which are used to produce blisks in advanced aero-engines [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloy is lightweight high-temperature material of the Ti-Al system alloy, suitable to use at 650\u0026deg;C [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The Ti60 titanium alloy is a near-α type high-temperature titanium alloy with service temperature between 400\u0026deg;C and 600\u0026deg;C [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], with good specific strength and fatigue behavior. In the future, Ti\u003csub\u003e2\u003c/sub\u003eAlNb/Ti60 dual-alloy blisks could be used in advanced aero-engine compressors [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eLinear friction welding is the optimal manufacturing technique to produce dual-alloy blisks [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. It is a solid-state process where there is no molten weld pool formed, therefore solidification defects do not develop; or there are no requirements to use protective gases or require filler material. To date, linear friction welding has been successfully used in the production of aero-engine blisks by a number of manufacturers [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], with Rolls Royce, MTU Aero Engines, General Electric and Pratt \u0026amp; Whitney producing blisks of titanium alloys for aeroengine compressors.\u003c/p\u003e \u003cp\u003eThere is limited research published on linear friction welding Ti60 alloy similar material joints or Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloy similar material joints. Guo et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] have developed numerical models of the temperature of Ti60 alloy joints and studied phase transformations, dynamic recrystallization and texture evolution of such joints. Due to the fine grain and precipitation strengthening in the weld zone, the tensile strength of the joint (943 MPa) is higher than that of the base material (914 MPa). Chen et al. [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] have investigated in detail Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloy joints, including microstructural evolution, mechanical properties and hot corrosion behavior, together with effects of post-weld solution and aging treatments. It was found that the weld zone consisted of B2 matrix and residual O phase. Following aging treatment, acicular O phase precipitated, which significantly increased microhardness and tensile strength. There is a single published work on Ti\u003csub\u003e2\u003c/sub\u003eAlNb/Ti60 dissimilar materials joint [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], where the interface microstructure evolution was studied. The joint developed was associated to continuous dynamic recrystallization on both sides of the interface during the steady state frictional phase with temperature exceeding the transformation temperatureα\u0026rarr;β. But, this work did not investigate the microstructure evolution in other areas of the joint and the effects of microstructure characteristics on mechanical properties.\u003c/p\u003e \u003cp\u003eTherefore, the microstructure evolution is investigated in detail in this study, using optical microscopy (OM), scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) equipped with energy dispersive spectroscopy (EDS). In addition, the effects of microstructure on tensile and impact strength were investigated. The aim of this research is to provide further joint material data useful for the production of Ti\u003csub\u003e2\u003c/sub\u003eAlNb-Ti60 dual-alloy blisks for advanced aero-engine compressors.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eThe Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloy used in this study was produced by the Northwest Institute for Nonferrous Metal Research of China, and its chemical composition is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, where Al and Nb are the main alloying elements.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloy\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElements\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNb\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eH\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ewt.%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBalance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e38.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.066\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.003\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 near-alpha Ti60 titanium alloy used in this study was also provided by the Northwest Institute for Nonferrous Metal Research, and its chemical composition is shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Compared to the Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloy, it contains fewer alloying elements.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of Ti60 alloy\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElements\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eZr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNd\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ewt.%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBalance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Welding\u003c/h2\u003e \u003cp\u003eThe linear friction welding was carried out with the XMH-250 machine developed at the Shaanxi Provincial Key Laboratory of Friction Welding of the Northwestern Polytechnical University in China. The dimensions of the welding specimens were 12 mm \u0026times; 22 mm \u0026times; 60 mm, while the welding interface had dimensions of 12 mm \u0026times; 22 mm. The sinusoidal reciprocating movement is along the 22 mm direction of the specimen. During welding, the Ti\u003csub\u003e2\u003c/sub\u003eAlNb specimen is placed at the oscillating chuck, as it would have been the blade in a blisk; and the Ti60 specimen is located at the stationary chuck, as it would have been the disk in a blisk. The welding parameters used in this study are shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLinear friction welding 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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAmplitude of oscillation (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFrequency of oscillation\u003c/p\u003e \u003cp\u003e(Hz)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTime\u003c/p\u003e \u003cp\u003e(s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFriction pressure (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Microstructure and mechanical property measurment\u003c/h2\u003e \u003cp\u003eFollowing welding, metallographic, tensile and impact strength specimens were cut from the joint, and their relative position in the joint is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The metallographic specimen was polished with an MP-1B polishing machine and etched using Kroll\u0026rsquo;s reagent (0.5 vol% HF\u0026thinsp;+\u0026thinsp;1.5 vol% HNO3\u0026thinsp;+\u0026thinsp;2 vol% HCl\u0026thinsp;+\u0026thinsp;96 vol% H\u003csub\u003e2\u003c/sub\u003eO). Then, an optical microscope (OM) (OLYMPUS PMG3) and a scanning electron microscope (SEM) (Helios G4 CX) were used to investigate the microstructure evolution in the joint. The electron back-scattering diffraction (EBSD) analysis was also conducted. The EBSD specimen was ground and polishede, and then electro-polished in a solution (30 vol% C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eOH\u0026thinsp;+\u0026thinsp;64 vol% CH\u003csub\u003e3\u003c/sub\u003eOH\u0026thinsp;+\u0026thinsp;6 vol% HClO\u003csub\u003e4\u003c/sub\u003e) at a voltage of 20 V for 80 s at 0 ℃. The EBSD analysis was performed in the SEM with Oxford EBSD data acquisition software (HKL-Channel 5). In addition, the interface bond mechanism was investigated by cutting a thin lamella at the interface using the focused ion beam (FIB) lift-out technique, and studying the specimen with a high-resolution transmission electron microscope (TEM) (FEI Talos F200X).\u003c/p\u003e \u003cp\u003eThe tensile strength specimens were prepared according to the GB/T 228.1\u0026ndash;2002 standard and tested at a crosshead speed of 1 mm/min. After the test, the SEM was used to study the fracture surface of the tensile strength specimens. The impact strength specimens with a U-shaped groove were prepared following the GB/T 229\u0026ndash;1994 standard, and the fracture surface was studied with SEM as well. The phase composition of the impact fracture surface was studied with X-Ray Diffraction (XRD) equipment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Microstructure and its evolution\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Macrostructure of the joint\u003c/h2\u003e \u003cp\u003eThe low magnification photo of the interface macrostructure along the direction of oscillation is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, where the joint can be divided into seven zones: Ti60 side base material zone (BM), Ti60 side thermo-mechanically affected zone (TMAZ), Ti60 side weld zone (WZ), Ti\u003csub\u003e2\u003c/sub\u003eAlNb side WZ, Ti\u003csub\u003e2\u003c/sub\u003eAlNb side TMAZ, Ti\u003csub\u003e2\u003c/sub\u003eAlNb side heat affected zone (Ti\u003csub\u003e2\u003c/sub\u003eAlNb HAZ), and Ti\u003csub\u003e2\u003c/sub\u003eAlNb side BM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe width of Ti60 side TMAZ together with itse WZ is approximately 1000 \u0026micro;m. Compared with the Ti60 side BM, grains at the Ti60 side TMAZ are severely deformed and elongated along the oscillating interface. The microstructure of the Ti60 side WZ is dense and uniform, while the Ti60 BM cannot be identified. The width of the WZ together with the TMAZ on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side is approximately 1500 \u0026micro;m, larger than that on the Ti60 side joint. There is developed a wide HAZ between Ti\u003csub\u003e2\u003c/sub\u003eAlNb side TMAZ and the BM. This can be attributed to that large B2 grains(as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) of Ti\u003csub\u003e2\u003c/sub\u003eAlNb exhibits good thermal strength, with small plastic deformation and weak plastic flow during welding, resulting in less heat being carried away by the flash. The heat conduction influence range on Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint is larger, ultimately developing a wider HAZ between the TMAZ and BM on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint. The heat-affected zone is affected by heat conducted away and to lesser extent by the stress state, with large B2 grains showing minimal deformation similar as BM.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Microstructure evolution in different zones of joint\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the SEM microstructure in each zone of the joint. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows that of Ti60 BM, which consists of a large number of equiaxed α, with β phases distributed at α boundaries. The size of the α phase grains is greater than 20 \u0026micro;m. There are few titanium silicides scattered at the α grain boundaries, which can pin grain boundaries and improve thermal stability of Ti60 [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the SEM microstructure of the Ti60 side TMAZ, where α grains are elongated and deformed. The white β at the α grain boundaries retains its original state, but silicides at the α grain boundaries have disappeared. This is related to welding, where material is affected by the combined effects of high temperatures and large shear forces, which deform equiaxed α grains, while silicides at grain boundaries decompose due to heat. However, since equiaxed α still remains, it can be deduced that temperature at the Ti60 side TMAZ does not exceed the β-transus temperature (of 1050\u0026deg;C [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee shows the SEM microstructure of the Ti60 side WZ, which consists of undeformed fine grains smaller than those of BM, and the silicide in the Ti60 BM having disappear. The average grain size of WZ is 5.7 \u0026micro;m, which is significantly finer than that in the base material, as dynamic recrystallization took place during welding. In the published study [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] it was shown that during LFW of titanium alloys temperatures exceed 1200\u0026deg;C, and the complete α \u0026rarr; β transformation will occurs in WZ, forming uniform high-temperature β phase. At the same time, due to thermal-mechanical coupling, temperatures exceeded 1200\u0026deg;C as dynamic recrystallization occurred in this area due to increased cooling rates, the αˊ martensite is precipitating from the β phase, since Ti60 is a near-α titanium alloy with β-stabilizing elements [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] .\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb shows the SEM microstructure of Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM, where the B2 grain size is larger than that of the α grains in the Ti60 BM, with numerous needle O phase grains inside B2 grains and at grain boundaries. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed shows the SEM microstructure of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb HAZ, with a few needle O phase grains inside the B2 grains in HAZ decomposing and dissolving into the B2 matrix. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef shows the SEM microstructure of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb TMAZ, with significant degree of O phase dissolution. In addition, due to the large grain size of Ti\u003csub\u003e2\u003c/sub\u003eAlNb, it is difficult to study TMAZ grains with high-magnification SEM. So, EBSD characterization was used for the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side TMAZ, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The low-magnification inverse phase figure (IPF) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea) shows the B2 grains to be elongated and deformed due to high temperatures and stresses developed during welding. From the high-magnification IPF image (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), it can be seen that dynamic recrystallization of B2 grains occurred in the TMAZ near the WZ, producing randomly oriented recrystallized B2 grains of smaller size than those in the BM. The SEM microstructure of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb WZ is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg, where there exists single B2 phase, and the needle O phase grains of BM have dissolved completely. The WZ consists of equiaxed B2 grains that are much smaller than those in the BM, with a size of 5\u0026ndash;10 microns, as complete B2 dynamic recrystallization did occur, which suggests that the interface temperature exceeded the transformation temperature of O of titanium alloys[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. As the temperature increases during welding, the O phase on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side WZ quickly and completely transforms into high-temperature B2 phase. At the same time, under high strain rate deformation in the WZ, dynamic recrystallization of B2 phase take places, to form equiaxed B2 grains of smaller size than those in the BM. When welding is stopped, the cooling rate reaches up to 300 k/s [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], which exceeds the critical cooling rate for B2\u0026rarr;O transformation to occur. So, the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side WZ is uniformly composed of B2 phase grains.\u003c/p\u003e \u003cp\u003eIn this study, dynamic recrystallization took place on both sides of the WZs. The recrystallization distribution of WZ on both sides of the joint was investigated, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The WZ on the Ti60 side contains a larger number of blue recrystallized grains together with a large number of yellow subgrains (see Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea); similarly, the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side WZ also contains a large number of subgrains. So, it can be deduced that the recrystallization processes of WZ on both sides of the joint is accompanied with subgrains. Previous published research [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] has shown that in the case of high stacking fault energy Ti-based alloys, subgrains form during recrystallization, which is typical of continuous dynamic recrystallization.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 Interface microstructure and bonding mechanism\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea shows the SEM microstructure of the interface, where the Ti60 side consists of dense acicular structures, and there are no recrystallization grain boundaries. The temperature on the Ti60 side exceeded the β-transus temperature (of 1050\u0026deg;C [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]), which produces high-temperature β grains and produces fine recrystallized grains by dynamic recrystallization. It was followed by dense henlized grais which formed inside recrystallized grains during the quick cooling stage once welding finished. Due to the high content of β elements at the interface in Ti\u003csub\u003e2\u003c/sub\u003eAlNb, the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side interface consisted of a uniform B2 phase in the joint, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. It can also be clearly observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea that the αˊon Ti60 side of interface grows into the B2 phase on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side interface. The low-magnification bright-field image of the interface is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb. The left side of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb is Ti60, where numerous tiny acicular αˊ can be seen; while the right side where Ti\u003csub\u003e2\u003c/sub\u003eAlNb is placed, there are B2 recrystallized grains. The blue framed detail in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb included the B2 recrystallized grain, and it is enlarged in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec. The grain was analyzed using selected area electron diffraction (SAED) and compared to standard patterns [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], which showed that the B2 grain has a body-centered cubic [001] pattern, as the crystal zone axes are parallel to the [001] direction, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee shows the high-angle annular dark field (HAADF) image of the interface, and the EDS line scan is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef. The latter shows that Ti diffuses from the Ti60 side to the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side at the interface, while Al and Nb from the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side diffuse toward the Ti60 side. The width of the diffusion layer is 1.54 \u0026micro;m. Previous studies investigating the forming mechanism of such cases [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] have shown that high pressure and large deformations can eliminate crystal lattice defects at the join interface, allowing for mutual diffusion of interfacial elements. It enhances the interatomic bonding force and increases the joint strength. Although LFW has a bery short duration, there exist similarities with diffusion welding at high pressure and large deformations. In addition, lattice distortions, dislocations, and vacancies produced by intense plastic deformation reduce the activation energy necessary for diffusion. This lets interface elements to diffuse in a short time, which eliminates the original Ti\u003csub\u003e2\u003c/sub\u003eAlNb/Ti60 interface and develops of a new joined interface.\u003c/p\u003e \u003cp\u003eFrom the SEM and TEM observations, the bond process at the Ti\u003csub\u003e2\u003c/sub\u003eAlNb/Ti60 interface during LFW can be summarized as follows: during welding the interface evolves into a phase boundary between the β and B2 phases at high temperatures. The β and B2 phases have identical crystal structures (both body-centered cubic structure), but their elemental compositions are of their parent materials. Under the combined effect of high temperature and large stresses during LFW, alloy elements in the high-temperature β phase on the Ti60 side and the high-temperature B2 phase on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side diffuse mutually. The original interface disappears, and an element transition layer of 1.54 \u0026micro;m thickness is formed between the two phases. After quick cooling, acicular αˊ martensite precipitates on the Ti60 side interface, while Ti\u003csub\u003e2\u003c/sub\u003eAlNb had no precipitated phase and retained the B2 phase. The αˊ on the Ti60 side interface grows into B2 grains on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side. This process is responsible for metallurgical bond of the joint.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Mechanical properties of joints\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Tensile strength\u003c/h2\u003e \u003cp\u003eThe tensile strength test results of joint are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The yield and ultimate tensile strength of the joint were 878 MPa and 920 MPa, respectively, which are equivalent to those of the Ti60 BM. The elongation of the joint was 1.7%, due to limited plasticity of the joint. After the tensile strength measurement, the specimens are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, where the location of fracture is close to the interface, with no obvious neck formed, confirming further the limited plasticity of the joint. A metallographic specimen from the fracture location was prepared and studied with OM, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. Fracture was located at approximately 1500 \u0026micro;m away from the interface on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side of the joint, at the boundary of TMAZ and HAZ. Analysis shows that the strengthening phase O grains in the TMAZ and HAZ of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint have dissolved, which allows for failure due to localized plastic strain concentration during tensile loading [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. But, complete dynamic recrystallization takes place in WZ, and forms a large number of recrystallized B2 grains which are significantly smaller than those in the BM, which has a strengthening effect. At the Ti60 side joint, whose BM grain size is smaller than that of Ti\u003csub\u003e2\u003c/sub\u003eAlNb\u0026rsquo;s BM, there is no α strengthening phase dissolution during welding, and the mechanical strength of this side joint is higher than that of the TMAZ and HAZ of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint. In addition, the interface bond strength was higher than that of the HAZ and TMAZ of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint, as even though the Ti60 and Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloys had differences in composition and structure, there developed sound interface metallurgical bond. Plastic deformation during tensile testing was primarily in the TMAZ and HAZ of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint, elongation of the joint is lower than that of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM, at 1.7%.\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\u003eTensile strength measurements\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=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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\" colname=\"c1\"\u003e \u003cp\u003eSpecimen\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYield strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTensile strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eElongation (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJoint\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e878\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e920\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi60 BM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e876\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e941\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e13.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi\u003csub\u003e2\u003c/sub\u003eAlNb BM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.6\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\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to investigate further fracture, fracture surface was studied using SEM, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The fracture surface is uneven (see Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea), with no obvious shear lip, and shows brittle fracture characteristics. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb is an detailed view of area A in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea, where there are river-like patterns. In the further detailed view of Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec, cleavage steps and shallow dimples can be seen. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ed is a detailed view of area B, where it can be seen that a large number of ductile dimples. Overall, the fracture surface of the joint exhibits quasi-cleavage fracture characteristics [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3 Impact strength\u003c/h2\u003e \u003cp\u003eThe impact strength measurement results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The impact toughness of the Ti60 BM (15.1 J/cm\u0026sup2;) is higher than that of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM (6.6 J/cm\u0026sup2;), and the impact toughness of the joint (13.0 J/cm\u0026sup2;) is also higher than that of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the impact strength specimens following the measurement, where all specimens broke at the notch, and fracture paths were terminology, as the interface has high impact toughness.\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\u003eImpact toughness of joint\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecimen\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eImpact toughness (J/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJoint\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi60 BM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e15.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi\u003csub\u003e2\u003c/sub\u003eAlNb BM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.6\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\u003e \u003c/p\u003e \u003cp\u003eThe fracture surface of the specimen is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb shows a detailed view of fracture surface of the red frame in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea, where the fracture surface is smooth. The notch is at the bottom edge of the fracture surface in this figure, with crack initiating from the notch center. The fracture surface contains numerous dimples (see Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb), which confirms experimental result where impact toughness of joint interface is high. The XRD measurement was taken at the impact fracture surface (see Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e), which identified TiAl\u003csub\u003e3\u003c/sub\u003e and NbAl\u003csub\u003e3\u003c/sub\u003e intermetallic compounds. As was shown in Section \u003cspan refid=\"Sec10\" class=\"InternalRef\"\u003e3.1.3\u003c/span\u003e, the metallurgical bond of the joint interface is achieved through mutual diffusion of metals during welding, which develops a 1.54 \u0026micro;m transition layer. The XRD analysis of fractured interface showed limited TiAl\u003csub\u003e3\u003c/sub\u003e and NbAl\u003csub\u003e3\u003c/sub\u003e intermetallic compounds, which are the reason that the interface impact toughness is not lower than that of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe following conclusions can be made:\u003c/p\u003e \u003cp\u003e(1) Continuous dynamic recrystallization occurs on both sides of the joint interface, forming fine equiaxed grains with smaller size than those of the BMs. Under the combined effects of high temperatures and large shear forces during welding, the microstructure of Ti60 TMAZ is elongated. On the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side TMAZ, the large B2 grains become also elongated, and B2 dynamic recrystallization occurs in the TMAZ near the WZ. In addition, the O phases within the B2 grains are dissolved in this zone; the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side HAZ is mainly effected by heat during welding, so B2 grains are not deformed. The O phases within the B2 grains in HAZ undergo limited decomposition, as the temperature at the HAZ is lower than that of the TMAZ.\u003c/p\u003e \u003cp\u003e(2) The interface undergoes a transformation from the original friction interface \u0026rarr; the β/B2 phase interface at quasi-steady friction stage \u0026rarr; the αˊ/B2 phase interface after quick cooling at the end of welding, with acicular αˊ on the Ti60 side interface growing into B2 martix on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side interface, which removes the initial interface. In addition, the combined effect of high temperatures and stresses together with large deformations during welding, there is adequate diffusion of Ti, Al, and Nb on both sides of the interface. This develops a diffusion layer of 1.54 microns thickness with the intersolute elements, which is the main mechanism for the interface metallurgical bond.\u003c/p\u003e \u003cp\u003e(3) The tensile strength of joint is 920 MPa, which is 97.9% of the Ti60 BM, with elongation of 1.7%. The failure zone of the joint is located at the interface between the TMAZ and HAZ on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side joint. This is because the strengthening O phases dissolve extensively in this zone, with no dynamic recrystallization occuring to allow for fine grain strengthening effect. The impact strength energy of the joint interface is 13.0 J/cm\u0026sup2;, higher than that of the Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM, as the interface shows improved toughness compared to the Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM. This is associated to the formation of intermetallic compounds including TiAl\u003csub\u003e3\u003c/sub\u003e and NbAl\u003csub\u003e3\u003c/sub\u003e at the interface diffusion layer.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDeclaration of competing interest\u003c/h2\u003e \u003cp\u003eThe authors declare that there are no competing financial interests or personal relationships that could influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFundings\u003c/h2\u003e \u003cp\u003eThis work was supported by the National Natural Science Foundation of China (grant no. 52105400) and Heilongjiang Advanced Friction Welding Technology and Equipment Key Laboratory (grant no. 2025001)..\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eJiaying Li: Investigation, Methodology, Writing original draft. Tiejun Ma: Methodology, Writing\u0026ndash;review \u0026amp; editing Resources. Hongbo Zhang: Formal analysis. Xiawei Yang: Investigation. Wenya Li: Formal analysis. Achilles Vairis: Formal analysis, Writing\u0026ndash;review.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was supported by the National Natural Science Foundation of China (grant no. 52105400) and Heilongjiang Advanced Friction Welding Technology and Equipment Key Laboratory (grant no. 2025001)..\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eThe processed data required to reproduce these findings cannot be shared at this time as data are part of a larger ongoing study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLi SQ, Mao Y, Znang JW et al (2002) Effect of microstructure on tensile properties and fracture behavior of intermetallic Ti\u003csub\u003e2\u003c/sub\u003eAlNb alloys. 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Mater Lett 304:130597\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTang B, Qi XS, Kou HC et al (2016) Recrystallization Behavior at Diffusion Bonding Interface of High Nb Containing TiAl Alloy. Adv Eng Mater 18(4):657\u0026ndash;664\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"linear friction welding, Ti2AlNb, Ti60, dissimilar joint, interface microstructure, tensile strength, impact strength","lastPublishedDoi":"10.21203/rs.3.rs-8204363/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8204363/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, microstructure evolution and the interface metallurgical bond of linear friction welded dissimilar Ti\u003csub\u003e2\u003c/sub\u003eAlNb/Ti60 joint were studied. The relationship of microstructure to tensile and impact strength of the joint were analyzed. Results show that continuous dynamic recrystallization occurred on two weld zones (WZ) during welding, forming equiaxed fine grains which were smaller than those of the two base metals. On the Ti60 side thermo-mechanically affected zone, α grains were elongated under the high temperature and shear force effects; while on the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side, the large B2 grains were also elongated where a large number of O phases were dissolved. In the Ti\u003csub\u003e2\u003c/sub\u003eAlNb side heat affected zone, the B2 grains were not deformed, and the O phases inside B2 grains were decomposed, as the welding temperature was lower than that in the TMAZ. The interface metallurgical bond was achieved through mutual diffusion of Ti, Al and Nb, producing an element transition layer of 1.54 \u0026micro;m composed of TiAl\u003csub\u003e3\u003c/sub\u003e and NbAl\u003csub\u003e3\u003c/sub\u003e intermetallic compounds. The tensile strength of the joint was 920 MPa, which is 97.9% of the Ti60 BM, but elongation was 1.7%. Failure of joint during tensile strength testing was located at the junction of Ti\u003csub\u003e2\u003c/sub\u003eAlNb side TMAZ and HAZ, where the O phases dissolve and there was no dynamic recrystallization of the B2 grains. So, the plastic deformation of the joint when a tensile load was applied was concentrated there, producing limited elongation. The impact energy at interface was measured to be 13.0 J/cm\u0026sup2;, which is higher than that of Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM, as the toughness of the interface is better than that of Ti\u003csub\u003e2\u003c/sub\u003eAlNb BM, which is related to TiAl\u003csub\u003e3\u003c/sub\u003e and NbAl\u003csub\u003e3\u003c/sub\u003e intermetallic compounds forming at the interface element transition layer.\u003c/p\u003e","manuscriptTitle":"Insights into Microstructure Evolution and Mechanical Properties of Linear friction welding of Dissimilar Ti2AlNb and Ti60 Alloys","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-22 16:26:46","doi":"10.21203/rs.3.rs-8204363/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-12-20T05:39:39+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-19T09:55:34+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Welding in the World","date":"2025-12-04T05:34:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-30T22:22:24+00:00","index":"","fulltext":""},{"type":"submitted","content":"Welding in the World","date":"2025-11-28T02:55:07+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0da8f111-be65-47ec-b1de-33ce163ec4d6","owner":[],"postedDate":"December 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-10T06:46:14+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-22 16:26:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8204363","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8204363","identity":"rs-8204363","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}