Influence of post-treatment on the performance of SLM forming 18ni300 electroplated coatings

Influence of post-treatment on the performance of SLM forming 18ni300 electroplated coatings | 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 Influence of post-treatment on the performance of SLM forming 18ni300 electroplated coatings Wei Xu, Xiangli Liu, Yong Li, Guoyang Zhao, Gaojian You This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6815548/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Hot isostatic pressing (HIP) is widely used to enhance the intrinsic properties of additively manufactured 18Ni300 martensitic aging steel, which can eliminate internal defects and optimize the microstructure of additively manufactured metals. However, there is still a lack of systematic knowledge about the influence of hot isostatic pressing on the interfacial properties of chromium plating on its surface, which makes it difficult to provide a reliable theoretical basis and process guidance for the precise optimization of plating properties under complex working conditions. In order to solve the above needs and technical problems, this paper centers on the post-treatment strengthening effect of chromium plating on the surface of additively manufactured 18Ni300 alloy to carry out in-depth investigation. Without post-treatment of pure chromium plating layer flatness and roughness degradation phenomenon obviously exists, through the XRD analysis to confirm that the composition of its physical phase contains Fe-Ni phase, FeNiCr phase and monolithic Cr residual phase. The microstructure response of chromium plating layer after heat treatment shows complex characteristics, transverse crack network and delamination phenomenon is triggered by the internal stress relaxation and crystal structure reconstruction of the plating layer. 600℃/70MPa hot isostatic pressing conditions, the plating layer surface flatness and interfacial straightness can be maintained, but there are still many internal pores, and densification needs to be improved. 1150℃/150MPa hot isostatic pressing process has a significant effect on the optimization of the performance of the layer: the surface flatness and interface straightening can be maintained, and the internal porosity still has more holes, and densification should be improved. The optimization effect is obvious: the surface flatness is well maintained; the interface with the substrate is formed; the hardness is greatly increased to 406.3-673.1HV0.2 ± 10%, and the monolithic phase disappears completely. The effective modulation of the atomic diffusion behavior at the plating-substrate interface by the hot isostatic pressing treatment was confirmed by the study: metallurgical bonding was strengthened; crack formation was suppressed; and the hardness and corrosion resistance were significantly improved. The results of the study open up an important new technological path for the optimization of surface protective layers of additively manufactured alloys. Physical sciences/Physics/Condensed matter physics Physical sciences/Materials science Additive manufacturing Post-treatment of electroplating Hot isostatic pressing 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 As a star material in the field of additive manufacturing, martensitic ageing steels show excellent application potential in Selective Laser Melting (SLM) technology with their unique alloy system. The advantages of high strength, high toughness and excellent process performance make it the material of choice for missile shells, pressure vessels, cold-drawn molds, etc. It occupies an irreplaceable position in the manufacturing of aerospace key load-bearing components, the processing of precision mold cavities, and the manufacturing of high-end equipment under extreme conditions [ 1 – 4 ]. 18Ni300 martensitic aging steel is a new type of steel made by adding Co, Al, M, M and P to the Fe-18Ni alloy. 18Ni300 martensitic steel is formed by adding Co, Al, Mo, Ti and other elements on the basis of Fe-18Ni alloy, and then undergoes aging treatment after solid solution treatment. intermetallic compounds, such as Ni 3 Mo, Fe 2 Mo, Ni 3 Ti and so on, precipitate and precipitate in martensitic region. The material has excellent strength performance and equally outstanding plasticity and toughness, with a yield strength of between 1400–2400 MPa. Conventional manufacturing methods for producing complex 18Ni300 parts suffer from long production cycles, high costs and insufficient machining accuracy, which limits the wide application of this alloy in many fields [ 5 – 9 ]. Selected-area laser melting technology is a new rapid prototyping technical method. Computer-aided design at the same time through the laser beam irradiation metal powder melting, layer by layer printing and layer by layer accumulation to achieve the rapid manufacturing of complex parts. The complex structure of the molded parts is not limited, and the ultra-fast cooling rate ensures the superiority of accuracy and performance, while the production cycle is short and low cost [ 10 – 14 ]. There have been a number of reported examples of domestic and international research on SLM forming of martensitic aged steels.Riccardo Casati et al [ 15 ] used laser selective zone melting technology to realize the forming process of 18Ni300 material, and the aging treatment process was applied to the formed specimens. The team's data show that the evolution of the internal organization of the material accompanies the aging process and the precipitation of reinforcing phases, which leads to a significant increase in the strength properties of the alloy, while the plasticity indexes show a decrease. The mechanical properties obtained after aging treatment are comparable to those of conventional forged parts.Kempen K et al [ 16 ] focused on the scanning speed and powder thickness of the two key variables, systematically studied the 18Ni300 material microstructure characteristics and mechanical properties of the mechanism of influence, that: too high a scanning speed or too large a thickness of the powder will lead to the deterioration of the material densification index. The laser selective zone melting technology, which is in the stage of continuous optimization, is still facing many challenges. Extreme thermal gradient conditions and transient solidification characteristics are inherent in this process, and the formation of surface defect networks is inevitable during the cumulative build-up process of 18Ni300 alloy layer by layer. The complex coupling of thermodynamic and kinetic factors dominates the melting-solidification process, which is particularly prominent, and process problems such as the tendency of powder spheroidization occur frequently. The combined effect of the above factors significantly increases the difficulty of controlling the forming process, and the negative impact of the generation of pore-type defects on the surface properties has been confirmed by a number of studies [ 17 ]. At the current stage, the research work on SLM forming 18Ni300 martensitic aging steel is mainly focused on the optimization of forming process parameters and post-treatment technology and other directional exploration. It is worth noting that there is relatively little research in the field of surface modification of SLM forming 18Ni300. Maraging steel surface modification coating preparation method exists a variety of methods, including arc spraying technology, laser cladding process, electroplating treatment and chemical plating and other traditional means. The plating obtained by these methods has a significant effect on the protective function of the base material. As a time-honored surface treatment technology, the electroplating process is particularly suitable for surface enhancement of ultra-high-strength steel materials. The wear and corrosion resistance of the chromium plated substrate surfaces were significantly improved [ 18 – 23 ].Sundar et al. [ 24 ] showed a significant increase in the fatigue life of 15-5PH ultra-high-strength stainless steel samples pretreated with laser shot peening followed by hard chromium plating compared to the unshot-peened control group. The fatigue cracks sprouted at the microcracks in the plating region, but the direction deflection phenomenon occurred during the expansion to the matrix region, and it is believed that this method can effectively inhibit the continuous expansion of fatigue cracks.Liao et al [ 25 ] showed that when different concentrations of nano-silicon nitride particles were doped into the chromium plating solution for electrodeposition under DC conditions, the prepared Cr-C/Si3N4 composite plating layer had special properties. The volume fraction of Si3N4 particles in the plating layer showed a regular change of first increasing and then decreasing with the variability increase of Si3N4 concentration in the plating bath. Samples obtained under specific process parameters showed that the Si3N4 particles could be uniformly dispersed in the distribution of the Cr-C matrix.Bellemare et al [ 26 ] conducted a systematic study on the relationship between the densities of chromium plated layers on the surface of AISI4340 steel and hydrogen embrittlement phenomenon. Through the preparation of different current density conditions and whether or not sandblasted specimen group comparison analysis found that: the key factors leading to the occurrence of hydrogen embrittlement phenomenon of 4340 steel is the plating density of the differential performance. Although the chromium plating treatment can significantly improve the wear resistance of the steel surface, the degradation of the matrix fatigue performance is unavoidable. Typically, large residual stresses are generated during the plating process, microcracks are formed inside the chromium plating layer, material properties on both sides of the crack interface are differentiated, deflection and bifurcation phenomena are easy to occur, and the stress intensity factor is reduced at the tip of the crack. When the crack density in the plating layer reaches a high level, the spalling phenomenon is very easy to appear in the actual use process. The development and regulation of new protective technologies such as nano-strengthening and composite plating have been developed through the chromium plating process for many years [ 18 , 27 – 30 ]. There are relatively few studies on the post-processing of electrochromium plating coatings on steel surfaces, especially for electrochromium plating on SLM-formed 18Ni300 surfaces. Isotropic pressure can be applied by the hot isostatic pressing (HIP) technique, and material pressing and sintering is accomplished under the synergistic effect of temperature and pressure. Optimization of the material organization, elimination of internal defects in the parts and improvement of mechanical properties can be achieved by this technique [ 31 – 33 ]. The internal pore diffusion model of high-temperature alloys was investigated by Epishin et al [ 34 ], and the void diffusion occurs at high temperatures and pressures, and the pore defects are effectively repaired.Plessis et al [ 35 ] concluded that the SLM molded parts are of excellent quality and very high densities after hot isostatic pressing, and the reduction of surface porosity of the molded parts can be achieved by increasing the pressures and prolonging the holding time. Hot isostatic pressing technology is commonly used in the field of integral forming of complex components and casting densification process, by virtue of the dual action of high temperature and high pressure, internal porosity, shrinkage and segregation defects can be effectively eliminated. For SLM18Ni300 electroplated coatings to carry out hot isostatic pressing post-treatment research work is still in a state of blank. In this paper, a combination of multi-scale experimental means and characterization methods are used to post-treat the SLM18Ni300 electroplated layer in a hot isostatic pressing device. The heat-treated plated layer is used as a control sample to systematically observe the changes in microstructure. The structural composition and performance parameters were also comprehensively tested, thus revealing the influence of hot isostatic pressing technology on the organizational structure and performance characteristics of SLM18Ni300 electroplated coatings. The goal of intelligent regulation and integration of the post-treatment process is expected to be realized through this research, and this breakthrough is expected to promote the technological innovation in the field of high-end manufacturing, and provide a more universal solution for the surface technology in the field of additive manufacturing of high-performance metal materials. 2. Materials, Equipment and methods 2.1 Test Equipment and Materials This test adopts the DMP Flex350 selective laser melting and forming equipment manufactured by GF, which is equipped with a soft scraper powder feeding system to realize uniform powder laying and efficient recycling, and provide hardware guarantee for high-precision forming. The core component is a 500W fiber laser with a spot diameter of 100µm, capable of delivering stable laser energy. Combined with an adjustable powder thickness of 10–100µm and a scanning speed of up to 7m/s, the dynamic behavior of the molten pool can be precisely adjusted to meet different molding requirements. The built-in atmosphere control system ensures that the volume fraction of oxygen in the processing environment is always ≤ 0.0025%, which effectively avoids oxidative contamination of metal powder at high temperature and guarantees the purity of the molded parts. 275mm×275mm substrate size provides sufficient space for diversified specimen preparation and supports high-quality molding of complex geometrical structures. The raw material for the test is 18Ni300 maraging steel powder prepared by vacuum aerosol method, which gives the powder excellent sphericity and smooth surface morphology, and significantly improves the fluidity and stacking density of the powder in the process of powder spreading. The particle size distribution of the powder is concentrated in the range of 25 ~ 53µm, the Hall flow rate is 13.80s/50g, and the bulk density reaches 4.18g/cm³, which all meet the strict requirements of the SLM process for the powder fluidity and filling efficiency. Its chemical composition is shown in Table 1 , and the precise proportion of each alloying element lays the foundation for the mechanical properties of the subsequent molded parts. Table 1 Chemical compositions of 18Ni300( mass fraction, %) Ni Mo Co Cr Al C Fe 17.70 4.79 9.05 0.31 0.07 0.007 Margin 2.2 Test Scheme The test adopts SLM forming process, the 18Ni300 alloy powder is uniformly preset in the forming chamber of the DMP Flex350 equipment, and the printing program is initiated after the evacuation-argon replacement cycle (high-purity argon purity ≥ 99.999%) to construct an oxygen-free environment. Set forming process parameters are as follows: laser power 230W, scanning speed 1100mm/s, scanning spacing 0.1mm, pavement layer thickness of 30µm, in the 275mm × 275mm substrate prepared on the specifications of 15mm × 15mm × 17mm cubic substrate. After the forming was completed, the specimen was separated from the substrate by precise wire cutting, and the surface was sequentially polished and mechanically polished to a mirror state, and then placed in an ultrasonic cleaner with an ethanol solution for 20 min, and then treated with anodic electrode degreasing, deionized water rinsing, and activation, to provide a clean and active surface for chromium electroplating. The plating process adopts constant voltage mode, controlling voltage 4V, current 10A, and the pretreated substrate is immersed into the chromium plating electrolyte and deposited for 5min, and then rinsed with deionized water and dried in the oven at 100℃ for 30min immediately after the end of the process, to obtain the chromium plating intermediate specimen. Subsequently, it was divided into two groups for post-treatment: one group was placed in a hot isostatic press, argon gas was introduced at high temperature and constant pressure was applied, and after holding for 3 hours, it was slowly cooled to room temperature with the furnace to form a hot isostatic strengthening of the plating layer; the other group, as a control, was put into a box-type heat treatment furnace, and after holding for 3 hours at 900°C, it was air-cooled to obtain the conventional heat treatment of plated specimens, and the box-type heat treatment furnace is shown in Fig. 1 (b). The main process parameters of the test are shown in Table 2 . JSM-IT500 scanning electron microscope equipped with EDS spectrometer is used to observe the microscopic morphology of the interface between the plating layer and the substrate, and the equipment diagram is shown in Fig. 1 (a), and the distribution pattern of Cr, Fe and other elements in the interface area is analyzed by line scanning technology; HV-1000A microhardness tester is used to test the hardness of the area near the interface, and the load is set to be 0.2kg and the holding time to be 10s, and the arithmetic mean value is taken to ensure the reliability of the data after eliminating the extreme values. Set the load 0.2kg, holding time 10s, each specimen selected 10 effective measurement points, remove the extreme value to take the arithmetic average to ensure the reliability of the data. The whole test program provides a rigorous experimental basis for revealing the strengthening mechanism of hot isostatic pressing on the chrome-plated layer on the surface of SLM forming 18Ni300 by precisely controlling the process parameters and characterization methods. Table 2 Main process parameters of post-treatment after the experiment Sample No. Heat treatment process Post-treatment after hot isostatic pressing Temperature /℃ Time /H Temperature /℃ Pressure /MPa Time /H 1 / / / / / 2 900 3 / / / 3 / / 600 70 3 4 / / 1150 150 3 3. Test Results and Discussion 3.1 Microstructure of the coating Using laser selective zone melting (SLM) technology to form 18Ni300 martensitic aging steel is obviously different from the traditional forging or casting alloys of uniform equiaxial crystalline organization, and its microstructure shows a typical fish scale melt channel structure (Fig. 2 ). High-energy laser beam on the powder layer point-by-point melting and rapid solidification process, the higher single-pass molten pool cooling rate formed a dynamic non-equilibrium solidification interface characteristics. The fine columnar crystals extending directionally along the heat dissipation gradient of the melt pool were mainly distributed in the center region of the melt channel (Fig. 2 (a)), and the growth direction was approximately perpendicular to the axis of the melt channel. This reflects that the substrate normal direction is the dominant heat flow direction during laser scanning. The complexity of the heat dissipation path and the higher cooling rate of the cellular crystals distributed in the edge region of the channel in direct contact with the unmelted powder lead to an increase in the degree of subcooling. Rapid nucleation and lateral growth of cytosolic nuclei form a uniform and dense microstructure in this region. The complexity of the thermal history of the SLM layer-by-layer process is revealed by the coexistence of multiple oriented columnar crystals inside the channel shown in Fig. 2 (b). During subsequent channel scanning, the solidified layer undergoes secondary remelting and localized heating. Partial dissolution of the previously formed columnar crystal boundaries occurs, and a deflection of the heat flow direction in the newly solidified region due to the overlapping melt pool results. The formation of the multi-directionally grown columnar crystal structure is finally completed. The junction region in Fig. 2 (d) shows the coexistence of cytosolic and irregular columnar crystals, which is essentially a product of the solidification interface destabilization, and this property is confirmed. In the high cooling rate region at the edge of the channel, the initial formation of cytosolic crystals due to solute enrichment triggers the competitive growth of dendritic arms, which is clearly visible. The subsequent thermal activation of the melt pool captures the transformation of some of the cytosolic crystals by the rapid extension of secondary dendrite arms in the dominant direction. After the elongated columnar crystal transformation is completed, the formation of a polymorphic mixed solidification organization is finally achieved. The significant presence of melt channel size variability shown in Fig. 2 c is closely related to the interlayer thermal coupling effect unique to selective laser melting technology. Subjected to laser radiation, the lower layer of solidified tissue is reheated above the austenitization temperature when melting of the upper powder layer occurs. A pinned melt channel with a wide upper and narrower lower layer is formed, which gradually decreases the melt pool depth as the number of accumulated layers increases [ 35 – 37 ]. The laser body energy density has a direct effect on the melt pool behavior, and the laser body energy density can be calculated from Eq. 1 : $$\:E=\frac{P}{s\times\:v\times\:t}$$ 1 Where E is the laser body energy density (J/mm 3 ), P is the laser power (W), t is the thickness of the powder laying layer (mm), s is the scanning spacing (mm), and v is the scanning speed (mm/s). The laser power and scanning speed are critical for the control of the magnitude of the energy density of the laser body [ 38 – 40 ]. Insufficient energy to completely melt the powder particles occurs when the laser power is too low or the scanning speed is too fast. The grain boundaries are enriched with unfused defects, including powder residues and half-molten particles. Metal evaporation and spattering phenomena occur at too high a power or too slow a speed, forming porosity defects or spheroidization defects upon cooling [ 41 , 42 ]. It can be seen that the elimination of the surface defect network is difficult to be realized by simply adjusting the energy density. The surface integrity is thereby reduced by the combined effect of micropores formed during solidification, residual stresses, and unfused interfaces. The necessity of surface modification treatments for 18Ni300 materials is particularly evident in the SLM molding process. As shown in Fig. 3 , the microstructure of the pure chromium plating layer presented on the surface of the SLM formed 18Ni300 substrate shows a significant deterioration in both flatness and roughness characteristics. The multidimensional mechanism of the plating layer formation process can be explored in depth. The Cr ion concentration and additive concentration are generally recognized as the most important regulatory parameters that decisively influence the key factors of plating layer quality. The control effect of these parameters, in turn, plays a significant role in governing the flow mass transfer process. In the unstirred plating system, the absence of a forced convection environment makes the transport of Cr ions and additives to the microscopic defective regions dependent only on their own concentration gradients. As the plating time increases and the reactants continue to be consumed, the problem of insufficient material transport becomes apparent. The formation of microcracks is thus induced. The nucleation-growth model can be used as a theoretical basis to explain the electroplating process, as shown in Eq. 2: $$\:\omega\:=Bexp（-\frac{T}{{\eta\:}^{2}}）$$ where T is the plating temperature, B is the constant parameter of the copper substrate, ω is the nucleation rate, and η is the cathodic polarization potential [ 43 ]. When the current condition of 10 mA was set, the cathodic polarization potential showed a decreasing trend, which triggered the phenomenon of decreasing nucleation rate. The initial growth state of the plated layer is significantly affected. The essential process of electrodeposition of chromium involves the gradual deposition of dichromate ions to metallic chromium in the presence of a DC electric field. Four key links constitute the process: diffusion to the electrode surface occurs firstly with dichromate ions; subsequent migration to the interior of the bilayer driven by the electric field, a colloidal film of chromium alkali chromate is formed at the electrode interface; sulfate ions act as a catalyst to promote the dissolution of this colloidal film, which acquires electrons to be converted into adsorbed chromium atoms to realize chromium ions [ 44 – 46 ]. Under the condition of flat substrate surface, the full discharge mode dominates, and the synchronized nucleation phenomenon appears on the steel substrate surface. When obvious concave and convex structures exist on the substrate surface, the raised parts become the concentration area of the discharge, and the partial discharge mode is revealed. The limited number of raised areas and their small size lead to the establishment of a specific correlation between roughness and chromium grain characteristics: a tendency towards finer chromium grain sizes and sparser stacking patterns are observed with increasing roughness. The microstructure evolution of the electrochromium plating layer formed on the surface of SLM18Ni300 substrate after heat treatment presents complex characteristics. The phenomena of transverse crack networking and delamination are shown in Fig. 4 , which can be essentially attributed to the synergistic effect of stress relaxation process and crystal structure reconstruction within the plated layer. During the heat treatment process, the chromium plating layer undergoes three critical transformation stages: martensitic decomposition occurs in the 300–400 temperature range, leading to volume shrinkage, phase transition stresses superimposed on the quenching residual stresses accumulated during the plating process, and a three-dimensional stress field is thus formed inside the plating layer. 600°C temperature threshold is exceeded, and brittle Fe-Cr intermetallic compound layer is formed at the plating-substrate interface, which has lower shear strength than the substrate material. Its shear strength is much lower than that of the base material, and the dominant channel for crack extension is thus established. The distribution of the thermal stress gradient shows an enhanced trend, and the difference in the coefficients of thermal expansion between the plating and the substrate leads to the phenomenon of interfacial exfoliation during the cooling process. The crack extension path changes from through-crystal mode to along-crystal mode, and the hard and brittle characteristics are strengthened so that the cracks penetrate through the plating layer and invade the matrix, and the typical morphology of “plating-substrate hybrid fatigue source” is thus formed [ 47 ]. The effect of heat treatment on 18Ni300 chromium electroplated coatings is the result of a single-scale action involving complex mechanisms of phase transition kinetics, crystal defect evolution and interfacial metallurgical reactions. It is difficult to enhance the service performance of the plating layer by regulating the heat treatment parameters to achieve the precise release of internal stresses and the optimal matching of microstructure. The 600°C/70MPa hot isostatic pressing treatment on the surface of the SLM18Ni300 substrate had a significant effect on the microstructural evolution of the chromium electroplated layer. As shown in Fig. 5 , the microstructural characteristics show that the flatness of the outer surface of the plating layer is fair, and the bonding state with the substrate is relatively straight, and there are more holes inside the plating layer, and the densification is poor, but the distribution of obvious transverse and longitudinal cracks is not found. The diffusion and creep mechanisms are mainly related to the intrinsic mechanism when hot isostatic pressure is applied to the chromium plating layer. Plastic deformation occurs in the material around the holes and cracks due to the presence of stress gradients under the dual action of high temperature and isotropic isostatic pressure. This plastic deformation effectively promotes hole closure as well as crack repair, and reconfigures the internal defect network of the plated layer through a multiscale material migration mechanism. The process exhibits a typical three-stage dynamics driven by thermodynamics: the initial stage is dominated by particle rearrangement to achieve an initial reduction of porosity through grain boundary sliding and dislocation slip; the subsequent plastic deformation-dominated phase forms a dumbbell-shaped dynamic recrystallization region where the material around the holes undergoes creep flow under the stress gradient; and the final stage is dominated by diffusional creep to achieve pore closure through atomic vacancy migration [ 48–50]. 48–50]. The holding temperature of 600°C and the pressure of 70 MPa are far from the temperature conditions near the melting point of the material. Neither the alloy matrix nor the plating layer has melted, and it is likely to remain only in the stage of interparticle accumulation and rearrangement or plastic deformation. The diffusion of atoms into each other is an example of the action of temperature and pressure, but the relatively low temperatures result in limited diffusion capacity of the atoms to accomplish complete healing of the defects. The insufficiently utilized thermal isostatic pressure effect repairs and closes most of the elongated cracks, but it does not provide enough energy and driving force to induce structural adjustments and defect repair within the layer, resulting in the presence of a large number of holes in the layer. These microscopic mechanisms ultimately determine the macroscopic properties of the coating. During the 1150/150 MPa hot isostatic pressing process carried out on the surface of SLM18Ni300, the microstructural evolution of the chromium plating layer demonstrated an obvious regular transformation phenomenon. As observed by the microstructure in Fig. 6 , the outer surface of the plating layer well maintained the surface flatness characteristics under the dual action of high temperature and high pressure, and formed a dense and straight bonding interface region with the substrate. The existence of such interface characteristics creates favorable physical environment conditions for the defect repair process. In terms of the defect behavior mechanism, the dynamic changes of cracks and holes are in line with the characteristics of thermodynamically driven reversible processes: defects in the nanoscale range can achieve self-healing effects by means of the vacancy diffusion mechanism through the atom migration triggered by thermal activation; whereas, when the defect size increases or the density is elevated, the defects need to rely on the additional driving force factor provided by the thermal isostatic pressure [ 50 – 52 ]. When the temperature reaches 1150°C, together with the continuous action of 150 MPa pressure, the system is brought into the typical diffusion creep dominated phase. At this time, the significantly intensified atomic lattice diffusion and grain boundary slip phenomena lead to a significant decrease in strain rate, and the creep deformation accounts for much more than the plastic deformation component. This situation provides the necessary kinetic conditions to support the hole closure process. Under the dominance of the diffusion creep mechanism, it is observed that the atoms carry out a directional migration behavior along the direction of the concentration gradient toward the hole center, filling the defect space region through the material transport process. Meanwhile, the high-pressure environment effectively suppresses the crack extension tendency, which contributes to the release effect of the lattice distortion energy at the interface. The isotropic homogeneous static pressure field under high temperature conditions accelerates the long-range diffusion process of solute atoms between dendrites, which reconstructs the defect distribution and phase composition of the coating on the atomic scale. 3.2 Phase Analysis As shown in Fig. 7 , under different process conditions carried out on the surface of the SLM18Ni300 substrate, the bonding area of the electrochromium plating layer exhibits obvious phase differences. The presence of Fe-Ni phase, Fe 7 NiCr 2 phase and monolithic Cr phase is mainly detected in the untreated chromium plating specimen, in which the monolithic Cr phase, as a “residual phase” that is not involved in the thermochemical reaction, reflects the fact that the system is thermodynamically inactive in the untreated state, and that the reaction between the elements is incomplete. After heat treatment, the physical phase of the plated specimen is transformed into Fe-Ni phase, Fe-Cr phase, Fe-Ni-Cr phase and a mixture of single Fe, Ni and Cr phases. The heat treatment process allows the atoms to obtain higher thermal activation energy states, and the plated atoms are able to diffusely migrate across the interfacial energy barriers to the base alloy, while the base alloy atoms also migrate in the reverse direction to the plated region due to the concentration gradient. This bidirectional atomic migration behavior builds up an active reaction field, and through the electron orbital hybridization and lattice reconstruction process, Fe, Cr, Ni atoms form Fe-Cr, Fe-Ni-Cr and other new phases of the generation phenomenon, which can be essentially regarded as a direct result of the atomic diffusion dynamics under high temperature conditions and thermodynamic equilibrium together. After 1150/150MPa hot isostatic pressure treatment of plating samples, the main phase of Fe-Ni compounds, Fe-Cr compounds, Fe-Ni-Cr compounds and Fe 7 NiCr 2 compounds, such as intermetallic compounds, the monomer phase completely disappeared. It can be seen that this transformation stems from the special mechanism of the hot isostatic pressing process: the high temperature environment provides the necessary driving force for atomic diffusion, and the isotropic static pressure not only significantly shortens the atomic diffusion path length, but also accelerates the rate of material exchange through the pressure-induced displacement effect of the vacancies. Under the synergistic effect of temperature and pressure, the interatomic bonding force undergoes a reconstruction phenomenon, and the lattice distortion energy is released through the diffusion process, which leads to the participation of all metal atoms in the reaction process and the final formation of stable intermetallic compound structures. The evolution of the process from heat treatment to hot isostatic pressing shows that the optimization of the coating phase from monomer residue to intermetallic compound dominated is successfully achieved by regulating two key factors, namely, the diffusion behavior characteristics of the atoms and the kinetic parameters of the interfacial reaction. As shown in Fig. 8 , the EDS spectroscopy data of the plated layer system on the surface of the SLM18Ni300 specimen are presented. Two micro-area locations in the plating area (measurement point 1 and 2) and the base alloy area (measurement point 3) were selected for elemental quantification, and the experimental data showed that the atomic percentage of Cr element was detected in the plating area without post-treatment as high as 92% or more, and the content of Fe element was extremely low. This shows that the plating process has successfully realized the high-purity directional deposition effect of the Cr element. The elemental composition of the substrate area corresponds to that of the 18Ni300 raw material, in which the element Fe occupies the main component. This demonstrates that the plating process has not significantly altered the original distribution of elements within the substrate. The Cr content at measurement point 1 (in the most superficial layer of the plating) and at measurement point 2 (in the area of the plating-substrate interface) show a high degree of consistency. This phenomenon suggests a directional migration of Cr atoms into the superficial regions of the substrate during the plating process, which is influenced by the microstructural characteristics of the SLM18Ni300 substrate: a high density of dislocation networks and subgranular structures are formed during the SLM forming process, which provide preferential diffusion paths for Cr atoms. The activation energy required for atomic migration in the interfacial region is significantly reduced compared to conventional forged substrates, and the Fe3O4 nanoclusters distributed on the surface of the SLM substrate act as catalytic activity centers, which contribute to the nucleation kinetics of the Cr atoms by lowering the deposition overpotential. Some of the nascent Cr atoms penetrated and diffused into the matrix grain boundaries and dislocation regions driven by the concentration gradient force and interfacial stress field. From the above analysis, it can be seen that the synergistic effect of the microscopic defect structure of the SLM substrate and the electroplating electrochemical behavior not only enhances the metallurgical bonding strength between the plating layer and the substrate, but also forms the gradient structure characteristic of continuous compositional changes in the interfacial transition zone. This special state of atomic concentration distribution provides favorable conditions for the formation of intermetallic compounds during the subsequent hot isostatic pressing process. As shown in Fig. 9 , the EDS micro-area analysis results of the plated layer on the surface of the SLM18Ni300 specimen after hot isostatic pressing treatment at 600°C/70MPa are presented. Four characteristic measurement points (points 1 to 4) in the gradient region of the interface between the plating layer and the substrate were selected, and the quantitative analysis of the elements was carried out. Special atomic diffusion phenomena and interfacial reaction behaviors under high temperature and high pressure environment were revealed by this experimental data. In the outer region of the layer, about 500 µm from the interface, where point 1 is located, 73.7% of Cr and 23.4% of Fe are detected, a 3:1 atomic ratio is established, and the formation of Cr-dominated solid solution phases is obvious, while the limited dissolution of Fe occurs at the same time. The Cr content is found to be decreasing, while the Fe content above 65.5% remains stable, as the measurement points are selected in the matrix direction. Trans-interfacial migration behavior of multiple alloying elements in the hot isostatic pressing process, this distribution feature can be illustrated as an example. 600 ℃ high temperature conditions of Cr atomic diffusion coefficient of the enhancement of the realization of the 70MPa isotropic isostatic compression of the application of stresses so that the grain boundary diffusion activation energy to reduce the role of the generation. It can be seen that the original dislocation channels and subgranular boundaries of the SLM substrate become the fast migration path of atoms, and at the same time, the reverse diffusion of Fe atoms in the substrate to the inside of the plating layer occurs under the combined effect of the concentration gradient and the induction of stress. The fluctuation phenomenon of atomic ratio was found to be associated with the formation of intermetallic phases with different crystal structures by EDS detection. The presence of a high-temperature and high-pressure environment increases the amplitude of atomic vibrations and changes the degree of electron cloud overlap. The rearrangement of orbital electrons is thus triggered, and the FeCr alloy phase characterized by strong covalent bonds is formed. The structural basis for co-eluting in the interfacial region is thus laid down. The enrichment of Ni observed at measurement point 3 is revealed, which is related to the distribution of pristine Ni in the SLM matrix, and the pressure-induced grain boundary migration during hot isostatic pressing. The aggregation of Ni atoms to low-energy positions in the interfacial region is facilitated under high-pressure conditions, and nanoscale clusters are formed as a result. a further lowering of the nucleation barriers of the FeCr phase is realized. The limited extent of diffusion is then manifested by the constraints of treatment temperature and pressure. Although the temperature of 600°C significantly increases the atomic activity, below the austenitization temperature of 18Ni300, full recrystallization does not take place in the matrix, and residual columnar grain boundaries continue to act as diffusion barriers.The long-range migration of the Cr atoms is thus limited. The interdiffusion phenomenon induced by the hot isostatic pressing technique is characterized by controllability, and a reactive layer structure is built up in the interfacial region. The problem of abrupt interfacial defects, which are present in conventional plating processes, is avoided, and examples show that intermetallic compounds play an important role through diffusion reinforcement effects. As a mechanical buffer layer, the crack extension resistance of the plated layer is significantly improved, which is fundamentally different from the pure temperature-driven diffusion process. Not only is there isostatic stress as the driving force for material transport, but the regulation of crystal defect trajectories is even more critical. The elemental distribution state and phase structure characteristics are precisely controlled in the interface region, and this control effect is verified by experimental data. The results of EDS microzone analysis of the plated layer after hot isostatic pressing treatment at 1150°C/150 MPa are shown in Fig. 10 . Three typical areas with gradient distribution characteristics in this plating system are selected for elemental quantitative analysis. Located at the outermost part of the plating layer is point 1 area, which is characterized by the enrichment of Cr element, where the atomic content ratio of Cr to Fe is close to 3:1. This area carries the main responsibility of corrosion protection function, and the high Cr ratio is in line with the expected compositional requirements of the plating layer design. Deeper into the bonding interface (point 2 area) from the plating layer to the substrate direction, the Cr/Fe atomic ratio gradually decreases to about 1.2:1, compared with the aforementioned outer area where the Cr content is significantly attenuated. Examples show that the formation of this composition gradient is closely related to the diffusion of cross-interface atoms during the hot isostatic pressing process, and the mechanistic explanation is attributed to the fact that in the high-temperature and high-pressure coupling field, the Cr atoms in the plating layer obtain sufficient activation energy and overcome the interfacial energy barrier to migrate to the substrate side, and at the same time the Fe atoms in the substrate diffuse in the reverse direction, and the transitional metallurgical bonding zone is generated by the composition. In this case, the ratio of Cr to Fe content tends to be 1:1, revealing that the interface initially realizes the atomic scale interdiffusion layer, which provides compositional conditions for the generation of stable intermetallic compounds. If the heat-affected zone of the substrate (i.e., point 3 region) is further explored, the Cr/Fe atomic ratio decreases to 1:4, while the Cr element still maintains a high level of 18.0%. This phenomenon reveals a unique feature of the enhanced diffusion mechanism of the hot isostatic process: the synergistic effect of the pressure gradient and the chemical potential gradient in the high-pressure, which results in the directional migration of Cr atoms obtaining an extra drive to increase the net flux, thus retaining a stable intermetallic layer far away from the interface in the substrate region. The matrix region away from the interface retains a robust Cr elemental reservoir. This compositional modulation induced by thermal isostatic pressure operation builds up a gradient interfacial layer of continuous compositional transition between the plating layer and the substrate, where the Cr concentration gradually decays with the enhancement of the distance from the interface from the outer high-Cr plating layer, to the interfacial interdiffusion reaction layer, and to the Cr penetration zone in the heat-affected zone of the substrate. At the same time, the mobilization of atomic migration under high pressure not only strengthens the interfacial bonding strength, but also stabilizes the expansion of intermetallic compounds and optimizes the stability of the interfacial structure of the plating system. In the heat-affected zone Cr non-equilibrium state aggregation, coinciding with the pressure-induced expansion plus high-temperature activation of the mobilization of the parallel implementation of the role of the common influx of so, this cross-scale component manipulation mechanism, the experimental construction of the bonding performance of the plating layer to provide support for the theory of the supply and practical verification of the effect. 3.3 Microhardness Microhardness distribution characteristics in different post-treatment process conditions SLM molding 18Ni300 surface plating plating layer, as shown in Fig. 11 . 223.3 HV 0.2 ± 10% for the original SLM molding substrate exhibits the average hardness value, additive manufacturing process in the formation of substable tissue structure and the existence of residual stress state, this phenomenon is in line with it. When the surface plating of pure chromium plating is implemented, the average hardness of the plated specimens is increased to 350.0 HV 0.2 ±10%, and the hard-phase strengthening effect of the plating itself is thus manifested. Gradient distribution characteristics are significantly presented in the hardness of the plating, after 600 ℃ / 70MPa hot isostatic pressing treatment, the peak near the interface bonding appeared in the hardness test results, along the direction of the outer layer of the plating gradual attenuation of the hardness change trend. The occurrence of interfacial metallurgical reactions during hot isostatic pressing is closely related to this phenomenon: selective activation occurs in the atomic diffusion process between the plating layer and the substrate at medium temperature and high pressure, and the formation of the compositional transition zone originates from the migration of Cr atoms to the substrate side in conjunction with the reverse diffusion of Fe atoms. The orderly precipitation of stable intermetallic compounds is promoted, and the diffuse distribution of these hard phases at grain boundaries and dislocations effectively hinders the dislocation motion, resulting in an increase in local hardness. The increase in material densities occurs simultaneously with the significant compaction of holes and microcracks within the tissue under high pressure, and the reduction of indentation size effects in the hardness test is indirectly manifested in the enhancement of the macrohardness. When the hot isostatic pressing process parameters were increased to 1150°C/150 MPa, even better hardness properties were demonstrated in the coating system, with a maximum hardness value of 673.1 HV 0.2 ± 10%. The overall hardness range of 406.3-673.1 HV 0.2 ± 10% was significantly higher than that of the other process groups. The cross-scale interfacial modulation under the synergistic effect of high temperature and high pressure is the source of this strengthening effect: sufficient activation energy for atomic migration is provided at high temperatures, and the significant increase in the depth and extent of the interdiffusion of Cr and Fe atoms results in the formation of eutectic reaction layers of greater thickness at the interface. A significant increase in the volume fraction of nanoscale intermetallic compounds is seen in this process. The formation of fine-grained reinforced structures is promoted by the high-pressure environment while the abnormal grain growth is suppressed. The reduction of crystal defect density leads to the enhancement of lattice distortion, which results in the increase of plastic deformation resistance of the material. 1150℃/150MPa process of the plating-substrate interface mechanical bonding to the metallurgical bonding occurs, hot isostatic pressure-induced interfacial reaction mechanism of reinforcement not only to improve the overall hardness of the plating layer, the gradient hardness distribution of the design of the composite system to optimize the load-bearing capacity and fatigue resistance. Optimization. 3.4 Analysis and Discussion In the context of contemporary materials processing, the development of selective laser melting technology has led to revolutionary changes in the field of preparation processes. A typical example is the 18Ni300 martensitic aging steel, where a special preparation process leads to a surface chromium electrodeposition behavior that is significantly different from that of conventional forming substrates. In contrast to the homogeneous equiaxial crystalline organization of forged or cast 18Ni300, the 18Ni300 substrate manufactured using the SLM process forms a multi-scale microstructure including cellular dendritic crystals, substable phases, and subgranular grain boundaries under rapid solidification conditions. The existence of microstructural variability has a decisive influence on the distribution of surface dislocations and the degree of chemical activity. The SLM18Ni300 surface, which exhibits a high-density dislocation network and activated chemical state, provides a rich cluster of high-energy sites for the chromium electrochemical deposition process, and chromium atoms can be seen to preferentially nucleate in these high-energy regions. On the contrary, the homogeneous equiaxial crystal structure of the conventional molding 18Ni300 material maintains the dislocation density at a low level, and the chemical activity is stabilized, which shows that the chromium nucleation sites are not only limited in number but also uniformly distributed, and the nucleation process is mainly governed by the conventional electrochemical driving force mechanism. The layerwise thermal gradient effect strongly influences the characteristics of the residual stress distribution within the SLM18Ni300 material. The generation of localized strain fields is thus triggered, showing a non-uniform state in the internal regions of the material. It is due to this strain field that the kinetic behavior of ion adsorption changes during the electrodeposition process. The surface ion adsorption process and migration paths are shifted in favor of the Cr ions to reach the suitable deposition sites more rapidly. This shows that the coating growth process is significantly regulated. In the 18Ni300 alloy prepared by the conventional molding process, there is no such local strain field induced by the layerwise thermal gradient. Ion migration following the conventional electrochemical adsorption mechanism is observed in these materials, and the surface deposition process is relatively smooth. The Cr deposition behavior present on the surface of conventionally molded 18Ni300 alloys with greater difficulty in initiation is observed, attributed to the lackluster characteristics of the nanoscale catalyst. Significantly higher values of critical overpotential were observed for this process. In sharp contrast to conventional materials, the high surface roughness characteristic of SLM18Ni300 poses a clear challenge to the chromium electroplating process. Pore formation tends to occur on rough surfaces, and examples show that this can further lead to coating delamination. The optimization of pre-plating processes, such as electrolytic polishing and pulsed laser remelting, is therefore of particular importance, as the application of these techniques results in a significant improvement of the surface roughness and mitigates the negative effects of porosity. Conventional molding 18Ni300 usually shows a low surface roughness index value, and its dependence on the pre-plating treatment is relatively weak. Hot isostatic pressing technology for SLM18Ni300 martensitic aging steel chrome plating layer shows a unique effect, compared with the traditional heat treatment process 18Ni300 chrome plating layer of the case, there are significant differences in the molding characteristics and performance enhancement dimensions. The hot isostatic pressing process, which lasts for 3 hours at a high temperature of 1150°C and a high pressure of 150 MPa, fundamentally realizes the reconstructive transformation of the chromium-plated SLM18Ni300 substrate-layer interface. The induction of microstructure homogenization and the activation effect of intermetallic phase formation work together to make the hardness of the plated layer break through the limiting value of the traditional electroplating process. The inter-element diffusion phenomenon is enhanced by HIP induction, and the two synergistic pathways strongly promote the nucleation process of Cr-Fe intermetallic phase. As a result, the atomic mobility is greatly enhanced by HIP, and the diffusion of Fe atoms from the base alloy to the plated layer is significantly accelerated, an accelerating effect that is difficult to achieve in conventional heat treatments. Due to the limitation of temperature and pressure conditions, the enhancement of atomic mobility in the traditional heat treatment process is limited, and the slowing down of Fe atom diffusion rate is obvious, which is not conducive to the rapid formation of intermetallic phase. Figure 12 shows the schematic principle of 18Ni300 chromium plating before and after different treatments. The FeCr intermetallic compound-rich bonding zone is formed in the HIP-treated sample, and its measured Vickers hardness value reaches 673.1HV0.2 ± 10%, which is upgraded by 90–95% compared with the untreated sample. At the same time, the original dendritic structure of SLM was transformed by HIP treatment, and an isometric crystal structure with twinned grain boundaries was generated. This transformation of grain boundary structure is of great value significance, providing a low-energy channelization path for Cr atom migration [ 49 – 52 ]. The grain boundary structure of 18Ni300 during conventional heat treatment produces a certain degree of change, but it is not able to form the ideal structural characteristics that are favorable for chromium atom migration and plating growth as in the case of HIP treatment. Residual compressive stresses are generated and play a key role in the HIP process. The dislocation-assisted Cr/Fe interdiffusion process is significantly facilitated by this stress. In contrast, the stress state generated by conventional heat treatment is complex and difficult to be precisely regulated, and it is not possible to form a stable stress environment that promotes the formation of intermetallic phases. This shows that the formation of substable Cr-Fe compounds in the 18Ni300 chromium plating layer after conventional heat treatment is difficult and the number of phenomena is small. The mechanism of the influence of hot isostatic pressing on the formation of SLM18Ni300 chromium electroplated coatings is fundamentally different from that of conventional heat treatment. These differences make the HIP-treated SLM18Ni300 chrome plating show significant performance advantages. 4. Conclusion This study focuses on the post-treatment strengthening effect of electrochromium plating coatings on the surface of additively fabricated 18Ni300 alloy, revealing the mechanisms by which different processes affect the microstructure and properties of the coatings. Transverse crack networking and delamination phenomena were observed in the tissue evolution of the coatings after heat treatment, while a flatter electrochromium plating and substrate bonding state appeared after hot isostatic pressing treatment. (1) The synergistic effect of solidification defects during the additive manufacturing process caused a lack of surface integrity of the substrate.223.3 HV 0.2 ±10% is the average hardness value of the SLM molded substrate. There is a deterioration in the flatness and roughness of the pure chromium plating without post-treatment.The Fe-Ni phase, FeNiCr phase, and the residual phase of monomeric Cr that is not involved in the reaction constitute its main phase composition, and the lack of thermodynamic activity of the system leads to the problem of incomplete elemental reaction. (2)The plated layer shows complex microstructure responsiveness after heat treatment, presenting transverse crack network and delamination phenomenon.600℃/70MPa hot isostatic pressure treatment can make the surface of the plated layer flatter and the interface straightness can be maintained, but more holes are still present in the interior, and the densification needs to be further improved. The physical phase of the plated layer was transformed into Fe-Ni/Fe-Cr/Fe-Ni-Cr alloy phase and monolithic Fe/Ni/Cr mixed state. (3) Significantly optimized plating properties were achieved by the 1150°C/150MPa hot isostatic pressing process: maintaining good surface flatness was achieved, and the formation of a dense and flat bonding interface with the substrate was possible. The hardness range is increased to 406.3-673.1HV 0.2 ±10%, with a maximum hardness value of 673.1HV 0.2 ±10% outperforming the other treatment groups, and the monolithic phase of the plating disappears completely. Assume the main corrosion protection function of the outer Cr element-enriched area of Cr/Fe atomic ratio of 3:1, down to 1.2:1 at the bonding interface Cr/Fe ratio shows that the example shows that the interface area atomic scale interdiffusion has been realized. The implementation of the hot isostatic pressing treatment technique has significantly improved the modulation of the atomic diffusion behavior at the interface between the plating and the substrate. The strengthening of the metallurgical bonding state is clearly visible, and the phenomenon of crack formation is significantly suppressed. The trend of hardness index enhancement was confirmed by experimental data. Declarations Funding The author thanks the financial support provided by the Jiangxi Key Laboratory of Green General Aviation Power (GrantNo. Ef202480368). Corresponding author: Yong Li, E-mail: [email protected] Author Contribution Wei Xu , Xiangli Liu and Yong Li wrote the main manuscript text and Guoyang Zhao，Gaojian You prepared the funding. All authors reviewed the manuscript. Data Availability All data supporting the research in this paper are available in the main text and Supplementary Information. References Mei, L. et al. Performance Study and Heat Treatment Analysis of Selective Laser Melting SiC/18Ni300 Martensitic Mold Steel Composites[J]. J. Mater. Eng. Perform. 34 (5), 3827–3842 (2025). Sohail, S. & Reddy, B. C. M. 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Engineering: A . 845 , 143209. https://doi.org/10.1016/j.msea.2022.143209 (2022). Yener, T. et al. Interdiffusion-controlled intermetallic growth in high-pressure processed coating systems[J]. Mater. Charact. 196 , 112596. https://doi.org/10.1016/j.matchar.2022.112596 (2023). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6815548","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":473169978,"identity":"4dd9b987-988c-4210-9c8b-75755a821d1c","order_by":0,"name":"Wei Xu","email":"","orcid":"","institution":"Chengdu Aeronautic Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Xu","suffix":""},{"id":473169979,"identity":"caaf5c5a-4883-4534-9d07-f38fb635f847","order_by":1,"name":"Xiangli Liu","email":"","orcid":"","institution":"Shanxi Datong University，","correspondingAuthor":false,"prefix":"","firstName":"Xiangli","middleName":"","lastName":"Liu","suffix":""},{"id":473169980,"identity":"ed8763e4-a7b7-4437-a32c-6bf832ea4a0c","order_by":2,"name":"Yong Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYBACfvmD7Z//GNjUs7E3EKlFcgbzMQaegrQEPp4DRGoxuMGWxsDz4XCCnEQCsS673WP2QMLgcB6b5OONNxhqbKIJ6mCcc8bcwMAgvZhNOq3YguFYWm4DIS3MDDkGEgkG1oxt0jlmEowNhwlrYQNpOWDAzNgmeYZILTwSaWmSDQbOiW0SPERqkeA5fNiYwSDNmI0H6JcEYvxif7yx8THDHxs5+fbDG298qLEhrAUZGBAfNQgtpOoYBaNgFIyCkQEAn2g7rRA1M4AAAAAASUVORK5CYII=","orcid":"","institution":"Chengdu Aeronautic Polytechnic","correspondingAuthor":true,"prefix":"","firstName":"Yong","middleName":"","lastName":"Li","suffix":""},{"id":473169981,"identity":"d52a4f09-b3c1-43bc-96d9-a93589b5f073","order_by":3,"name":"Guoyang Zhao","email":"","orcid":"","institution":"Chengdu Aeronautic Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Guoyang","middleName":"","lastName":"Zhao","suffix":""},{"id":473169982,"identity":"ef80e486-4f2b-449f-b2dc-3937d48dabe1","order_by":4,"name":"Gaojian You","email":"","orcid":"","institution":"Jiangxi Key Laboratory of Green General Aviation Power","correspondingAuthor":false,"prefix":"","firstName":"Gaojian","middleName":"","lastName":"You","suffix":""}],"badges":[],"createdAt":"2025-06-04 02:53:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6815548/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6815548/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85073099,"identity":"bb502601-d21f-4410-b2e2-c8e6d6459a4a","added_by":"auto","created_at":"2025-06-20 15:59:49","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":95991,"visible":true,"origin":"","legend":"\u003cp\u003eThe giagram of the equipment used in the experiment. (a) Scanning electron microscope, (b) Resistance furnace.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/698f117578b3e30085f3fd06.jpg"},{"id":85073102,"identity":"38df4637-0181-438d-902d-8c7e27590af5","added_by":"auto","created_at":"2025-06-20 15:59:49","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":221691,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of SLM18Ni300. (a) 2000×(Magnification), (b) 3000×, (c) 4000×, and (d) 5000×.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/189820490cd0209695fc6543.jpg"},{"id":85073553,"identity":"2c589948-4020-4d37-9a06-b0b841e09167","added_by":"auto","created_at":"2025-06-20 16:07:49","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":53720,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of SLM18Ni300. (a) 100×(Magnification), (b) 200×.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/4b65d283121d7a4c1e297ce5.jpg"},{"id":85073554,"identity":"5db870a6-2769-44ba-8fe0-bb70b8aa194c","added_by":"auto","created_at":"2025-06-20 16:07:49","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":142395,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of the heat-treated SLM18Ni300 electroplated coating. (a) 100× (magnification), (b) 200×, (c) 300×, (d) 400×.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/3b9d90d36619fca416e2af94.jpg"},{"id":85073560,"identity":"75341000-114f-4fe8-8f85-29fdd8395add","added_by":"auto","created_at":"2025-06-20 16:07:50","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":176236,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of SLM18Ni300 electroplated coating under hot isostatic pressure at 600℃/ 70MPa . (a) 100× (magnification), (b) 200×, (c) 300×, (d) 400×.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/c30d9ebf7c9ad112452b985b.jpg"},{"id":85074178,"identity":"f261c2e8-f59c-419d-8dda-c3ce05ce6283","added_by":"auto","created_at":"2025-06-20 16:15:50","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":101700,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of SLM18Ni300 electroplated coating under hot isostatic pressure at 1150℃/ 100MPa. (a) 100× (magnification), (b) 200×, (c) 300×, (d) 400×.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/8ad767d5d17c7854907abefc.jpg"},{"id":85073103,"identity":"95878eb8-b43d-4c55-b76a-d2088ad06f5a","added_by":"auto","created_at":"2025-06-20 15:59:49","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":28039,"visible":true,"origin":"","legend":"\u003cp\u003ePhase analysis at the coating junction.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/8d8a29bad7ca8cbfec69935f.jpg"},{"id":85073113,"identity":"27795650-08d6-49e5-ad36-a7eece3d2a14","added_by":"auto","created_at":"2025-06-20 15:59:50","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":527887,"visible":true,"origin":"","legend":"\u003cp\u003eEDS spectrum analysis of 18Ni300 electroplated coating (a) The coating elements are distributed in 3 regions, (b) EDS spectral analysis in point 1 region, (c) Point 2 region, (d) Point 3 region.\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/4ff34638d437df8bddc53eda.jpeg"},{"id":85073116,"identity":"76d44bb4-149a-43bf-b5d5-c51d856a4fc6","added_by":"auto","created_at":"2025-06-20 15:59:50","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":696281,"visible":true,"origin":"","legend":"\u003cp\u003eEDS spectrum analysis of SLM18Ni300 electroplated coating under hot isostatic pressure at 600℃/ 70Mpa.(a) The coating elements are distributed in 4 regions, (b) EDS spectral analysis in point 1 region, (c) Point 2 region, (d) Point 3 region, (e) Point 4 region.\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/01e6e5e73f7a536b7eb2981e.jpeg"},{"id":85073111,"identity":"430e6238-5d62-4a57-88f9-2df361f32bdc","added_by":"auto","created_at":"2025-06-20 15:59:50","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":78673,"visible":true,"origin":"","legend":"\u003cp\u003eEDS spectrum analysis of SLM18Ni300 electroplated coating under hot isostatic pressure at 1150℃/100Mpa.(a) The coating elements are distributed in 3 regions, (b) EDS spectral analysis in point 1 region, (c) Point 2 region, (d) Point 3 region.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/c8a5c2ffb9c884f6fd1b65f8.jpg"},{"id":85073562,"identity":"f5f4d43e-fa13-4b5d-aded-2686718c5a1c","added_by":"auto","created_at":"2025-06-20 16:07:50","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":37518,"visible":true,"origin":"","legend":"\u003cp\u003eMicrohardness analysis of the coating.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/3b5b72eaa735b64cc39256d3.jpg"},{"id":85074180,"identity":"d16cc8b8-d0ab-4cc0-82b4-6c527d9a849f","added_by":"auto","created_at":"2025-06-20 16:15:50","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":74155,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the principle of post-treatment 18Ni300 chromium plating layer.\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/0a91c1f5ebb8e803b7db208c.jpg"},{"id":88851508,"identity":"be7ad536-88d6-4981-b240-59f33f640441","added_by":"auto","created_at":"2025-08-12 05:38:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2966178,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6815548/v1/0c397c05-e307-45c0-846a-85af30d3072b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Influence of post-treatment on the performance of SLM forming 18ni300 electroplated coatings","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAs a star material in the field of additive manufacturing, martensitic ageing steels show excellent application potential in Selective Laser Melting (SLM) technology with their unique alloy system. The advantages of high strength, high toughness and excellent process performance make it the material of choice for missile shells, pressure vessels, cold-drawn molds, etc. It occupies an irreplaceable position in the manufacturing of aerospace key load-bearing components, the processing of precision mold cavities, and the manufacturing of high-end equipment under extreme conditions [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. 18Ni300 martensitic aging steel is a new type of steel made by adding Co, Al, M, M and P to the Fe-18Ni alloy. 18Ni300 martensitic steel is formed by adding Co, Al, Mo, Ti and other elements on the basis of Fe-18Ni alloy, and then undergoes aging treatment after solid solution treatment. intermetallic compounds, such as Ni\u003csub\u003e3\u003c/sub\u003eMo, Fe\u003csub\u003e2\u003c/sub\u003eMo, Ni\u003csub\u003e3\u003c/sub\u003eTi and so on, precipitate and precipitate in martensitic region. The material has excellent strength performance and equally outstanding plasticity and toughness, with a yield strength of between 1400\u0026ndash;2400 MPa. Conventional manufacturing methods for producing complex 18Ni300 parts suffer from long production cycles, high costs and insufficient machining accuracy, which limits the wide application of this alloy in many fields [\u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Selected-area laser melting technology is a new rapid prototyping technical method. Computer-aided design at the same time through the laser beam irradiation metal powder melting, layer by layer printing and layer by layer accumulation to achieve the rapid manufacturing of complex parts. The complex structure of the molded parts is not limited, and the ultra-fast cooling rate ensures the superiority of accuracy and performance, while the production cycle is short and low cost [\u003cspan additionalcitationids=\"CR11 CR12 CR13\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. There have been a number of reported examples of domestic and international research on SLM forming of martensitic aged steels.Riccardo Casati et al [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] used laser selective zone melting technology to realize the forming process of 18Ni300 material, and the aging treatment process was applied to the formed specimens. The team's data show that the evolution of the internal organization of the material accompanies the aging process and the precipitation of reinforcing phases, which leads to a significant increase in the strength properties of the alloy, while the plasticity indexes show a decrease. The mechanical properties obtained after aging treatment are comparable to those of conventional forged parts.Kempen K et al [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] focused on the scanning speed and powder thickness of the two key variables, systematically studied the 18Ni300 material microstructure characteristics and mechanical properties of the mechanism of influence, that: too high a scanning speed or too large a thickness of the powder will lead to the deterioration of the material densification index. The laser selective zone melting technology, which is in the stage of continuous optimization, is still facing many challenges. Extreme thermal gradient conditions and transient solidification characteristics are inherent in this process, and the formation of surface defect networks is inevitable during the cumulative build-up process of 18Ni300 alloy layer by layer. The complex coupling of thermodynamic and kinetic factors dominates the melting-solidification process, which is particularly prominent, and process problems such as the tendency of powder spheroidization occur frequently. The combined effect of the above factors significantly increases the difficulty of controlling the forming process, and the negative impact of the generation of pore-type defects on the surface properties has been confirmed by a number of studies [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAt the current stage, the research work on SLM forming 18Ni300 martensitic aging steel is mainly focused on the optimization of forming process parameters and post-treatment technology and other directional exploration. It is worth noting that there is relatively little research in the field of surface modification of SLM forming 18Ni300. Maraging steel surface modification coating preparation method exists a variety of methods, including arc spraying technology, laser cladding process, electroplating treatment and chemical plating and other traditional means. The plating obtained by these methods has a significant effect on the protective function of the base material.\u003c/p\u003e \u003cp\u003eAs a time-honored surface treatment technology, the electroplating process is particularly suitable for surface enhancement of ultra-high-strength steel materials. The wear and corrosion resistance of the chromium plated substrate surfaces were significantly improved [\u003cspan additionalcitationids=\"CR19 CR20 CR21 CR22\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].Sundar et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] showed a significant increase in the fatigue life of 15-5PH ultra-high-strength stainless steel samples pretreated with laser shot peening followed by hard chromium plating compared to the unshot-peened control group. The fatigue cracks sprouted at the microcracks in the plating region, but the direction deflection phenomenon occurred during the expansion to the matrix region, and it is believed that this method can effectively inhibit the continuous expansion of fatigue cracks.Liao et al [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] showed that when different concentrations of nano-silicon nitride particles were doped into the chromium plating solution for electrodeposition under DC conditions, the prepared Cr-C/Si3N4 composite plating layer had special properties. The volume fraction of Si3N4 particles in the plating layer showed a regular change of first increasing and then decreasing with the variability increase of Si3N4 concentration in the plating bath. Samples obtained under specific process parameters showed that the Si3N4 particles could be uniformly dispersed in the distribution of the Cr-C matrix.Bellemare et al [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] conducted a systematic study on the relationship between the densities of chromium plated layers on the surface of AISI4340 steel and hydrogen embrittlement phenomenon. Through the preparation of different current density conditions and whether or not sandblasted specimen group comparison analysis found that: the key factors leading to the occurrence of hydrogen embrittlement phenomenon of 4340 steel is the plating density of the differential performance. Although the chromium plating treatment can significantly improve the wear resistance of the steel surface, the degradation of the matrix fatigue performance is unavoidable. Typically, large residual stresses are generated during the plating process, microcracks are formed inside the chromium plating layer, material properties on both sides of the crack interface are differentiated, deflection and bifurcation phenomena are easy to occur, and the stress intensity factor is reduced at the tip of the crack. When the crack density in the plating layer reaches a high level, the spalling phenomenon is very easy to appear in the actual use process. The development and regulation of new protective technologies such as nano-strengthening and composite plating have been developed through the chromium plating process for many years [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan additionalcitationids=\"CR28 CR29\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. There are relatively few studies on the post-processing of electrochromium plating coatings on steel surfaces, especially for electrochromium plating on SLM-formed 18Ni300 surfaces. Isotropic pressure can be applied by the hot isostatic pressing (HIP) technique, and material pressing and sintering is accomplished under the synergistic effect of temperature and pressure. Optimization of the material organization, elimination of internal defects in the parts and improvement of mechanical properties can be achieved by this technique [\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The internal pore diffusion model of high-temperature alloys was investigated by Epishin et al [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], and the void diffusion occurs at high temperatures and pressures, and the pore defects are effectively repaired.Plessis et al [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] concluded that the SLM molded parts are of excellent quality and very high densities after hot isostatic pressing, and the reduction of surface porosity of the molded parts can be achieved by increasing the pressures and prolonging the holding time. Hot isostatic pressing technology is commonly used in the field of integral forming of complex components and casting densification process, by virtue of the dual action of high temperature and high pressure, internal porosity, shrinkage and segregation defects can be effectively eliminated. For SLM18Ni300 electroplated coatings to carry out hot isostatic pressing post-treatment research work is still in a state of blank. In this paper, a combination of multi-scale experimental means and characterization methods are used to post-treat the SLM18Ni300 electroplated layer in a hot isostatic pressing device. The heat-treated plated layer is used as a control sample to systematically observe the changes in microstructure. The structural composition and performance parameters were also comprehensively tested, thus revealing the influence of hot isostatic pressing technology on the organizational structure and performance characteristics of SLM18Ni300 electroplated coatings. The goal of intelligent regulation and integration of the post-treatment process is expected to be realized through this research, and this breakthrough is expected to promote the technological innovation in the field of high-end manufacturing, and provide a more universal solution for the surface technology in the field of additive manufacturing of high-performance metal materials.\u003c/p\u003e"},{"header":"2. Materials, Equipment and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Test Equipment and Materials\u003c/h2\u003e \u003cp\u003eThis test adopts the DMP Flex350 selective laser melting and forming equipment manufactured by GF, which is equipped with a soft scraper powder feeding system to realize uniform powder laying and efficient recycling, and provide hardware guarantee for high-precision forming. The core component is a 500W fiber laser with a spot diameter of 100\u0026micro;m, capable of delivering stable laser energy. Combined with an adjustable powder thickness of 10\u0026ndash;100\u0026micro;m and a scanning speed of up to 7m/s, the dynamic behavior of the molten pool can be precisely adjusted to meet different molding requirements. The built-in atmosphere control system ensures that the volume fraction of oxygen in the processing environment is always\u0026thinsp;\u0026le;\u0026thinsp;0.0025%, which effectively avoids oxidative contamination of metal powder at high temperature and guarantees the purity of the molded parts. 275mm\u0026times;275mm substrate size provides sufficient space for diversified specimen preparation and supports high-quality molding of complex geometrical structures. The raw material for the test is 18Ni300 maraging steel powder prepared by vacuum aerosol method, which gives the powder excellent sphericity and smooth surface morphology, and significantly improves the fluidity and stacking density of the powder in the process of powder spreading. The particle size distribution of the powder is concentrated in the range of 25\u0026thinsp;~\u0026thinsp;53\u0026micro;m, the Hall flow rate is 13.80s/50g, and the bulk density reaches 4.18g/cm\u0026sup3;, which all meet the strict requirements of the SLM process for the powder fluidity and filling efficiency. Its chemical composition is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, and the precise proportion of each alloying element lays the foundation for the mechanical properties of the subsequent molded parts.\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 compositions of 18Ni300( mass fraction, %)\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\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e17.70\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.31\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003eMargin\u003c/b\u003e\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 Test Scheme\u003c/h2\u003e \u003cp\u003eThe test adopts SLM forming process, the 18Ni300 alloy powder is uniformly preset in the forming chamber of the DMP Flex350 equipment, and the printing program is initiated after the evacuation-argon replacement cycle (high-purity argon purity\u0026thinsp;\u0026ge;\u0026thinsp;99.999%) to construct an oxygen-free environment. Set forming process parameters are as follows: laser power 230W, scanning speed 1100mm/s, scanning spacing 0.1mm, pavement layer thickness of 30\u0026micro;m, in the 275mm \u0026times; 275mm substrate prepared on the specifications of 15mm \u0026times; 15mm \u0026times; 17mm cubic substrate. After the forming was completed, the specimen was separated from the substrate by precise wire cutting, and the surface was sequentially polished and mechanically polished to a mirror state, and then placed in an ultrasonic cleaner with an ethanol solution for 20 min, and then treated with anodic electrode degreasing, deionized water rinsing, and activation, to provide a clean and active surface for chromium electroplating. The plating process adopts constant voltage mode, controlling voltage 4V, current 10A, and the pretreated substrate is immersed into the chromium plating electrolyte and deposited for 5min, and then rinsed with deionized water and dried in the oven at 100℃ for 30min immediately after the end of the process, to obtain the chromium plating intermediate specimen. Subsequently, it was divided into two groups for post-treatment: one group was placed in a hot isostatic press, argon gas was introduced at high temperature and constant pressure was applied, and after holding for 3 hours, it was slowly cooled to room temperature with the furnace to form a hot isostatic strengthening of the plating layer; the other group, as a control, was put into a box-type heat treatment furnace, and after holding for 3 hours at 900\u0026deg;C, it was air-cooled to obtain the conventional heat treatment of plated specimens, and the box-type heat treatment furnace is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b). The main process parameters of the test are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eJSM-IT500 scanning electron microscope equipped with EDS spectrometer is used to observe the microscopic morphology of the interface between the plating layer and the substrate, and the equipment diagram is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a), and the distribution pattern of Cr, Fe and other elements in the interface area is analyzed by line scanning technology; HV-1000A microhardness tester is used to test the hardness of the area near the interface, and the load is set to be 0.2kg and the holding time to be 10s, and the arithmetic mean value is taken to ensure the reliability of the data after eliminating the extreme values. Set the load 0.2kg, holding time 10s, each specimen selected 10 effective measurement points, remove the extreme value to take the arithmetic average to ensure the reliability of the data. The whole test program provides a rigorous experimental basis for revealing the strengthening mechanism of hot isostatic pressing on the chrome-plated layer on the surface of SLM forming 18Ni300 by precisely controlling the process parameters and characterization methods.\u003c/p\u003e \u003cp\u003e \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\u003eMain process parameters of post-treatment after the experiment\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSample No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eHeat treatment process\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c4\"\u003e \u003cp\u003ePost-treatment after hot isostatic pressing\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTemperature /℃\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTime /H\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTemperature /℃\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePressure /MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTime /H\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e900\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\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\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 \u003c/div\u003e"},{"header":"3. Test Results and Discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Microstructure of the coating\u003c/h2\u003e \u003cp\u003eUsing laser selective zone melting (SLM) technology to form 18Ni300 martensitic aging steel is obviously different from the traditional forging or casting alloys of uniform equiaxial crystalline organization, and its microstructure shows a typical fish scale melt channel structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). High-energy laser beam on the powder layer point-by-point melting and rapid solidification process, the higher single-pass molten pool cooling rate formed a dynamic non-equilibrium solidification interface characteristics. The fine columnar crystals extending directionally along the heat dissipation gradient of the melt pool were mainly distributed in the center region of the melt channel (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a)), and the growth direction was approximately perpendicular to the axis of the melt channel. This reflects that the substrate normal direction is the dominant heat flow direction during laser scanning. The complexity of the heat dissipation path and the higher cooling rate of the cellular crystals distributed in the edge region of the channel in direct contact with the unmelted powder lead to an increase in the degree of subcooling. Rapid nucleation and lateral growth of cytosolic nuclei form a uniform and dense microstructure in this region.\u003c/p\u003e \u003cp\u003eThe complexity of the thermal history of the SLM layer-by-layer process is revealed by the coexistence of multiple oriented columnar crystals inside the channel shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). During subsequent channel scanning, the solidified layer undergoes secondary remelting and localized heating. Partial dissolution of the previously formed columnar crystal boundaries occurs, and a deflection of the heat flow direction in the newly solidified region due to the overlapping melt pool results. The formation of the multi-directionally grown columnar crystal structure is finally completed. The junction region in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(d) shows the coexistence of cytosolic and irregular columnar crystals, which is essentially a product of the solidification interface destabilization, and this property is confirmed. In the high cooling rate region at the edge of the channel, the initial formation of cytosolic crystals due to solute enrichment triggers the competitive growth of dendritic arms, which is clearly visible. The subsequent thermal activation of the melt pool captures the transformation of some of the cytosolic crystals by the rapid extension of secondary dendrite arms in the dominant direction. After the elongated columnar crystal transformation is completed, the formation of a polymorphic mixed solidification organization is finally achieved. The significant presence of melt channel size variability shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec is closely related to the interlayer thermal coupling effect unique to selective laser melting technology. Subjected to laser radiation, the lower layer of solidified tissue is reheated above the austenitization temperature when melting of the upper powder layer occurs. A pinned melt channel with a wide upper and narrower lower layer is formed, which gradually decreases the melt pool depth as the number of accumulated layers increases [\u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The laser body energy density has a direct effect on the melt pool behavior, and the laser body energy density can be calculated from Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:E=\\frac{P}{s\\times\\:v\\times\\:t}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere E is the laser body energy density (J/mm\u003csup\u003e3\u003c/sup\u003e), P is the laser power (W), t is the thickness of the powder laying layer (mm), s is the scanning spacing (mm), and v is the scanning speed (mm/s). The laser power and scanning speed are critical for the control of the magnitude of the energy density of the laser body [\u003cspan additionalcitationids=\"CR39\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Insufficient energy to completely melt the powder particles occurs when the laser power is too low or the scanning speed is too fast. The grain boundaries are enriched with unfused defects, including powder residues and half-molten particles. Metal evaporation and spattering phenomena occur at too high a power or too slow a speed, forming porosity defects or spheroidization defects upon cooling [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. It can be seen that the elimination of the surface defect network is difficult to be realized by simply adjusting the energy density. The surface integrity is thereby reduced by the combined effect of micropores formed during solidification, residual stresses, and unfused interfaces. The necessity of surface modification treatments for 18Ni300 materials is particularly evident in the SLM molding process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the microstructure of the pure chromium plating layer presented on the surface of the SLM formed 18Ni300 substrate shows a significant deterioration in both flatness and roughness characteristics. The multidimensional mechanism of the plating layer formation process can be explored in depth. The Cr ion concentration and additive concentration are generally recognized as the most important regulatory parameters that decisively influence the key factors of plating layer quality. The control effect of these parameters, in turn, plays a significant role in governing the flow mass transfer process. In the unstirred plating system, the absence of a forced convection environment makes the transport of Cr ions and additives to the microscopic defective regions dependent only on their own concentration gradients. As the plating time increases and the reactants continue to be consumed, the problem of insufficient material transport becomes apparent. The formation of microcracks is thus induced. The nucleation-growth model can be used as a theoretical basis to explain the electroplating process, as shown in Eq.\u0026nbsp;2:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\omega\\:=Bexp（-\\frac{T}{{\\eta\\:}^{2}}）$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere T is the plating temperature, B is the constant parameter of the copper substrate, ω is the nucleation rate, and η is the cathodic polarization potential [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. When the current condition of 10 mA was set, the cathodic polarization potential showed a decreasing trend, which triggered the phenomenon of decreasing nucleation rate. The initial growth state of the plated layer is significantly affected. The essential process of electrodeposition of chromium involves the gradual deposition of dichromate ions to metallic chromium in the presence of a DC electric field. Four key links constitute the process: diffusion to the electrode surface occurs firstly with dichromate ions; subsequent migration to the interior of the bilayer driven by the electric field, a colloidal film of chromium alkali chromate is formed at the electrode interface; sulfate ions act as a catalyst to promote the dissolution of this colloidal film, which acquires electrons to be converted into adsorbed chromium atoms to realize chromium ions [\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Under the condition of flat substrate surface, the full discharge mode dominates, and the synchronized nucleation phenomenon appears on the steel substrate surface. When obvious concave and convex structures exist on the substrate surface, the raised parts become the concentration area of the discharge, and the partial discharge mode is revealed. The limited number of raised areas and their small size lead to the establishment of a specific correlation between roughness and chromium grain characteristics: a tendency towards finer chromium grain sizes and sparser stacking patterns are observed with increasing roughness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe microstructure evolution of the electrochromium plating layer formed on the surface of SLM18Ni300 substrate after heat treatment presents complex characteristics. The phenomena of transverse crack networking and delamination are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, which can be essentially attributed to the synergistic effect of stress relaxation process and crystal structure reconstruction within the plated layer. During the heat treatment process, the chromium plating layer undergoes three critical transformation stages: martensitic decomposition occurs in the 300\u0026ndash;400 temperature range, leading to volume shrinkage, phase transition stresses superimposed on the quenching residual stresses accumulated during the plating process, and a three-dimensional stress field is thus formed inside the plating layer. 600\u0026deg;C temperature threshold is exceeded, and brittle Fe-Cr intermetallic compound layer is formed at the plating-substrate interface, which has lower shear strength than the substrate material. Its shear strength is much lower than that of the base material, and the dominant channel for crack extension is thus established. The distribution of the thermal stress gradient shows an enhanced trend, and the difference in the coefficients of thermal expansion between the plating and the substrate leads to the phenomenon of interfacial exfoliation during the cooling process. The crack extension path changes from through-crystal mode to along-crystal mode, and the hard and brittle characteristics are strengthened so that the cracks penetrate through the plating layer and invade the matrix, and the typical morphology of \u0026ldquo;plating-substrate hybrid fatigue source\u0026rdquo; is thus formed [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The effect of heat treatment on 18Ni300 chromium electroplated coatings is the result of a single-scale action involving complex mechanisms of phase transition kinetics, crystal defect evolution and interfacial metallurgical reactions. It is difficult to enhance the service performance of the plating layer by regulating the heat treatment parameters to achieve the precise release of internal stresses and the optimal matching of microstructure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe 600\u0026deg;C/70MPa hot isostatic pressing treatment on the surface of the SLM18Ni300 substrate had a significant effect on the microstructural evolution of the chromium electroplated layer. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the microstructural characteristics show that the flatness of the outer surface of the plating layer is fair, and the bonding state with the substrate is relatively straight, and there are more holes inside the plating layer, and the densification is poor, but the distribution of obvious transverse and longitudinal cracks is not found. The diffusion and creep mechanisms are mainly related to the intrinsic mechanism when hot isostatic pressure is applied to the chromium plating layer. Plastic deformation occurs in the material around the holes and cracks due to the presence of stress gradients under the dual action of high temperature and isotropic isostatic pressure. This plastic deformation effectively promotes hole closure as well as crack repair, and reconfigures the internal defect network of the plated layer through a multiscale material migration mechanism. The process exhibits a typical three-stage dynamics driven by thermodynamics: the initial stage is dominated by particle rearrangement to achieve an initial reduction of porosity through grain boundary sliding and dislocation slip; the subsequent plastic deformation-dominated phase forms a dumbbell-shaped dynamic recrystallization region where the material around the holes undergoes creep flow under the stress gradient; and the final stage is dominated by diffusional creep to achieve pore closure through atomic vacancy migration [ 48\u0026ndash;50]. 48\u0026ndash;50]. The holding temperature of 600\u0026deg;C and the pressure of 70 MPa are far from the temperature conditions near the melting point of the material. Neither the alloy matrix nor the plating layer has melted, and it is likely to remain only in the stage of interparticle accumulation and rearrangement or plastic deformation. The diffusion of atoms into each other is an example of the action of temperature and pressure, but the relatively low temperatures result in limited diffusion capacity of the atoms to accomplish complete healing of the defects. The insufficiently utilized thermal isostatic pressure effect repairs and closes most of the elongated cracks, but it does not provide enough energy and driving force to induce structural adjustments and defect repair within the layer, resulting in the presence of a large number of holes in the layer. These microscopic mechanisms ultimately determine the macroscopic properties of the coating.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDuring the 1150/150 MPa hot isostatic pressing process carried out on the surface of SLM18Ni300, the microstructural evolution of the chromium plating layer demonstrated an obvious regular transformation phenomenon. As observed by the microstructure in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the outer surface of the plating layer well maintained the surface flatness characteristics under the dual action of high temperature and high pressure, and formed a dense and straight bonding interface region with the substrate. The existence of such interface characteristics creates favorable physical environment conditions for the defect repair process. In terms of the defect behavior mechanism, the dynamic changes of cracks and holes are in line with the characteristics of thermodynamically driven reversible processes: defects in the nanoscale range can achieve self-healing effects by means of the vacancy diffusion mechanism through the atom migration triggered by thermal activation; whereas, when the defect size increases or the density is elevated, the defects need to rely on the additional driving force factor provided by the thermal isostatic pressure [\u003cspan additionalcitationids=\"CR51\" citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. When the temperature reaches 1150\u0026deg;C, together with the continuous action of 150 MPa pressure, the system is brought into the typical diffusion creep dominated phase. At this time, the significantly intensified atomic lattice diffusion and grain boundary slip phenomena lead to a significant decrease in strain rate, and the creep deformation accounts for much more than the plastic deformation component. This situation provides the necessary kinetic conditions to support the hole closure process. Under the dominance of the diffusion creep mechanism, it is observed that the atoms carry out a directional migration behavior along the direction of the concentration gradient toward the hole center, filling the defect space region through the material transport process. Meanwhile, the high-pressure environment effectively suppresses the crack extension tendency, which contributes to the release effect of the lattice distortion energy at the interface. The isotropic homogeneous static pressure field under high temperature conditions accelerates the long-range diffusion process of solute atoms between dendrites, which reconstructs the defect distribution and phase composition of the coating on the atomic scale.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Phase Analysis\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, under different process conditions carried out on the surface of the SLM18Ni300 substrate, the bonding area of the electrochromium plating layer exhibits obvious phase differences. The presence of Fe-Ni phase, Fe\u003csub\u003e7\u003c/sub\u003eNiCr\u003csub\u003e2\u003c/sub\u003e phase and monolithic Cr phase is mainly detected in the untreated chromium plating specimen, in which the monolithic Cr phase, as a \u0026ldquo;residual phase\u0026rdquo; that is not involved in the thermochemical reaction, reflects the fact that the system is thermodynamically inactive in the untreated state, and that the reaction between the elements is incomplete. After heat treatment, the physical phase of the plated specimen is transformed into Fe-Ni phase, Fe-Cr phase, Fe-Ni-Cr phase and a mixture of single Fe, Ni and Cr phases. The heat treatment process allows the atoms to obtain higher thermal activation energy states, and the plated atoms are able to diffusely migrate across the interfacial energy barriers to the base alloy, while the base alloy atoms also migrate in the reverse direction to the plated region due to the concentration gradient. This bidirectional atomic migration behavior builds up an active reaction field, and through the electron orbital hybridization and lattice reconstruction process, Fe, Cr, Ni atoms form Fe-Cr, Fe-Ni-Cr and other new phases of the generation phenomenon, which can be essentially regarded as a direct result of the atomic diffusion dynamics under high temperature conditions and thermodynamic equilibrium together. After 1150/150MPa hot isostatic pressure treatment of plating samples, the main phase of Fe-Ni compounds, Fe-Cr compounds, Fe-Ni-Cr compounds and Fe\u003csub\u003e7\u003c/sub\u003eNiCr\u003csub\u003e2\u003c/sub\u003e compounds, such as intermetallic compounds, the monomer phase completely disappeared. It can be seen that this transformation stems from the special mechanism of the hot isostatic pressing process: the high temperature environment provides the necessary driving force for atomic diffusion, and the isotropic static pressure not only significantly shortens the atomic diffusion path length, but also accelerates the rate of material exchange through the pressure-induced displacement effect of the vacancies. Under the synergistic effect of temperature and pressure, the interatomic bonding force undergoes a reconstruction phenomenon, and the lattice distortion energy is released through the diffusion process, which leads to the participation of all metal atoms in the reaction process and the final formation of stable intermetallic compound structures. The evolution of the process from heat treatment to hot isostatic pressing shows that the optimization of the coating phase from monomer residue to intermetallic compound dominated is successfully achieved by regulating two key factors, namely, the diffusion behavior characteristics of the atoms and the kinetic parameters of the interfacial reaction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the EDS spectroscopy data of the plated layer system on the surface of the SLM18Ni300 specimen are presented. Two micro-area locations in the plating area (measurement point 1 and 2) and the base alloy area (measurement point 3) were selected for elemental quantification, and the experimental data showed that the atomic percentage of Cr element was detected in the plating area without post-treatment as high as 92% or more, and the content of Fe element was extremely low. This shows that the plating process has successfully realized the high-purity directional deposition effect of the Cr element. The elemental composition of the substrate area corresponds to that of the 18Ni300 raw material, in which the element Fe occupies the main component. This demonstrates that the plating process has not significantly altered the original distribution of elements within the substrate. The Cr content at measurement point 1 (in the most superficial layer of the plating) and at measurement point 2 (in the area of the plating-substrate interface) show a high degree of consistency. This phenomenon suggests a directional migration of Cr atoms into the superficial regions of the substrate during the plating process, which is influenced by the microstructural characteristics of the SLM18Ni300 substrate: a high density of dislocation networks and subgranular structures are formed during the SLM forming process, which provide preferential diffusion paths for Cr atoms. The activation energy required for atomic migration in the interfacial region is significantly reduced compared to conventional forged substrates, and the Fe3O4 nanoclusters distributed on the surface of the SLM substrate act as catalytic activity centers, which contribute to the nucleation kinetics of the Cr atoms by lowering the deposition overpotential. Some of the nascent Cr atoms penetrated and diffused into the matrix grain boundaries and dislocation regions driven by the concentration gradient force and interfacial stress field. From the above analysis, it can be seen that the synergistic effect of the microscopic defect structure of the SLM substrate and the electroplating electrochemical behavior not only enhances the metallurgical bonding strength between the plating layer and the substrate, but also forms the gradient structure characteristic of continuous compositional changes in the interfacial transition zone. This special state of atomic concentration distribution provides favorable conditions for the formation of intermetallic compounds during the subsequent hot isostatic pressing process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the EDS micro-area analysis results of the plated layer on the surface of the SLM18Ni300 specimen after hot isostatic pressing treatment at 600\u0026deg;C/70MPa are presented. Four characteristic measurement points (points 1 to 4) in the gradient region of the interface between the plating layer and the substrate were selected, and the quantitative analysis of the elements was carried out. Special atomic diffusion phenomena and interfacial reaction behaviors under high temperature and high pressure environment were revealed by this experimental data. In the outer region of the layer, about 500 \u0026micro;m from the interface, where point 1 is located, 73.7% of Cr and 23.4% of Fe are detected, a 3:1 atomic ratio is established, and the formation of Cr-dominated solid solution phases is obvious, while the limited dissolution of Fe occurs at the same time. The Cr content is found to be decreasing, while the Fe content above 65.5% remains stable, as the measurement points are selected in the matrix direction. Trans-interfacial migration behavior of multiple alloying elements in the hot isostatic pressing process, this distribution feature can be illustrated as an example. 600 ℃ high temperature conditions of Cr atomic diffusion coefficient of the enhancement of the realization of the 70MPa isotropic isostatic compression of the application of stresses so that the grain boundary diffusion activation energy to reduce the role of the generation. It can be seen that the original dislocation channels and subgranular boundaries of the SLM substrate become the fast migration path of atoms, and at the same time, the reverse diffusion of Fe atoms in the substrate to the inside of the plating layer occurs under the combined effect of the concentration gradient and the induction of stress. The fluctuation phenomenon of atomic ratio was found to be associated with the formation of intermetallic phases with different crystal structures by EDS detection. The presence of a high-temperature and high-pressure environment increases the amplitude of atomic vibrations and changes the degree of electron cloud overlap. The rearrangement of orbital electrons is thus triggered, and the FeCr alloy phase characterized by strong covalent bonds is formed. The structural basis for co-eluting in the interfacial region is thus laid down. The enrichment of Ni observed at measurement point 3 is revealed, which is related to the distribution of pristine Ni in the SLM matrix, and the pressure-induced grain boundary migration during hot isostatic pressing. The aggregation of Ni atoms to low-energy positions in the interfacial region is facilitated under high-pressure conditions, and nanoscale clusters are formed as a result. a further lowering of the nucleation barriers of the FeCr phase is realized. The limited extent of diffusion is then manifested by the constraints of treatment temperature and pressure. Although the temperature of 600\u0026deg;C significantly increases the atomic activity, below the austenitization temperature of 18Ni300, full recrystallization does not take place in the matrix, and residual columnar grain boundaries continue to act as diffusion barriers.The long-range migration of the Cr atoms is thus limited. The interdiffusion phenomenon induced by the hot isostatic pressing technique is characterized by controllability, and a reactive layer structure is built up in the interfacial region. The problem of abrupt interfacial defects, which are present in conventional plating processes, is avoided, and examples show that intermetallic compounds play an important role through diffusion reinforcement effects. As a mechanical buffer layer, the crack extension resistance of the plated layer is significantly improved, which is fundamentally different from the pure temperature-driven diffusion process. Not only is there isostatic stress as the driving force for material transport, but the regulation of crystal defect trajectories is even more critical. The elemental distribution state and phase structure characteristics are precisely controlled in the interface region, and this control effect is verified by experimental data.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results of EDS microzone analysis of the plated layer after hot isostatic pressing treatment at 1150\u0026deg;C/150 MPa are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. Three typical areas with gradient distribution characteristics in this plating system are selected for elemental quantitative analysis. Located at the outermost part of the plating layer is point 1 area, which is characterized by the enrichment of Cr element, where the atomic content ratio of Cr to Fe is close to 3:1. This area carries the main responsibility of corrosion protection function, and the high Cr ratio is in line with the expected compositional requirements of the plating layer design. Deeper into the bonding interface (point 2 area) from the plating layer to the substrate direction, the Cr/Fe atomic ratio gradually decreases to about 1.2:1, compared with the aforementioned outer area where the Cr content is significantly attenuated. Examples show that the formation of this composition gradient is closely related to the diffusion of cross-interface atoms during the hot isostatic pressing process, and the mechanistic explanation is attributed to the fact that in the high-temperature and high-pressure coupling field, the Cr atoms in the plating layer obtain sufficient activation energy and overcome the interfacial energy barrier to migrate to the substrate side, and at the same time the Fe atoms in the substrate diffuse in the reverse direction, and the transitional metallurgical bonding zone is generated by the composition. In this case, the ratio of Cr to Fe content tends to be 1:1, revealing that the interface initially realizes the atomic scale interdiffusion layer, which provides compositional conditions for the generation of stable intermetallic compounds. If the heat-affected zone of the substrate (i.e., point 3 region) is further explored, the Cr/Fe atomic ratio decreases to 1:4, while the Cr element still maintains a high level of 18.0%. This phenomenon reveals a unique feature of the enhanced diffusion mechanism of the hot isostatic process: the synergistic effect of the pressure gradient and the chemical potential gradient in the high-pressure, which results in the directional migration of Cr atoms obtaining an extra drive to increase the net flux, thus retaining a stable intermetallic layer far away from the interface in the substrate region. The matrix region away from the interface retains a robust Cr elemental reservoir. This compositional modulation induced by thermal isostatic pressure operation builds up a gradient interfacial layer of continuous compositional transition between the plating layer and the substrate, where the Cr concentration gradually decays with the enhancement of the distance from the interface from the outer high-Cr plating layer, to the interfacial interdiffusion reaction layer, and to the Cr penetration zone in the heat-affected zone of the substrate. At the same time, the mobilization of atomic migration under high pressure not only strengthens the interfacial bonding strength, but also stabilizes the expansion of intermetallic compounds and optimizes the stability of the interfacial structure of the plating system. In the heat-affected zone Cr non-equilibrium state aggregation, coinciding with the pressure-induced expansion plus high-temperature activation of the mobilization of the parallel implementation of the role of the common influx of so, this cross-scale component manipulation mechanism, the experimental construction of the bonding performance of the plating layer to provide support for the theory of the supply and practical verification of the effect.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Microhardness\u003c/h2\u003e \u003cp\u003eMicrohardness distribution characteristics in different post-treatment process conditions SLM molding 18Ni300 surface plating plating layer, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. 223.3 HV\u003csub\u003e0.2\u003c/sub\u003e \u0026plusmn; 10% for the original SLM molding substrate exhibits the average hardness value, additive manufacturing process in the formation of substable tissue structure and the existence of residual stress state, this phenomenon is in line with it. When the surface plating of pure chromium plating is implemented, the average hardness of the plated specimens is increased to 350.0 HV\u003csub\u003e0.2\u003c/sub\u003e\u0026plusmn;10%, and the hard-phase strengthening effect of the plating itself is thus manifested. Gradient distribution characteristics are significantly presented in the hardness of the plating, after 600 ℃ / 70MPa hot isostatic pressing treatment, the peak near the interface bonding appeared in the hardness test results, along the direction of the outer layer of the plating gradual attenuation of the hardness change trend. The occurrence of interfacial metallurgical reactions during hot isostatic pressing is closely related to this phenomenon: selective activation occurs in the atomic diffusion process between the plating layer and the substrate at medium temperature and high pressure, and the formation of the compositional transition zone originates from the migration of Cr atoms to the substrate side in conjunction with the reverse diffusion of Fe atoms. The orderly precipitation of stable intermetallic compounds is promoted, and the diffuse distribution of these hard phases at grain boundaries and dislocations effectively hinders the dislocation motion, resulting in an increase in local hardness. The increase in material densities occurs simultaneously with the significant compaction of holes and microcracks within the tissue under high pressure, and the reduction of indentation size effects in the hardness test is indirectly manifested in the enhancement of the macrohardness. When the hot isostatic pressing process parameters were increased to 1150\u0026deg;C/150 MPa, even better hardness properties were demonstrated in the coating system, with a maximum hardness value of 673.1 HV\u003csub\u003e0.2\u003c/sub\u003e \u0026plusmn; 10%. The overall hardness range of 406.3-673.1 HV\u003csub\u003e0.2\u003c/sub\u003e \u0026plusmn; 10% was significantly higher than that of the other process groups. The cross-scale interfacial modulation under the synergistic effect of high temperature and high pressure is the source of this strengthening effect: sufficient activation energy for atomic migration is provided at high temperatures, and the significant increase in the depth and extent of the interdiffusion of Cr and Fe atoms results in the formation of eutectic reaction layers of greater thickness at the interface. A significant increase in the volume fraction of nanoscale intermetallic compounds is seen in this process. The formation of fine-grained reinforced structures is promoted by the high-pressure environment while the abnormal grain growth is suppressed. The reduction of crystal defect density leads to the enhancement of lattice distortion, which results in the increase of plastic deformation resistance of the material. 1150℃/150MPa process of the plating-substrate interface mechanical bonding to the metallurgical bonding occurs, hot isostatic pressure-induced interfacial reaction mechanism of reinforcement not only to improve the overall hardness of the plating layer, the gradient hardness distribution of the design of the composite system to optimize the load-bearing capacity and fatigue resistance. Optimization.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Analysis and Discussion\u003c/h2\u003e \u003cp\u003eIn the context of contemporary materials processing, the development of selective laser melting technology has led to revolutionary changes in the field of preparation processes. A typical example is the 18Ni300 martensitic aging steel, where a special preparation process leads to a surface chromium electrodeposition behavior that is significantly different from that of conventional forming substrates. In contrast to the homogeneous equiaxial crystalline organization of forged or cast 18Ni300, the 18Ni300 substrate manufactured using the SLM process forms a multi-scale microstructure including cellular dendritic crystals, substable phases, and subgranular grain boundaries under rapid solidification conditions. The existence of microstructural variability has a decisive influence on the distribution of surface dislocations and the degree of chemical activity. The SLM18Ni300 surface, which exhibits a high-density dislocation network and activated chemical state, provides a rich cluster of high-energy sites for the chromium electrochemical deposition process, and chromium atoms can be seen to preferentially nucleate in these high-energy regions. On the contrary, the homogeneous equiaxial crystal structure of the conventional molding 18Ni300 material maintains the dislocation density at a low level, and the chemical activity is stabilized, which shows that the chromium nucleation sites are not only limited in number but also uniformly distributed, and the nucleation process is mainly governed by the conventional electrochemical driving force mechanism. The layerwise thermal gradient effect strongly influences the characteristics of the residual stress distribution within the SLM18Ni300 material. The generation of localized strain fields is thus triggered, showing a non-uniform state in the internal regions of the material. It is due to this strain field that the kinetic behavior of ion adsorption changes during the electrodeposition process. The surface ion adsorption process and migration paths are shifted in favor of the Cr ions to reach the suitable deposition sites more rapidly. This shows that the coating growth process is significantly regulated. In the 18Ni300 alloy prepared by the conventional molding process, there is no such local strain field induced by the layerwise thermal gradient. Ion migration following the conventional electrochemical adsorption mechanism is observed in these materials, and the surface deposition process is relatively smooth. The Cr deposition behavior present on the surface of conventionally molded 18Ni300 alloys with greater difficulty in initiation is observed, attributed to the lackluster characteristics of the nanoscale catalyst. Significantly higher values of critical overpotential were observed for this process. In sharp contrast to conventional materials, the high surface roughness characteristic of SLM18Ni300 poses a clear challenge to the chromium electroplating process. Pore formation tends to occur on rough surfaces, and examples show that this can further lead to coating delamination. The optimization of pre-plating processes, such as electrolytic polishing and pulsed laser remelting, is therefore of particular importance, as the application of these techniques results in a significant improvement of the surface roughness and mitigates the negative effects of porosity. Conventional molding 18Ni300 usually shows a low surface roughness index value, and its dependence on the pre-plating treatment is relatively weak.\u003c/p\u003e \u003cp\u003eHot isostatic pressing technology for SLM18Ni300 martensitic aging steel chrome plating layer shows a unique effect, compared with the traditional heat treatment process 18Ni300 chrome plating layer of the case, there are significant differences in the molding characteristics and performance enhancement dimensions. The hot isostatic pressing process, which lasts for 3 hours at a high temperature of 1150\u0026deg;C and a high pressure of 150 MPa, fundamentally realizes the reconstructive transformation of the chromium-plated SLM18Ni300 substrate-layer interface. The induction of microstructure homogenization and the activation effect of intermetallic phase formation work together to make the hardness of the plated layer break through the limiting value of the traditional electroplating process. The inter-element diffusion phenomenon is enhanced by HIP induction, and the two synergistic pathways strongly promote the nucleation process of Cr-Fe intermetallic phase. As a result, the atomic mobility is greatly enhanced by HIP, and the diffusion of Fe atoms from the base alloy to the plated layer is significantly accelerated, an accelerating effect that is difficult to achieve in conventional heat treatments. Due to the limitation of temperature and pressure conditions, the enhancement of atomic mobility in the traditional heat treatment process is limited, and the slowing down of Fe atom diffusion rate is obvious, which is not conducive to the rapid formation of intermetallic phase. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows the schematic principle of 18Ni300 chromium plating before and after different treatments. The FeCr intermetallic compound-rich bonding zone is formed in the HIP-treated sample, and its measured Vickers hardness value reaches 673.1HV0.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10%, which is upgraded by 90\u0026ndash;95% compared with the untreated sample. At the same time, the original dendritic structure of SLM was transformed by HIP treatment, and an isometric crystal structure with twinned grain boundaries was generated. This transformation of grain boundary structure is of great value significance, providing a low-energy channelization path for Cr atom migration [\u003cspan additionalcitationids=\"CR50 CR51\" citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. The grain boundary structure of 18Ni300 during conventional heat treatment produces a certain degree of change, but it is not able to form the ideal structural characteristics that are favorable for chromium atom migration and plating growth as in the case of HIP treatment. Residual compressive stresses are generated and play a key role in the HIP process. The dislocation-assisted Cr/Fe interdiffusion process is significantly facilitated by this stress. In contrast, the stress state generated by conventional heat treatment is complex and difficult to be precisely regulated, and it is not possible to form a stable stress environment that promotes the formation of intermetallic phases. This shows that the formation of substable Cr-Fe compounds in the 18Ni300 chromium plating layer after conventional heat treatment is difficult and the number of phenomena is small. The mechanism of the influence of hot isostatic pressing on the formation of SLM18Ni300 chromium electroplated coatings is fundamentally different from that of conventional heat treatment. These differences make the HIP-treated SLM18Ni300 chrome plating show significant performance advantages.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study focuses on the post-treatment strengthening effect of electrochromium plating coatings on the surface of additively fabricated 18Ni300 alloy, revealing the mechanisms by which different processes affect the microstructure and properties of the coatings. Transverse crack networking and delamination phenomena were observed in the tissue evolution of the coatings after heat treatment, while a flatter electrochromium plating and substrate bonding state appeared after hot isostatic pressing treatment.\u003c/p\u003e \u003cp\u003e(1) The synergistic effect of solidification defects during the additive manufacturing process caused a lack of surface integrity of the substrate.223.3 HV\u003csub\u003e0.2\u003c/sub\u003e\u0026plusmn;10% is the average hardness value of the SLM molded substrate. There is a deterioration in the flatness and roughness of the pure chromium plating without post-treatment.The Fe-Ni phase, FeNiCr phase, and the residual phase of monomeric Cr that is not involved in the reaction constitute its main phase composition, and the lack of thermodynamic activity of the system leads to the problem of incomplete elemental reaction.\u003c/p\u003e \u003cp\u003e(2)The plated layer shows complex microstructure responsiveness after heat treatment, presenting transverse crack network and delamination phenomenon.600℃/70MPa hot isostatic pressure treatment can make the surface of the plated layer flatter and the interface straightness can be maintained, but more holes are still present in the interior, and the densification needs to be further improved. The physical phase of the plated layer was transformed into Fe-Ni/Fe-Cr/Fe-Ni-Cr alloy phase and monolithic Fe/Ni/Cr mixed state.\u003c/p\u003e \u003cp\u003e(3) Significantly optimized plating properties were achieved by the 1150\u0026deg;C/150MPa hot isostatic pressing process: maintaining good surface flatness was achieved, and the formation of a dense and flat bonding interface with the substrate was possible. The hardness range is increased to 406.3-673.1HV\u003csub\u003e0.2\u003c/sub\u003e\u0026plusmn;10%, with a maximum hardness value of 673.1HV\u003csub\u003e0.2\u003c/sub\u003e\u0026plusmn;10% outperforming the other treatment groups, and the monolithic phase of the plating disappears completely. Assume the main corrosion protection function of the outer Cr element-enriched area of Cr/Fe atomic ratio of 3:1, down to 1.2:1 at the bonding interface Cr/Fe ratio shows that the example shows that the interface area atomic scale interdiffusion has been realized.\u003c/p\u003e \u003cp\u003eThe implementation of the hot isostatic pressing treatment technique has significantly improved the modulation of the atomic diffusion behavior at the interface between the plating and the substrate. The strengthening of the metallurgical bonding state is clearly visible, and the phenomenon of crack formation is significantly suppressed. The trend of hardness index enhancement was confirmed by experimental data.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe author thanks the financial support provided by the Jiangxi Key Laboratory of Green General Aviation Power (GrantNo. Ef202480368).\u003c/p\u003e \u003cp\u003eCorresponding author: Yong Li, E-mail:[email protected]\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eWei Xu , Xiangli Liu and Yong Li wrote the main manuscript text and Guoyang Zhao，Gaojian You prepared the funding. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data supporting the research in this paper are available in the main text and Supplementary Information.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMei, L. et al. 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Charact.\u003c/em\u003e \u003cb\u003e196\u003c/b\u003e, 112596. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matchar.2022.112596\u003c/span\u003e\u003cspan address=\"10.1016/j.matchar.2022.112596\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Additive manufacturing, Post-treatment of electroplating, Hot isostatic pressing","lastPublishedDoi":"10.21203/rs.3.rs-6815548/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6815548/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHot isostatic pressing (HIP) is widely used to enhance the intrinsic properties of additively manufactured 18Ni300 martensitic aging steel, which can eliminate internal defects and optimize the microstructure of additively manufactured metals. However, there is still a lack of systematic knowledge about the influence of hot isostatic pressing on the interfacial properties of chromium plating on its surface, which makes it difficult to provide a reliable theoretical basis and process guidance for the precise optimization of plating properties under complex working conditions. In order to solve the above needs and technical problems, this paper centers on the post-treatment strengthening effect of chromium plating on the surface of additively manufactured 18Ni300 alloy to carry out in-depth investigation. Without post-treatment of pure chromium plating layer flatness and roughness degradation phenomenon obviously exists, through the XRD analysis to confirm that the composition of its physical phase contains Fe-Ni phase, FeNiCr phase and monolithic Cr residual phase. The microstructure response of chromium plating layer after heat treatment shows complex characteristics, transverse crack network and delamination phenomenon is triggered by the internal stress relaxation and crystal structure reconstruction of the plating layer. 600℃/70MPa hot isostatic pressing conditions, the plating layer surface flatness and interfacial straightness can be maintained, but there are still many internal pores, and densification needs to be improved. 1150℃/150MPa hot isostatic pressing process has a significant effect on the optimization of the performance of the layer: the surface flatness and interface straightening can be maintained, and the internal porosity still has more holes, and densification should be improved. The optimization effect is obvious: the surface flatness is well maintained; the interface with the substrate is formed; the hardness is greatly increased to 406.3-673.1HV0.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10%, and the monolithic phase disappears completely. The effective modulation of the atomic diffusion behavior at the plating-substrate interface by the hot isostatic pressing treatment was confirmed by the study: metallurgical bonding was strengthened; crack formation was suppressed; and the hardness and corrosion resistance were significantly improved. The results of the study open up an important new technological path for the optimization of surface protective layers of additively manufactured alloys.\u003c/p\u003e","manuscriptTitle":"Influence of post-treatment on the performance of SLM forming 18ni300 electroplated coatings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-20 15:59:45","doi":"10.21203/rs.3.rs-6815548/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8192334f-075f-4401-bc50-690e137a25e4","owner":[],"postedDate":"June 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":50251166,"name":"Physical sciences/Physics/Condensed matter physics"},{"id":50251167,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2025-08-12T05:38:20+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-20 15:59:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6815548","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6815548","identity":"rs-6815548","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}