The manufacture of metallic components involves alloy design, raw material preparation, melting, ingot/slab casting, hot forging or rolling, heat treatment, and precision cold processing etc. Consequently, research on the entire life cycle of metal production and application is imperative. Only by integrating the complete life cycle of the technological chain can the properties of metals be fully and appropriately utilized. Previous research has primarily focused on breakthroughs at individual “points”, often neglecting the “chain”. This has led to a “chain break” phenomenon in the processing of metal materials and components, resulting in high-end components that are unqualified, unstable, unreliable, or heavily dependent on imports. To address these issues, this study takes the research on the 8-meter-diameter main bearing of a shield tunneling machine as an example. It adopts novel V, B, and rare earth co-alloying in bearing steel for bearing rings, leveraging high-purity and high-homogeneity bearing steel production, as well as precision machining of high-performance bearing components. The study elucidates key technologies and their correlations throughout the bearing manufacturing process, with a particular focus on heat treatment technology that linking bearing materials to components and precision machining technology for large rollers. Through the development of whole-chain technologies, the main bearing for the shield tunneling machine was successfully manufactured. Building upon this research, a new concept of metal chain creation is proposed. This concept begins with alloy design and connects the entire chain of raw material preparation, melting, ingot/slab casting, hot forging or rolling, heat treatment, and precision cold processing, assembly manufacturing, evaluation, and application test. By identifying and manipulating critical data at each stage of the process, iterative optimization is achieved. This approach integrates the technological chain, fosters an innovation chain, connects the industrial chain, and realizes controllable manufacturing of metal materials and high-end components.

Mg/Mg bimetallic components, especially Mg-Al-Si/Mg-Gd-Y-Zn bimetals, hold promise for applications in the aerospace and automotive industries as structural materials because of their potential advantages of low cost, lightweight, high strength, and high plasticity. At present, Mg/Mg bimetallic components are primarily fabricated via extrusion and compound casting. However, these conventional processes are complex and have low forming efficiency. Recently, rapid advancements in additive manufacturing have enabled the real-time manufacturing of bimetallic structural components. In particular, wire arc additive manufacturing (WAAM) offers technical advantages for improving the forming efficiency of large-sized bimetallic components. Herein, to enhance the forming efficiency and interfacial performance of large-sized Mg/Mg bimetallic components, a thin-walled Mg-Al-Si/Mg-Gd-Y-Zn bimetallic component was fabricated using WAAM technology. Specifically, a Mg-Al-Si alloy thin wall was first deposited and then cooled to room temperature over a period of time. Subsequently, the top layer of the Mg-Al-Si alloy thin wall was remelted, followed by the deposition of the Mg-Gd-Y-Zn alloy. Further, the macroscopic morphology, microstructure, microhardness, and mechanical properties of the bimetallic component were examined. Based on the macroscopic morphology, bimetallic components exhibited good interface bonding through WAAM. OM images demonstrated a transition zone near the bimetallic interface with a thickness of approximately 1.4 mm. The line scanning results and EPMA mappings revealed the formation of a composition gradient in the transition zone due to element diffusion. From the Mg-Al-Si alloy side to the Mg-Gd-Y-Zn alloy side, the Al and Si contents gradually decreased, while the Gd, Y, and Zn contents gradually increased. Based on the nonequilibrium solidification phase diagram and microstructure analysis, the bimetallic component comprised three regions: the Mg-Al-Si region with the Chinese-script Mg₂Si phase; transition region comprising granular Mg₂Si, the Mg₃(Gd, Y) phase, and the Mg₅(Gd, Y) phase; and Mg-Gd-Y-Zn alloy region with the Mg₁₂Zn(Gd, Y) phase as the primary component. After microhardness testing, the hardness of the bimetallic component continuously increased from 57 HV_0.5 (Mg-Al-Si alloy side) to 90 HV_0.5 (Mg-Gd-Y-Zn alloy side) due to the composition gradient and small second phases in the transition zone. The results of tensile testing at room temperature (20 ^oC) showed that the strength of the bimetallic component was close to that of the Mg-Al-Si alloy, with an ultimate tensile strength of 236.8 MPa and a yield strength of 102.2 MPa. Meanwhile, the elongation and hardening index of the bimetallic component were close to those of the Mg-Gd-Y-Zn alloy, reaching 11.0% and 0.323, respectively. The fracture position of the WAAM Mg-Al-Si/Mg-Gd-Y-Zn bimetal was located in the transition zone. The fracture mechanism of the Mg-Al-Si alloy was primarily ductile, while those of the bimetal and Mg-Gd-Y-Zn alloy were quasi-cleavage.

Ni-based superalloys have shown great application potential as component materials in aircraft engines because of their excellent mechanical properties at high temperatures. With the development of engine and power plant boiler tubes, the high-temperature creep resistance of nickel-based superalloys has become an important indicator for evaluating the mechanical properties of superalloys. In this study, the creep behavior of the as-cast Ni-based superalloy with the coprecipitation of γ′ and γ″ phases at 750 ^oC and 120 MPa was investigated. The results show that the creep deformation behavior and creep property change with the size of the γ'/γ'' phases. A number of dislocations are cut into the γ'/γ'' phases, forming continuous stacking faults in the γ channel and γ'/γ'' phases when a high amount of compact γ'/γ'' phases are precipitated, leading a inferior creep property. Increasing the size of the γ'/γ'' phases, the dislocations are easily cut in the γ′ phase and isolated stacking faults are formed in the γ′ phase, which significantly enhances the creep property. Further increasing the size of the γ′ phase, the dislocations are piled up on the interface of the γ/γ′ phases, and the γ′ phase is looped with dislocations, which decreases the creep property. Given the precipitation of the deleterious Laves phases, the grain boundaries (GBs) are weakened. However, the stretch of cracks is restrained, and the creep properties of the alloy are enhanced because of the moderate needle-like η/δ phases in the GBs. The precipitation of the overdose η/δ phases provides a favorable location for crack nucleation and accelerates alloy failure.

FGH96 alloy is a nickel-based superalloy that is commonly used in fabricating the turbine disks of aero engines owing of its excellent mechanical properties. Because the properties of nickel-based superalloys are determined based on their microstructure, researchers have been studying the evolution of microstructure in FGH96. However, most studies have focused on FGH96 superalloys that have undergone a hot isostatic pressing (HIP) process or a combination of HIP and hot isostatic forging. Recently, hot extrusion (HEX) has been widely used for manufacturing FGH96 superalloys; however, the research on alloys manufactured via HEX is scarce. In this study, FGH96 superalloys were solution heat-treated at temperatures ranging from 1100 ^oC to 1260 ^oC, and the evolution of their microstructure was analyzed via OM, EBSD, and TEM techniques. The mechanism of static recrystallization and the formation mechanism of Σ3 twin boundaries were also investigated. The results showed that the static recrystallization grain size and grain boundaries, including small angle boundaries, large angle boundaries, and Σ3 twin boundaries, were substantially influenced by the solution temperature. Furthermore, a distinct correlation existed between the microstructure evolution and solution temperature. The static recrystallization in the FGH96 alloy mainly occurs through the nucleation and growth of subgrains at temperatures ranging from 1100 ^oC to 1260 ^oC. During the static recrystallization process, a large number of stacking faults formed at the (\mathrm{11}\overline{\mathrm{1}}) close-packed plane, which improved the free energy. Therefore, to reduce the free energy, subsequent atoms were stacked symmetrically to the stacking faults, leading to the formation of Σ3 twin boundaries.

Ti and titanium alloys are preferred for cryogenic applications, particularly at a liquid hydrogen temperature of 20 K, in aerospace due to their high specific strength, good corrosion resistance, low magnetic permeability, and low thermal expansion coefficient. Currently, the most common cryogenic titanium alloys are extra-low interstitial α-type and near α-type alloys. However, they exhibit inadequate age hardening and low cold-forming ability. Furthermore, they do not meet the enhanced strength-ductility requirements for cryogenic structural components. Metastable β-type titanium alloys with a {332}<113> twinning-induced plasticity (TWIP) effect have shown enhanced mechanical properties, such as a favorable balance of strength-ductility at ambient and cryogenic temperatures. Therefore, they are considered promising titanium alloy candidates for cryogenic applications. The content of interstitial elements, particularly the O content, has a substantial impact on the cryogenic ductility of titanium alloys. Therefore, all cryogenic titanium alloys have extremely rigorous requirements regarding the O content. However, the effect of O content on the cryogenic tensile behavior of {332}<113> TWIP alloys remains unclear. This study investigated the cryogenic tensile behavior of Ti-15Mo alloy with O contents of 0.2% and 0.4% (mass fraction, the same below) at 20 K. The tests were conducted using HRTEM, FIB, EBSD, SEM, OM, and a tensile testing machine fitted with a cryogenic system. Results show that the alloy comprising 0.2%O content (0.2O alloy) exhibits a good combination of tensile strength (1825 MPa) and elongation (7.5%). This alloy displays typical microvoid coalescence fracture characteristics. Alternatively, the alloy with 0.4%O content (0.4O alloy) presents a high tensile strength of 1973 MPa, a relatively low elongation of 1.5%, and typical cleavage fracture characteristics. The discrepancy in cryogenic tensile properties between the two alloys can be attributed to the effect of O content on the formation of {332}<113> twins. Several {332}<113> twins appear in the 0.2O alloy, whereas only a small number of twins are observed near the fracture region in the 0.4O alloy. The exceptional strength of the 0.2O alloy is attributed to the enhanced critically resolved shear stress of twinning, while the impressive elongation is attributed to the formation of numerous twins that impede local plastic deformation. The 0.2O alloy exhibits a noticeably serrated tensile curve and multiple necking. The activation of twins in the necking region hinders local plastic deformation and necking, thus enhancing the strength-ductility combination. Hence, by effectively using the interstitial element O, the cryogenic mechanical properties of metastable β-type titanium alloys can be effectively tailored as per requirements.

A shrouded impeller is an essential component of a liquid rocket, mainly responsible for transporting and pressurizing liquid fuel or oxidant. Owing to the low temperature and high-rotation speed of the working environment, materials with high performance are required for fabricating the impeller. With its excellent low temperature mechanical properties and high specific strength, Ti-5Al-2.5Sn extra-low interstitial (ELI) alloy has been widely applied in fabricating liquid rocket components, including the shrouded impeller. Considering the geometric complexity of the impeller, the powder metallurgy-hot isostatic pressing (PM-HIP) route is a suitable method for impeller formation. PM-HIP technology has a similar forming capability as precision casting but avoids casting defects, realizing the parts with reliable service performance. However, the mechanical properties and dimensional accuracy of the impeller may be influenced by the variation of powder particle sizes. Herein, three kinds of Ti-5Al-2.5Sn ELI prealloyed powders with different particle size distributions (average particle size D₅₀ = 125, 94, and 73 μm) were prepared by adjusting the process parameters of gas atomization and screen meshes. Then, their corresponding shrouded impellers were manufactured via the PM-HIP route at 940 ^oC, 120 MPa for 3 h. Subsequently, the impellers were annealed at 815 ^oC for 1.5 h, followed by air cooling. The effect of powder particle sizes on the mechanical properties of shrouded impellers was analyzed using cryogenic-temperature tensile tests. The porosity defect of impeller slices was detected using industrial computed tomography. The microstructure of the impellers was characterized using SEM and TEM. Meanwhile, the mechanism of low temperature deformation was also discussed. All three impellers exhibited homogeneous microstructure with fine grains, and their mechanical properties were comparable to the level of wrought alloys; specifically, the tensile strength was about 1300 MPa, and the elongation was 20% at 77 K. In addition, many twins were found in the deformation zones, including the types of {\mathrm{10}\overline{\mathrm{1}}\mathrm{2}}, {\mathrm{10}\overline{\mathrm{1}}\mathrm{1}}, and {\mathrm{11}\overline{\mathrm{2}}\mathrm{2}}. PM-HIP impeller size was calculated using the finite element method in the modified Gurson model and compared with the size of the actual impeller. Dimensional shrinkage was consistent between the finite element simulation result and the actual part, and the deviation in the flow channel was < 0.3 mm.

The initial lamellar microstructure of titanium alloys significantly affects their microstructural evolution and mechanical property during thermo-mechanical treatments. Thus, the evolution of the initial lamellar microstructure must be explored to control the microstructure and enhance the mechanical property. The present work focuses on the evolution of the lamellar microstructure during β→α phase transformation via interrupted furnace cooling experiments to analyze the growth behavior of the grain boundary α phase (α_GB) and its effect on the subsequent growth of intragranular α lamellae and microtexture. Results show that when titanium alloy furnace cools from the β phase field to the α + β phase field, the α_GB holding Burgers orientation relationship (BOR) with both sides of β grains (2-BOR α_GB) has an advantage for early transformation at the β grain boundary. In particular, type II (49.5°/<110>) and type III (60°/<110>) β grain boundaries are preferential sites for the early nucleation of α_GB particles. As the temperature decreases, α lamellae holding similar orientation to 2-BOR α_GB grow to both sides of β grains. Thus, 2-BOR α_GB and both sides of α lamellae form a strong microtexture at the grain boundary. At the early growth period of the α phase, the smaller the θ_2-BOR (misorientation of the close-oriented α_GB variant pair of parents β1 and β2) of 2-BOR α_GB, the earlier the formation of a strong microtexture at the grain boundary. 2-BOR α_GB preferentially precipitates, whereas the α_GB holding BOR with only one side of the β grain (1-BOR α_GB) nucleates. α lamellae holding a similar orientation to 1-BOR α_GB grow to one side of the BOR-β grain (holding BOR with α_GB), whereas α lamellae with a different orientation grow in the non-BOR-β grain. Thus, 1-BOR α_GB and one side of α lamellae form a weak microtexture at the grain boundary.

As the service environment changes, the widely used galvanized coating faces challenges due to its overly thick coating and insufficient corrosion resistance. Zn-2.0Al-1.5Mg coatings have emerged as an alternative to conventional galvanizing because of their excellent corrosion resistance and are extensively used in buildings, home appliances, and automobiles in harsh environments. The marine environment, known for its high corrosiveness, faces considerable material corrosion problems. Highly resistant materials, such as Zn-2.0Al-1.5Mg coating, stainless steel, have found applications in the marine environment. However, the development period of Zn-2.0Al-1.5Mg coating is short, and further research is required to determine its suitability for highly corrosive marine atmospheric environments. Consequently, the laboratory dry-wet alternating cycle corrosion test method, corrosion mass loss, SEM, XRD, EIS, and potentiodynamic polarization were used to investigate the corrosion behavior (e.g., corrosion kinetics, corrosion product evolution, corrosion morphology, and electrochemical behavior) of Zn-2.0Al-1.5Mg coatings in a simulated marine atmosphere. Results show that the initial corrosion product is ZnO at 168 h, with Zn₅(OH)₈Cl₂·H₂O appearing after 168 h of corrosion cycles (336, 504, 672, 840, and 1848 h). The emergence of ZnO at 168 h is attributed to the shortened dry-wet alternating cycle time, while that of Zn(OH)₂·0.5H₂O at 1848 h is attributed to the depletion of Mg or Al elements. The corrosion rate of Zn-2.0Al-1.5Mg coatings in the simulated marine atmosphere exhibited an M-shaped curve over time, closely related to the evolution of corrosion products. Between 0 and 840 h, the corrosion rate increased, except for a decrease between 336 and 504 h; this trend may be attributed to the disappearance of ZnO and an increase in the amount of Zn₅(OH)₈Cl₂·H₂O. Combined with the electrochemical results, it is speculated that the corrosion will accelerate with further exposure after 1848 h.

The lead-cooled fast reactor is considered one of the promising Generation IV nuclear energy systems. Structural materials used in the construction of pressure vessels and internals for this reactor include 300 series austenitic stainless steels. Nb-containing austenitic stainless steels are developed to improve corrosion properties, mechanical properties, and irradiation resistance. However, coarse primary NbC carbides are formed during solidification in these steels and cannot be eliminated through subsequent hot working and heat treatment. Recently, researchers have found different oxidation behaviors between secondary phase particles and the matrix, which affect the material's corrosion properties. However, the oxidation behaviors of primary NbC are rarely reported. This study analyzes the corrosion behaviors of a solution-treated Nb-containing austenitic stainless steel plate after exposure to oxygen-saturated liquid lead-bismuth eutectic (LBE) at 550 and 600 ^oC using SEM, EPMA, XRD, and TEM. The results show that the oxidation probability of NbC is correlated with its location in the samples at 550 ^oC. NbC at the initial surface is easily oxidized, while NbC within the interior is difficult to oxidize due to the low equilibrium oxygen partial pressure in the inner oxide layer, which suppresses the oxidation of NbC. However, NbC at the initial surface and within the interior are prone to be oxidized as the temperature increases to 600 ^oC. Compared to the matrix, NbC oxidizes into Nb₂O₅, resulting in a higher Pilling-Bedworth ratio (PBR). This leads to high compressive stress and resultant microcrack formation in the surrounding oxide layer. Additionally, the presence of CO₂ generated during the oxidation of NbC within the interior reduces the compactness of the oxide layer, leading to a higher growth rate.

The environment of the polar regions substantially differs from that at middle and low altitudes, resulting in the distinct degradation behavior of materials in these environments. Low alloy steels with high strength and good corrosion resistance are widely used as structural steels in engineering, but their corrosion behavior in the Antarctic atmosphere has been rarely reported. In the present work, an outdoor exposure experiment was conducted at the Zhongshan station, a research station located in Antarctica, to investigate the atmospheric corrosion behavior of Q460 and Q690 low alloy steels after 1 and 12 month exposures. The surface and cross-sectional morphologies were observed by SEM, and the phase composition of the rust layer was identified by XRD and Raman spectroscopy. The surface morphology and topography of the steel after removing the corrosion products were visualized by SEM and CLSM, respectively. The results show that the electrochemical corrosion process can occur beneath the snow and ice layer in the extremely low temperatures of the Antarctic environment. In the early stage of exposure, the freeze-thaw cycling of ice and snow leads to the development of a surface electrolyte film which persists for a long time, and this promotes corrosion reactions and accelerates localized corrosion. The corrosion rates of Q460 steel and Q690 steel were 29.7 and 77.0 μm/a, respectively, after a one-month exposure to the Antarctic environment. After 12 months of exposure, the corrosion rate decreased to 10.7 and 18.7 μm/a, respectively. The main corrosion products were goethite, lepidocrocite, akaganeite, and magnetite/maghemite. Over the short term, the ice and snow layer meant there were more chloride ions at the interface between the metal and the rust layer compared to warmer environments, and this resulted in more akaganeite forming within the rust layer as well as severe localized corrosion beneath the rust layer. Moreover, due to the freeze-thaw cycles of the surface ice and snow in the low temperature environment, more cracks were produced within the rust layer. After a longer period of exposure, the metal surface became covered with ice and snow. The ice and rust layer formed a barrier to dissolved oxygen and corrosive ions which inhibited the occurrence of further corrosion and resulted in a decrease in the corrosion rate and the evolution from localized corrosion to uniform corrosion.

With the promotion of the deep-sea strategy of China, the safety of metallic structural materials in deep sea is considered critical for development of deep-sea engineering equipment. High-strength low-alloy (HSLA) steel is widely used in pressure hulls of deep-sea submarines and oil platforms. However, HSLA steel is affected by the complex mechanical environment during its long-term service in the deep sea, leading to severe corrosion failure. Therefore, research on the effects of the hydrostatic pressure and tensile stress in deep sea on the stress corrosion behavior of HSLA steel is beneficial for the development, application, and lifetime prediction of deep-sea engineering equipment. Here, experiments were conducted using Ni-Cr-Mo-V steel, and the electrochemical measurement system and slow strain rate tensile (SSRT) test system in a simulated deep-sea environment were established in laboratory. The electric double-layer structure at the metal-solution interface was investigated using the differential capacitance curve, and the corrosion current density of the alloy was characterized with the linear polarization curve. The morphology of pits at local corrosion sites and fracture after the SSRT test were observed through SEM, and the size of the pits was analyzed using white-light interferometry. The stress corrosion cracking (SCC) sensitivity of the alloy was studied utilizing the SSRT test. The effects of the hydrostatic pressure and deformation on the concentration of H⁺ near the alloy surface were determined via the hydrolysis of metal cations. The results illustrated that the hydrostatic pressure can improve the SCC susceptibility of Ni-Cr-Mo-V steel in 3.5%NaCl solution, which can be affected by the dual effects of the interaction of the hydrostatic pressure and tensile stress on the local corrosion behavior. On the one hand, the interaction of the tensile stress and hydrostatic pressure affects the expansion and structure of pits and suppresses the adhesion of corrosion products to the alloy surface. On the other hand, the hydrostatic pressure and tensile stress affect the electric double layer at the metal-solution interface and subsequently promote the hydrolysis of metal cations, increasing the H⁺ concentration near the alloy surface. Additionally, the fracture mode of Ni-Cr-Mo-V steel in 3.5%NaCl solution is independent of the hydrostatic pressure; however, the hydrostatic pressure determines the shallow and small structure of the dimples in the fracture.

Adequate studies have not been conducted on the low cycle fatigue properties of oxide dispersion strengthened (ODS) steels that are typically used for fusion reactors worldwide. Moreover, the majority of the fatigue properties are examined with a small sample size due to the restricted manufacturing capacity, which is insufficient for determining the comprehensive properties of bulk materials. Research on the fatigue properties of Chinese ODS steels was conducted recently. However, it is quite uncommon to report the fatigue properties of self-produced 9Cr-ODS steel. Consequently, this work is the first to examine the effect of a cyclic strain on the low cycle fatigue behavior of a representative low-activation 9Cr-ODS martensitic steel. Hence, the strain control test method was employed here in a strain amplitude range of 0.3%-0.8% at room temperature. The cyclic stress response curves, hysteresis loops, relationships between strain amplitude and life, stress amplitude and plastic strain were obtained, and the corresponding fatigue parameters were summarized. Furthermore, the microstructural evolution, fatigue fracture morphology, and crack propagation characteristics during the fatigue process were analyzed. The results revealed that the cyclic stress response behavior of the 9Cr-ODS steel was related to the strain amplitude. With an increase in the strain amplitude, the peak stress in the tension zone of 9Cr-ODS steel increased and the fatigue life decreased. The relationship between cyclic strain and life agreed well with the Coffin-Manson model. Additionally, the 9Cr-ODS steel had no obvious cyclic hardening but revealed a cyclic softening under higher strain amplitudes of 0.5%-0.8%. The microstructure analysis showed that for higher cyclic strain amplitudes, the average grain size and the fraction of the large-angle grain boundaries increased gradually with a reduction in the dislocation density, leading to the cyclic softening of the material. The fatigue crack initiated at the surface and propagated inward by the transgranular mode. The fine grain boundaries and subgrain boundaries of the 9Cr-ODS steel could induce crack deflection, reduce crack propagation rate, and increase fatigue crack propagation life. Moreover, under the same strain amplitude, the peak stress in the tension zone of the steel was almost twice that of the China low activation martensitic (CLAM) steel without a reduction in the fatigue life, indicating a superior low cycle fatigue resistance of the 9Cr-ODS steel.

The composite rebar of stainless steel is used as a new type of structural material and can meet the strict performance requirements of marine service, effectively solving the overcapacity problem of basic materials. The quality of the composite interface generally depends on the interface microstructure and the distribution of interface compounds. However, the deformation parameters also indicate the interface quality, and a composite product with a uniform interface and excellent performance could be obtained by controlling the reduction rate. Herein, high-temperature compression experiments were conducted on the composite materials of 304/Q235. The near-interface characteristics of the microstructure evolution were studied under a strain rate of 1 s^-1 and reduction rates of 20%, 40%, and 60% to elucidate the dynamic nucleation mechanism and grain boundary migration of the stainless steel side of the interface. Based on Fick's second law of one-way flow under unsteady conditions, an element diffusion model of the composite interface transition region was established to explore the correlation between the interface microstructure evolution and element diffusion behavior. The results show that there is an uncoordinated dynamic recrystallization occured on both sides of the interface at the temperature of 1000 ^oC. The grains completely change during dynamic recrystallization at the carbon steel side of the interface, while the recrystallization dominated by the dislocation mechanism significantly occurs under the working condition with a high pressure rate (60%) at the stainless steel side. At a deformation temperature of 1100 ^oC, dynamic recrystallization is controlled by the dominant twinning mechanism at the stainless steel side, where Σ3 twinning accelerates the recrystallization process. At this time, the coordination of deformation is significantly improved on both sides of the interface. Further studies show that grain refinement and the movement of dislocation and twin defects have a positive effect on the element diffusion behavior. In addition, interfacial intermetallic compound evolution and cavity closure have a significant enhancement effect on interfacial elemental diffusion behavior. The Boltzmann-Matano method is employed to determine the position of the Matano surface, and the Levenberg-Marquardt method is employed to fit the multivariate nonlinear parameters. The established element diffusion model can accurately reflect the elemental concentration in the composite interface transition region, which provides theoretical support for the improvement of metallurgical bonding quality and interface performance control of composite materials.

Chemical boundaries (CBs) delineate two areas within a continuous lattice that have same structures but exhibit a sharp chemical discontinuity. CBs can be seen as a unique planar defect that is distinct in certain aspects from traditional physical interfaces such as phase boundaries and grain boundaries (GBs). Recently, GBs have been established within the austenite of medium Mn steels; they have been proven to substantially enhance the stability of austenite. This allows austenite to be easily retained at room temperature and offers additional possibilities for managing its mechanical stability. In this study, a crystal plasticity modeling was performed to simulate the deformation behavior of austenite containing a CB. First, an extended dislocation-based crystal plastic model that incorporates the deformation-induced martensitic transformation and stacking fault energy was developed. The inverse Nishiyama-Wassermann (N-W) relation was used to accurately describe the orientation relationship between austenite and newly formed martensite. The Mn content on both sides of the CB is taken as a state variable to calculate the stacking fault energy. This leads to varying responses in the deformation-induced martensitic transformation and dislocation slip within a single austenite grain. Results reveal a strain incompatibility between Mn-rich and Mn-poor austenite that causes a geometrically necessary dislocation to accumulate near the CB. Furthermore, the deformation-induced martensitic transformation on both sides of the CB behaves differently, leading to a “spectral” distribution of mechanical stability within a single austenite grain. This heterogeneity in the mechanical stability of austenite is highly beneficial. It allows a gradual deformation-induced phase transformation throughout the entire deformation process, which is crucial for enhancing the strength and plasticity of transformation induced plasticity (TRIP)-aided steels simultaneously.