The tensile and bending absorption energies, microstructural evolution, strain distribution, and crack behavior of U-notched samples of TRIP steel with multiscale retained austenite at different loading rates were investigated. For the tensile sample, it is demonstrated that the transformation amount of retained austenite to martensite before necking increases very slightly with decreasing loading rate. This provides a comparable transformation-induced plasticity effect, and thus leads to a similar absorption energy before necking at different loading rates. After necking, much retained austenite, especially at lower loading rates, has further transformed into martensite/austenite islands or martensite blocks, which provides a sustained high transformation-induced plasticity effect, and thus results in an increase in the absorption energy after necking and the total tensile absorption energy with decreasing loading rate. However, for the bending sample, much retained austenite in the high-strain region at U-notched bottom and crack tip, especially at lower loading rates, has transformed into martensite/austenite islands or martensite blocks, which provides a larger number of nucleation sites for crack initiation and paths for crack propagation, and thus decreases the crack initiation, crack propagation, and total bending absorption energies at lower loading rates.

A novel multiheterogeneous gradient structure was successfully fabricated in medium Mn steel via a hybrid process integrating low-temperature aging, cyclic torsion, and short-term high-temperature annealing. This structure exhibits distinct gradient distributions of austenite phase fraction and dislocation density along the macroscopic radial direction of the specimen. Microscopically, austenite grains within each gradient layer display diverse morphological characteristics and size distributions, while ferrite grains contain a high density of nanoscale B2 precipitates. This unique hierarchical architecture enables the sequential activation of the transformation-induced plasticity (TRIP) effect across the core-to-surface gradient layers over a wide strain range. The synergistic interplay of multiple deformation mechanisms, including continuous TRIP effect, sustained heterogeneous deformation-induced (HDI) strengthening, twinning-induced plasticity (TWIP) effect in the surface region, and precipitation strengthening, yields an exceptional strength-ductility synergy. Compared with its homogeneous counterpart, the multiheterogeneous gradient structure achieves a similar to 70% enhancement in yield strength and a similar to 26% increase in ultimate tensile strength, while retaining excellent ductility of similar to 41%. These findings provide a promising strategy for developing medium Mn steels with superior strength-ductility balance and offer valuable insights for the design of advanced structural materials in engineering applications.

This study takes temperature as the core variable and systematically investigates the end-face sliding wear behavior of Inconel 625 alloy across a broad temperature range of 300-700 °C, aiming to reveal the temperature-dependent evolution of wear mechanisms and the anomalous variation in cross-section hardness. The results show that the specific wear rate exhibits a non-monotonic temperature dependence, reaching a minimum of 0.97×10-5 mm3 at 600 °C. Notably, an anomalous hardness peak of 259.60 HV is observed at 500 °C, contradicting the well-established law of thermal softening, and originates from the combined strengthening effects of dynamic γ″ precipitation and dynamic strain aging. At 700 °C, the hardness drops to 168.47 HV due to transitioning from γ″ to δ and recovery. Based on systematic experiments across the wide temperature range, a three-stage wear mechanism framework for Inconel 625 is established: 300 °C (adhesive dominated), 400-500 °C (transition zone), 600-700 °C (glaze lubrication) . This framework provides a complete physical picture of the transition from mechanical dominated damage to dynamic balanced protection and further to glaze-assisted self lubrication. The findings offer new insights into the broad-temperature wear behavior of nickel-based superalloys and provide experimental guidance for temperature window optimization and life assessment of high-temperature moving components such as aero-engine seals.

Gadolinium (Gd) exhibits great potential for neutron shielding applications owing to its neutron cross-section approximately 60 times higher than that of boron (B). However its alloying application in Ni-based and Febased alloys is significantly limited by issues such as cracking during processing and formation of coarse secondary phase. In this study, GH3535 alloy and Gd-containing GH3535 alloy were fabricated via laser powder bed fusion (LPBF). The effects of Gd addition on the printability, microstructural evolution, and mechanical properties of the alloys were systematically investigated. The high hot-cracking susceptibility of Gd in Ni-based alloy welding is suppressed in the LPBF process with high cooling rate and small melt pool, enabling the fabrication of crack-free samples with a relative density above 99.9%. Regarding microstructural evolution, Gd addition transforms the original M2C carbides into fine Ni5Gd phases that are continuously distributed along grain boundaries and interdendritic regions. These continuously distributed Ni5Gd phases impede dislocation motion and induce strain concentration at grain boundaries. With the addition of 1 wt% Gd, the yield strength of the alloy is increased by approximately 170 MPa. This work provides new insights for the alloy design and processing of Gd-containing GH3535 alloy, as well as for future alloying strategies of Gd in Ni-based alloys.

TiAl-based alloys show great potential for aerospace and automotive applications but are limited by room-temperature brittleness and insufficient high-temperature strength. This study employs first-principles calculations to systematically investigate the effects of Ga doping at different sites (Ti substitution, Al substitution, and interstitial positions) on the structural, electronic, thermodynamic, and mechanical properties of gamma-TiAl alloys. Results reveal that Ti-site substitution induces in-plane lattice contraction with c-axis expansion, while interstitial doping causes significant volumetric expansion. Electronic structure analysis shows that interstitial doping increases the density of states near the Fermi level, enhancing electron mobility, whereas Ti-site substitution strengthens bonding through enhanced d-d orbital hybridization. Al-site substitution exhibits the lowest thermal expansion coefficient (18 % reduction at 300 K), improving dimensional stability, while Ti-site substitution displays higher work functions (4.05-4.15 eV), suggesting better corrosion resistance. Mechanical properties are optimized at 0.03 % Ga concentration, at which the elastic modulus peaks at 194.48 GPa and the Pugh ratio (B/ G = 1.75) indicates improved ductility. However, higher concentrations (>= 0.04 %) lead to hardness reduction and increased elastic anisotropy. This work provides theoretical insights for optimizing TiAl alloys through controlled Ga doping strategies.

Rolling contact fatigue (RCF) is a critical failure mode of bearings. In this study, the novel GCr15Si1MoNbV bearing steel was subjected to low-temperature salt-bath austempering, and the effects of phase transformation during austempering on microstructure, mechanical properties and RCF behavior were investigated experimentally using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and RCF testing. The specimen austempered at 190 degrees C for 10 h with a multiphase microstructure composed of nanobainite, martensite, and a high volume fraction of retained austenite exhibited exceptional performance. This kind of multiphase microstructure provided high surface hardness, excellent impact toughness, and a favorable residual stress gradient characterized by compressive stress at surface and tensile stress at subsurface, which collectively delayed crack initiation and propagation. As a result, the basic rating life (L10), the median life (L50), and the characteristic life (Vs) of the martensite-nanobainite-austenite 10 h specimen were 2-3 times to those of the martensite-dominated 2 h specimen, and 3-5 times to those of the nanobainite-dominated 48 h specimen. These findings indicate that the synergistic optimization of multiphase microstructure and residual stress gradient is the key mechanism for enhancing the RCF performance of bearing steels.

This study examines the evolution of microstructure, the metastability of retained austenite (RA), and the corresponding mechanical behavior exhibited by a nanostructured bainitic bearing steel subjected to prolonged austempering within a transformation stasis regime. The results indicate that following the completion of nanostructured bainitic formation at 300 °C for 3 h, a prolonged austempering time does not alter the microstructure, but reduces the dislocation density in BF while increasing the carbon content in RA. For the 4 h and 6 h specimens, a reduction in the overall RA mechanical stability is observed, accompanied by different transformation rates of stress-induced martensite during tensile deformation. This behavior is largely due to the weakened constraint effect of the BF matrix and the evolution of a carbon concentration gradient within the RA. During the transformation stasis, prolonged austempering elevates the yield strength while maintaining an unchanged ultimate tensile strength, albeit with a marginal reduction in microhardness. Relative to the baseline elongation recorded for the 3 h specimen, both the 4 h and 6 h specimens exhibit enhanced ductility, with the 4 h specimen yielding a peak value of 16.8%, which is 1.66 times that of the 3 h specimen. This improvement stems largely from the greater RA volume fraction that transforms into stress-induced martensite in the 4 h specimen, as well as its continuous and stable transformation rate during tensile deformation. Therefore, it can be concluded that an appropriately prolonged austempering time within nanostructured bainitic transformation stasis is essential for optimizing mechanical performance. This study provides a low-cost, energy-saving isothermal heat treatment technical scheme for mass industrial production of high-performance bearing steel.

Ga2O3 is a wide-bandgap semiconductor, which has five different phases. Among these phases, beta-Ga2O3 is the most stable one. It has many outstanding characteristics compared to other semiconductor materials. To investigate the influence of doping on its electronic and optical properties, and given the current scarcity of studies on the effects of Co single doping and Co-N co-doping on the optoelectronic properties of beta-Ga2O3, first-principles calculations were employed to investigate the effects of Co and N single doping, as well as Co-N co-doping on the optoelectronic properties of beta-Ga2O3. The geometric structure, electronic structure, and optical properties of the systems were calculated and analyzed. The results show that both Co single doping and Co-N co-doping models are thermodynamically stable structures. Electronic structure analysis reveals bandgap reduction in all doped systems relative to intrinsic beta-Ga2O3. Particularly, Co-N co-doping synergistically integrates the advantages of both Co and N single doping, achieving further bandgap narrowing beyond that attained by individual Co or N doping. Optical property calculations demonstrate that Co-N co-doping is capable of effectively facilitating the red shift in the optical absorption coefficient, exhibiting a larger optical absorption range and intensity. The research results can provide references for experimental researchers in designing beta-Ga2O3 with enhanced optical performance and developing efficient photocatalysts.

This paper analyzes the reasons for the occurrence of strand separation in bimetallic composite conductors during the extrusion process. The study employed equipment such as resistance furnaces, optical microscopes, and coordinate measuring machines. The study investigated the relationship between the degree of strand separation in bimetallic composite conductors and factors such as heating time (t), heating temperature (T), the protrusion length at both ends of the outer individual wires (L), and the diameter of the outer wires (D). Research indicates: during the extrusion process, the degree of strand separation in bimetallic composite conductors increases with higher T, longer t, and greater L within the heating tube, while it decreases with larger D. Meanwhile, the study identified the range of critical heating time (t0) and the range of critical aluminum beam thickness (h0). Through the principle of moment of inertia equivalence for bending resistance, this critical thickness corresponds to a critical outer wire diameter (D0). Beyond the critical heating time t0, the degree of strand separation shows an insignificant change; below the critical heating time t0, the degree of strand separation exhibits a linear increase with prolonged heating time. Wire diameters below the critical value D0 accelerate bimetallic strand separation. Additionally, this paper introduces a method that enables the continuous production of bimetallic composite conductors during the extrusion stage.

A new multi-scale gradient structure has been successfully fabricated in medium Mn steel via cyclic torsion and aging treatments. Within millimeter-sized specimens, this structure exhibits hierarchical gradient characteristics: at the nanoscale, it encompasses gradients of B₂ precipitates, while at the microscale, it comprises gradients of grain size and austenite content. The tailored gradient distribution of B2 particles induces localized variations in the stacking fault (SF) energy of austenite across distinct gradient layers. This, in turn, activates multiple deformation mechanisms, such as SF formation and the twinning-induced plasticity effect. Moreover, the multi-gradient structure facilitates cross-scale dynamic strain partitioning during plastic deformation, thereby triggering a continuous austenite-to-martensite phase transformation from the sample’s center to its surface. This unique structural evolution preserves the integrity of gradient layers under high-strain conditions, notably enhancing hetero-deformation-induced hardening. Compared with its annealed counterpart, the multi-scale gradient medium Mn steel exhibits remarkable improvements in mechanical properties: the yield strength and ultimate tensile strength are increased by 39

Yttrium hydride (YHx) has recently attracted considerable attention as a highly promising candidate for the development of compact reactors. This is primarily attributed to its exceptional thermal stability and superior hydrogen storage capacity, which are particularly advantageous under high-temperature conditions. YHx samples were fabricated by spark plasma sintering (SPS) with systematically varied process parameters. Results reveal that the microstructure of sintered YHx exhibits significant variations under different sintering processes. SPS process promotes the densification of sintered YHx monoliths, and the co-evolution of microstructure and grain growth behavior optimizes phonon transport pathways, thereby enhancing the thermal conductivity. The thermal conductivity of sintered YHx decreases with increasing temperature. Optimized under the conditions of 10 0 0 degrees C/65 MPa/5 min, the sintered YHx achieved a relative density of 99.14 % and hydrogen content of 1.91 wt.%, exhibiting a maximum thermal conductivity of 67.8 W/(m K) at 300 K. This study conducted an in-depth analysis of the mechanisms influencing thermal conductivity variations and established more comprehensive sintering process-microstructure-thermal conductivity relationships for YHx. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

This study examines the electrochemical behavior and slow strain rate tensile (SSRT) properties of 67Si2CrNiAlMnMoCu steel featuring a multiphase nanobainitic microstructure consisting of bainitic ferrite (BF), retained austenite (RA), and martensite (M). Electrochemical measurements reveal that both the corrosion tendency and dissolution rate decrease with extended austempering time, with the sample austempered at 220 °C for 21 h showing the lowest corrosion susceptibility. SSRT results indicate that specimens with a nearly fully bainitic microstructure exhibit increased strength sensitivity to stress corrosion. Notably, the specimen austempered at 240 °C for 9 h demonstrates excellent corrosion resistance while retaining favorable overall mechanical properties, exhibiting a tensile strength-based stress corrosion cracking sensitivity coefficient as low as 4.1%.

Stable service performance of spring steel under complex working conditions is essential, and under the synergistic effect of corrosive environment and stress, stress corrosion cracking is very likely to occur. Austempering can change the microstructure of spring steel and thereby improve its stress corrosion sensitivity. In this study, methods such as scanning electron microscopy and slow strain tensile tests were adopted to investigate the effects of different austempering temperatures on the microstructure and stress corrosion resistance of 52CrMoV4 spring steel. The results show that crack initiation during stress corrosion cracking in the test steel is mainly related to anodic dissolution. The coarsening of bainite laths and the increase in the area of martensite–austenite islands accelerate stress corrosion cracking once stress concentration occurs. The steel austempered at 310 °C has the best resistance to stress corrosion, with a stress corrosion sensitivity value of only 2.4%, which is much lower than those of specimens under traditional processes (15.5–23.7%).

Intermetallic compounds have attracted widespread attention in the field of materials science due to their unique physicochemical properties. This study systematically investigates the electronic structure, elastic properties, and thermodynamic characteristics of three intermetallic compounds—CaNi₂, MgNi₂, and CaMgNi₄—using first-principles methods to evaluate their potential applications in high-temperature structural materials, energy storage, and catalysis. The results indicate that all three materials exhibit negative formation energies, suggesting their spontaneous formation and good thermodynamic stability, with MgNi₂ having the lowest formation energy and thus the highest stability. Band structure and density of states analyses reveal the metallic nature of these compounds, with anisotropic conductivity in the order of MgNi₂ > CaMgNi₄ > CaNi₂. In terms of mechanical properties, all materials have GH/BH ratios greater than 1.075, indicating good ductility, with CaNi₂ exhibiting the best ductility and CaMgNi₄ the worst. MgNi₂ shows the highest anisotropy index, implying a higher likelihood of cracking under specific loading conditions. These findings fill the knowledge gap regarding the electronic, elastic, and thermodynamic properties of the Ca-Mg-Ni system and provide a theoretical foundation for designing novel high-performance materials for efficient batteries, catalysts, and high-temperature applications.

Intermetallic compounds have attracted widespread attention in the field of materials science due to their unique physicochemical properties. This study systematically investigates the electronic structure, elastic properties, and thermodynamic characteristics of three intermetallic compounds-CaNi2, MgNi2, and CaMgNi4-using firstprinciples methods to evaluate their potential applications in high-temperature structural materials, energy storage, and catalysis. The results indicate that all three materials exhibit negative formation energies, suggesting their spontaneous formation and good thermodynamic stability, with MgNi2 having the lowest formation energy and thus the highest stability. Band structure and density of states analyses reveal the metallic nature of these compounds, with anisotropic conductivity in the order of MgNi2 > CaMgNi4 > CaNi2. In terms of mechanical properties, all materials have GH/BH ratios greater than 1.075, indicating good ductility, with CaNi2 exhibiting the best ductility and CaMgNi4 the worst. MgNi2 shows the highest anisotropy index, implying a higher likelihood of cracking under specific loading conditions. These findings fill the knowledge gap regarding the electronic, elastic, and thermodynamic properties of the Ca-Mg-Ni system and provide a theoretical foundation for designing novel high-performance materials for efficient batteries, catalysts, and high-temperature applications.

PurposeDue to its high strength and low-alloy composition, 20MnTiB cold-heading steel is widely used in critical structural applications across sectors such as aerospace, marine engineering and nuclear power. This study systematically investigates the high-temperature tensile behavior and constitutive modeling of 20MnTiB cold-heading steel.Design/methodology/approachIsothermal tensile tests were conducted under various deformation conditions (temperatures from 1173 K to 1373 K and strain rates from 0.1 to 10 s-1) to evaluate the material's flow characteristics and fracture mechanisms. Microstructural analyses using optical and scanning electron microscopy revealed that high-temperature plastic deformation is primarily governed by dynamic recovery and work hardening, with localized necking and microvoid coalescence leading to ductile fracture. A strain-compensated Arrhenius-type constitutive model and a modified Johnson-Cook model were developed to accurately describe the material's thermal deformation behavior.FindingsComparative evaluation of the models demonstrated that the Arrhenius model achieved a correlation coefficient of R-2 = 0.995 and AARE = 2.99%, outperforming the modified Johnson-Cook model, which yielded R-2 = 0.983 and AARE = 5.49%. These results confirm that the strain-compensated Arrhenius model provides a more accurate and reliable prediction of the high-temperature tensile flow behavior of 20MnTiB steel.Originality/valueIn this study, isothermal tensile tests were performed under various deformation conditions to systematically examine the material's high-temperature tensile response. The underlying deformation mechanisms and fracture characteristics were thoroughly analyzed. These models' accuracy and predictive capabilities were validated through experimental data, demonstrating their potential for practical application.

This study investigates the effects of different low-temperature austempering temperature and time on the phase fraction, morphology, distribution of microstructures and mechanical properties in 67Si2CrNiAlMnMoCu steel. The results indicate that the specimen austempered at 200 degrees C exhibits the earliest transformation due to the preforming martensite acting as nucleation for bainitic transformation and the lath martensite disappears as the austempering temperature and time increasing. The M/A islands decrease slightly in size and exhibit markedly less surface relief when specimen austempered at 240 degrees C from 9 h to 21 h. In addition, the product of strength and ductility of austempered specimens are all higher than the oiled specimens, especially the specimen austempered at 200 degrees C for 21 h is similar to 1.5 times higher than the oiled one. The impact toughness of the specimen austempered at 240 degrees C for 21 h is nearly 12 times higher than that of austempered at 200 degrees C for 3h.

52CrMoV4 alloy spring steel has excellent mechanical properties and is widely used in the production of automobile suspension systems, spring sheets, torsion bars, and other parts. This paper improves the traditional oil quenching process. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Electron Backscattered Diffraction (EBSD), tensile testing, and other methods were used to experimentally study the effect of heat treatment process on the microstructure and mechanical properties of 52CrMoV4 alloy spring steel. The results showed that specimens treated with traditional oil quenching process have higher strength but poor impact toughness. The introduction of bainite into the microstructure was achieved via austempering at 300 degrees C followed by low-temperature tempering, leading to a 32.1 % enhancement in impact toughness while maintaining the strength level. Furthermore, we demonstrated that tempering can effectively improve the distribution of carbides in the microstructure and reduce its dislocation density. By reducing the formation of nucleation sites on cleavage planes of impact specimens, this process significantly enhances the impact toughness. By optimizing the bainite austempering process of 52CrMoV4 spring steel, it can achieve excellent comprehensive mechanical properties, especially impact toughness. Thus, it can reduce the risk of damage under the impact and ensure the safety of equipment and personnel.

Yttrium hydride (YHx) is a highly promising neutron moderator material for nuclear reactors, known for its exceptional thermal stability and high hydrogen content. This study investigated the sintering mechanism and microstructural evolution of YHx monoliths processed by spark plasma sintering (SPS), with the effects of temperature, duration, and pressure. The results indicate that the sintering process can be divided into five stages: formation of sintering necks, rapid densification, anti-densification, re- crystallization, and grain growth. The anti-densification behavior is attributed to hydrogen desorption, phase transformation-induced volumetric contraction, and vacancy coalescence from hydrogen migration, leaving residual pores and lattice defects. Furthermore, increasing the sintering temperature and duration promotes recrystallization and grain growth, whereas elevated pressure effectively suppresses grain boundary migration. This research establishes fundamental processing-structure correlations critical for optimizing YHx moderators in nuclear applications. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.