Acta Metallurgica Sinica-English Letters最新文献

How to describe the austenite reverse transformation (ART) has always been considered as a key problem of controlling microstructures and mechanical properties in high-strength steels. So far, numerous studies have been conducted, unfortunately, without fully considering diffusion of elements, interface migration, and interaction between trans-interface diffusion and interface migration, as well as synergy of thermodynamic and kinetic for interfacial migration. A more flexible modeling for the ART is herein developed using thermodynamic extremal principle, where the concept of trans-interface diffusion in two steps, i.e., from the parent phase to the interface and from the interface to the product phase, as well as the Gibbs energy balance approach, was introduced to predict the behavior of interface migration and element trans-interface diffusion within the migrating interface. Subsequently, the thermodynamic driving force ΔG and the effective kinetic energy barrier Q_eff for the ART were also analytically performed, as well as a unified expression for so-called generalized stability (GS). It is demonstrated that the higher driving force in the ART generally results in the increased yield strength, while the larger GS tends to yield improved uniform elongation, thus forming a correspondence between the thermo-kinetics trade-off and the strength-ductility trade-off. Applying a proposed criterion of high ΔG-high GS, the present model can be adopted to design the ART, which will produce the austenite microstructure with high strength and high plasticity, as evidenced by the current experiments.

This study analyzed through-thickness distribution of residual stress in a 106 mm ultra-thick TC4 titanium alloy electron beam welded (EBW) joint after post weld heat treatment (PWHT) using X-ray diffraction (XRD) and deep-hole drilling (DHD) methods, and investigated the microstructure and mechanical properties. During the PWHT at 600 °C, a phase transformation (β → α) occurred in the EBW joint and affected the residual stress distribution and mechanical properties. The surface residual stress was mainly compressive stress, while the internal residual stress was mainly tensile stress in the welded joint. For the as-welded joint, the absolute value of surface residual stress was higher than the absolute value of internal residual stress. After PWHT, the residual stress in the treated joint was substantially reduced compared to the as-welded joint, particularly the surface stress, which relieved from − 425 to − 90 MPa. However, the residual stress relief effect had minimal positive impact on the internal region at 600 °C. PWHT resulted in a shift of the joint fracture location from the fusion zone (FZ) to the base metal (BM), and therefore exerted no noticeable effect on the joint strength, but increased the joint elongation significantly. This study provides valuable insights into the regulation of residual stress distribution of ultra-thick titanium alloy plates.

Bending is a crucial deformation process in metal sheet forming. In this study, the microstructural evolution of a highly ductile Mg–Er–Zr alloy sheet was examined in various bending regions under different bending strains using electron backscatter diffraction and optical microscopy. The results show that the Mg–Er–Zr extruded sheet has excellent bending properties, with a failure bending strain of 39.3%, bending yield strength, and ultimate bending strength of 75.1 MPa and 250.5 MPa, respectively. The exceptional bending properties of the Mg–Er–Zr extruded sheets are primarily due to their fine grain size and the formation of rare-earth (RE) textures resulting from Er addition. Specifically, the in-grain misorientation axes (IGMA) and the twinning behaviors in various regions of the specimen during bending were thoroughly analyzed. Due to the polarity of the tensile twins and their low activation stress, a significant number of tensile twins are activated in the compression zone to regulate plastic deformation. The addition of Er weakens the basal texture of the sheet and reduces the critical resolved shear stress difference between non-basal slip and basal slip. Consequently, in the tensile zone, the basal and non-basal slips co-operate to coordinate the plastic deformation, effectively impeding crack initiation and propagation, and thereby enhancing the bending toughness of the Mg–Er–Zr sheet.

Thermoelectric materials possess tremendous potential in energy regeneration owing to their capacity to produce power directly from heat. SnTe, a lead-free compound, is a prospective thermoelectric material. However, because of its elevated thermal conductivity, the thermoelectric performance of undoped SnTe remains at a low level. In this work, we induce ternary compounds CuFeS₂ into the SnTe matrix by ball milling. We observe the decomposition of CuFeS₂, which decomposes into FeS, Cu₂S, and other binary compounds. These newly generated binary compounds form micropores and secondary phases in the matrix. Combined with the natural grain boundaries in the polycrystal, they form all-scale hierarchical structures within the material, resulting in reduced lattice thermal conductivity. Overall, the produced SnTe + 2 wt% CuFeS₂ composites show the peak dimensionless figure of merit (ZT) up to 0.33 at 673 K, an increase of ~ 100% compared to the undoped SnTe.

The effect of intermetallic particles on the corrosion of 6061 aluminum alloy and its coating used in semiconductor processing systems was systematically studied via liquid and gas experiments and micromorphology characterization. The results revealed that a huge difference of corrosion resistance between imported and domestic 6061 aluminum alloys in HCl solution and gas acid mist experiments mainly was attributed to the different size and amount of Al₁₅(Fe,Mn)₃Si₂. The corrosion resistance of domestic 6061 alloy in dry/wet semiconductor electronic special gas environments was worse than that of imported aluminum alloy, and there are great differences in the corrosion mechanism of 6061 alloy caused by the second phase in the two dry/wet environments. And the corrosion resistance of the hard anodized alumina film was closely related to the microscopic morphology of holes. The vertical and elongated α-Al₁₅(Mn,Fe)₃Si₂ phase was formed in the rolled aluminum alloy that has been rolled perpendicular to the surface of the substrate. Compared to the horizontal long hole, the longitudinal long holes generated by the vertical α-Al₁₅(Mn,Fe)₃Si₂ phase will enable the corrosive medium to reach the substrate rapidly, which significantly weakens the corrosion resistance of the hard anodized film.

The microstructural evolution and mechanical properties of Mg–8.0Al–xYb–0.5Zn (wt%, x = 0, 1, 2) cast alloys were investigated. With increasing Yb content, a significant grain refinement was observed, accompanied by the continuous refinement and fragmentation of the initial β-Mg₁₇Al₁₂ phase network. Concurrently, the Al₃Yb phase formed and coarsened. Calculations including formation enthalpy and lattice misfit, confirm that the Al₃Yb phase, which nucleates prior to the α-Mg and β-Mg₁₇Al₁₂ phases and exhibits a low lattice misfit with their low-index planes, serves as an effective heterogeneous nucleation site, significantly contributing to the observed microstructural refinement. Furthermore, Yb addition fundamentally suppresses constitutional supercooling by consuming Al atoms, which possess a high growth restriction factor, for the formation of Al–Yb phases. Subsequent tensile testing reveals that Yb solute promotes the generation of extension twins and the accumulation of dislocations during deformation, leading to a marked enhancement in the work-hardening capacity of the Yb-containing alloys. Benefiting from the refined microstructure and enhanced work hardening, the Mg–8.0Al–1.0Yb–0.5Zn alloy exhibits a favorable balance between mechanical strength and ductility, achieving an ultimate tensile strength of ~ 249.8 MPa and an elongation of ~ 11.70%, respectively.

Previous studies on SnTe have indicated that its low ZT value is associated with a high carrier concentration of up to 10²⁰–10²¹ cm⁻³ and an excessively high lattice thermal conductivity. However, the high carrier concentration and lattice thermal conductivity observed in SnTe are not solely attributable to the presence of numerous intrinsic tin vacancies and a simple crystal structure. Additionally, the oxides formed through the oxidation of Sn and SnTe exert a partial influence on these properties. In this study, by pretreating the raw Sn material and isolating it from oxygen during preparation, we achieve a significant improvement in the thermoelectric performance of binary SnTe at high temperatures, with a peak ZT of approximately 0.83 at 800 K. This approach effectively reduces the content of SnO₂ in the matrix, enhancing the electrical and thermal transport properties of the samples. Specifically, the high-thermal conductivity of SnO₂ facilitates the formation of channels at grain boundaries that are more conducive to heat transfer, while its poor electrical conductivity and Seebeck coefficient diminish the intrinsic electrical transport behavior of SnTe. The removal of SnO₂ reflects the true thermoelectric performance of SnTe, making the samples prepared by this method stand out compared to other reported binary SnTe materials.

Medium-manganese steel exhibits excellent strength and toughness, which are essential features in wear resistance applications. This study examines the impact of annealing temperature on impact abrasive wear. The results have indicated that samples annealed at different temperatures display plowing and fatigue wear effects. In the initial wear stage, the high-temperature annealed steel outperforms samples annealed at a lower temperature in terms of anti-plowing wear performance. This phenomenon is mainly due to the lower initial hardness of the samples subjected to low-temperature annealing. However, with prolonged wear time, the low-temperature annealed samples exhibit improved plowing wear performance, which is ascribed to a refinement of the lamellar microstructure and an increased residual austenite (RA), which enhances the work hardening effect, improving the hardness of the worn surface. The low-temperature annealed samples consistently delivered superior fatigue wear performance when compared with samples annealed at the higher temperature. The latter effect may be attributed to two factors. Firstly, the finer lamellar microstructure in the low-temperature annealed samples, coupled with greater RA, results in transformation-induced plasticity or twin-induced plasticity effect that hinders crack formation and propagation. Secondly, the low-temperature annealed samples form nanoscale equiaxed grains near the worn surface during the wear process. These grains can withstand crack driving forces in fine-grained regions, suppressing the formation and propagation of cracks.

Surface nanocrystallization is a practical approach to enhance surface wear resistance, whereas the specific mechanism of how surface nanocrystallization affects the wear resistance of NbMoTaW refractory high-entropy alloys (RHEAs) remains unclear. Herein, we performed molecular dynamics simulations to explore the wear behaviors of nanograined NbMoTaW RHEA during surface scratching. The wear resistance of nanograined models was significantly enhanced compared to the single-crystalline counterpart. As the grain size increases, the dominant plastic deformation mechanism switches from grain boundary deformation to dislocation movement. Notably, the model with a grain size of 20 nm exhibits the highest dislocation density, local stress, and degree of work hardening. At elevated temperatures, the dynamic recrystallization becomes a crucial plastic deformation mechanism and hinders the formation of dislocations, resulting in a decrease in dislocation density and consequently a decline in the wear resistance of NbMoTaW RHEAs. The current study provides insight into the mechanism underlying the enhanced wear resistance of NbMoTaW RHEAs.