Acta Metallurgica Sinica-English Letters最新文献

The restoration mechanism of twin-induced plasticity (TWIP) steel during friction stir welding (FSW) changed with the degree of the deformation, and the microstructure evolution and dynamic recrystallization are complex and unclear. In this paper, the electron backscattered diffraction and transmission electron microscopy techniques were used to evaluate the dynamic grain structure of FSW joint of TWIP steel. The results showed that the dynamic recrystallization mechanisms in TWIP steel during FSW contained discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). The recrystallization mechanism transitioned from DDRX at the initial deformation stage to DDRX and CDRX at the middle deformation stage, eventually becoming primarily CDRX at the end deformation stage. Numerous annealing twin boundaries (ATBs) were formed within the joint, and the straight ATBs primarily resulted from grain growth accidents, while cluster-shaped ATBs were formed through re-excitations and decomposition of specific grain boundaries.

This study investigated the effect of pressure, pre-charge time, punch velocity and oxygen content on the mechanical properties of X42 pipeline steel in gaseous hydrogen environment by using small punch test. When exposed to nitrogen, the fracture mode of X42 pipeline steel undergoes ductile fracture, but in the presence of hydrogen, it shifts to brittle fracture. Moreover, an increase in hydrogen pressure or a decrease in punch velocity is found to enhance the hydrogen embrittlement susceptibility of X42 pipeline steel, as evidenced by the decrease of maximal load, displacement at failure onset and small punch energy. But the effect of pre-charge time on the hydrogen embrittlement susceptibility of X42 pipeline steel is not very obvious. Meanwhile, the presence of oxygen has been found to effectively inhibit hydrogen embrittlement. As the oxygen content in hydrogen increases, the hydrogen embrittlement susceptibility of X42 pipeline steel decreases.

Magnesium alloys have large reserves and good strength, attracting a lot of attention. Herein, the thermodynamic, elastic constants, and electronic properties of the Mg-Y-Zn ternary compounds were calculated; among them, MgYZn₂ belongs to the cubic structure, MgYZn, Mg₃Y₂Zn₄, and Mg₁₄YZn-1 belong to the hexagonal structure, Mg₆YZn-1, Mg₆YZn-2, MgY₂Zn, and Mg₁₄YZn-2 possess the orthorhombic structure, and Mg₃Y₂Zn₃ is trigonal structure. The calculated cohesive energies of the results show that all compounds are thermodynamically stable. Moreover, the MgYZn₂ compound exhibits the highest modulus of 76.84 MPa, and the Mg₃Y₂Zn₃ has the biggest hardness of 6.6 GPa. In addition, the Mg₆YZn-2 has the strongest elastic anisotropic with A^U of 6.14 and A_G of 0.38, respectively. According to the population analysis, the Mg-Y covalent bond is due to the biggest bond population. The shortest weighted average bond length indicates that MgYZn₂ has better elastic properties. Furthermore, the calculated limiting thermal conductivity results show that Mg₁₄YZn-2 has better thermal conductivity with maximum values of 0.94 W·m⁻¹·K⁻¹ and 0.74 W·m⁻¹·K⁻¹ for Clarke’s and Cahill’s models.

This study used an anodic etching (AE) method to construct a hierarchical rough surface on the surface of the Cu-bearing antibacterial titanium alloy, Ti–xCu (x = 3, 5, 7 wt%), a three-dimensional structure with nested micro-/submicro-pores and internal cavities, which is conducive to the adhesion and growth of bone cells. After AE treatment, with increase of the Cu content in the alloy, the surface of Ti–Cu alloy became sharper, with more fine micropores and internal cavities, thus increasing the surface area. The results indicated that the AE/Ti–Cu alloy exhibited good antibacterial properties and had the effect of inhibiting bacterial biofilm formation. AE treatment could increase the Cu ions release of Ti–Cu alloy in saline, and the higher the Cu content in the alloy, the more Cu ions release, resulting in stronger antibacterial performance of the alloy. AE/Ti–Cu alloy showed excellent biocompatibility, similar to the pure Ti. Therefore, anodic etching is a safe and effective surface treatment method for Ti–Cu alloy, with good clinical application prospects.

In this work, Mg(0001)/AlB₂(0001) interfaces with various terminations and stacking orders were constructed, and the atomic and electronic structures and adhesion work (W_ad) of the interface were investigated using the first-principles calculations. Notably, during the geometry optimization process, the B-mid-top (B-MT) Mg(0001)/AlB₂(0001) interface exhibits the most significant interface changes and manifests the least stability. Horizontal movement of Mg atoms in the first layer of the Mg surface slab, along the normal direction, results in a structure akin to the structurally optimized hexagonal close-packed (HCP) interface. The B-HCP interface demonstrates the highest stability, the largest ideal W_ad, and the smallest interface distance. The interface enhances the binding strength of the Mg-side sub-interface, but diminishes the binding strength of the AlB₂-side sub-interface. Furthermore, Mg atoms can form metallic/covalent mixed bonds with Al atoms on the Al-terminal AlB₂ surface and form ionic bonds with B atoms on the B-terminal AlB₂ surface. Mg(0001)/AlB₂(0001) interface has good bonding properties. This research provides strong theoretical support for an in-depth understanding of Mg/AlB₂ interface characteristics.

The effects of Ta on the tensile behavior and deformation mechanisms of a Ni-based single crystal superalloy were investigated in this study from room temperature to elevated temperature. The findings demonstrated that the higher content of Ta could improve the tensile properties of the alloy at different temperatures. Due to the different deformation mechanisms at various temperatures, the influence of Ta on tensile deformation varied. At room temperature, the higher content of Ta enhanced the solid solution strengthening, which would enhance the tensile strength of 6.5Ta alloy. After standard heat treatment of 6.5Ta alloy, precipitation of the secondary γʹ phase would hinder the movement of dislocations. When the temperature was elevated to 760 °C, the higher content of Ta not only promoted the interaction of stacking faults to form Lomer–Cottrell (L-C) locks that impeded dislocation motion, but also reduced the occurrence of dislocation pile-up groups, thus enhancing the yield strength. At 1120 °C, due to the narrower γ channels and higher APB energy in γʹ phase of the alloy with higher Ta addition, the processes of bypassing and shearing of dislocations were hindered, respectively. Meanwhile, the denser and more regular dislocation networks were formed in 6.5Ta alloy; and thus, the tensile strength of 6.5Ta alloy was enhanced. This study systematically investigated the effect of Ta on the tensile behavior at three different temperatures, which provided an important theoretical basis for the design of nickel-based single crystal superalloys in the future.

Understanding the effects of various elements on solidification behavior is crucial for designing the composition of γ’-strengthened Co-based superalloys and is fundamental for controlling the as-cast structure and formulating subsequent heat treatment processes. This research investigated the effects of replacing 1 at.% W with 1 at.% Nb or Hf elements on the solidification behavior of Co–Ni–Al–W-based superalloys. The findings revealed that substituting W with Nb and Hf resulted in a notable decrease in both the solidus temperature (T_S) and liquidus temperature (T_L). Specifically, the substitution of W with Nb lowered T_S from 1353 °C to 1332 °C and T_L from 1383 °C to 1368 °C, while replacing W with Hf decreased T_S from 1353 °C to 1330 °C and T_L from 1383 °C to 1366 °C. Moreover, both Nb and Hf element are positive segregation element, while Nb decreases and Hf increases W segregation, respectively. During the final solidification stage, the substitution of W with Nb resulted in the formation of eutectic (γ + γ’), Co₃Ta, and a small amount of μ-Co₇Nb₆ phase, while replacing W with Hf resulted in the formation of the Laves phase and β-CoAl phase. The solidification paths of the three alloys were confirmed based on the result of differential scanning calorimetry, isothermal solidification experiment and Thermo-calc simulation. These results offer a theoretical basis for the composition design and optimization of heat treatment processes for Co–Ni–Al–W-based superalloys.

Conventional high-strength Mg-RE-based wrought alloys usually contain a high amount of RE solutes, which largely increases the alloy cost and thus restricts their adoptions. In this work, we developed a low-RE-containing Mg-3Sm-1Nd-0.6Zn-0.4Zr alloy by hot extrusion with low extrusion ratio, which shows a high tensile yield strength (TYS) of 435 MPa and a satisfactory elongation of 5.6% at room temperature, outperforming most Mg-Gd-Y-based extrusion alloys with RE contents of 12 wt% at least. Outstanding high-temperature strength, such as the TYS of 280 MPa at 200 °C and 251 MPa at 250 °C, is also obtained in this alloy. The alloy presented a typical bimodal grain structure including coarse hot-worked grains with a strong texture and fine recrystallized grains with random orientations. Also, abundant Mg₃RE particles were mostly introduced in hot-worked grains and at recrystallized grain boundaries by dynamic precipitation during extrusion. Consequently, the high strength of this alloy is principally attributed to the combined hardening effect of numerous Mg₃RE particles, fine recrystallized grains, and strongly textural hot-worked grains, rather than the ultra-strong age-hardening effect in traditional high RE-alloyed Mg alloys.

The strength and ductility cannot achieve a good tradeoff for some superalloy (e.g. GH3536) prepared by selective laser melting (SLM), which seriously restricts their industrial applications. This work examined the effect of post-heat treatment (HT) on the microstructure and mechanical properties of GH3536 produced by SLM. In particular, the influence of carbide precipitate morphology and distribution on strength and ductility of the alloy after heat treatment was discussed. After aging at 650 °C (denoted as HT1), the Cr₂₃C₆ carbides were distributed in chains. The ductility increased by approximately 31%, while the strength slightly decreased. After aging at 745 °C (denoted as HT2), the Cr₂₃C₆ carbides were distributed in chains. However, the HT2 samples showed an increase in ductility of ~ 58% and no reduction in strength. As the dislocation density of HT2 sample was higher than that of the HT1 sample, the chain carbides could be pinned to the grain boundaries, consequently improving the ductility but no loss in strength as compared with the as-deposited samples. When the aging temperature was increased to 900 °C (denoted as HT3), the carbides were distributed in a discontinuous granular form. As a result, the HT3 samples presented the lowest dislocation density which reduced the strength.

Magnesium alloys have a significant advantage, lower density over the other structure materials; hence, they have been widely used in various fields such as transportation and aerospace. With the development of research and the enlargement of the research scope, more advantages have been revealed: excellent shielding efficiency, extraordinarily high damping capacity, as well as impressive thermal conductivity. Therefore, Mg alloys have the potential to be various functional materials, such as electromagnetic shielding material, damping material, and thermal conductive material. This review comprehensively summarizes the research progress and the up-to-date summary of Mg alloys as structure–function integrated materials in recent years. Solute atoms, heat treatment, deformation, secondary phase, and temperature, which have a significant influence on the properties of magnesium alloys, are highlighted. We expect this review to be helpful for those who are working on developing structure–function integrated materials with superior comprehensive performance.