Acta Metallurgica Sinica-English Letters最新文献

A dilute Mg–0.7Al–0.3Ca (AX0703, wt%) alloy with high strength is developed via conventional low-temperature extrusion, with tensile yield strength of 376 MPa and elongation of 5.3%. As-extruded AX0703 sample exhibits the bimodal grain structures consisting of dynamically recrystallized (DRXed) ultrafine grains and coarse non-DRXed grains with strong basal texture, which contributes to the strength. The numerous nano-Al₂Ca phases were developed in non-DRXed grains during extrusion, which not only generates the remarkable precipitation hardening effect, but also favors the improved thermal stability by retarding recrystallization process. Also, it is found that co-segregations of Al–Ca solutes at DRXed grain boundaries hinder grain growth during heat treatment at 300 °C, contributing to the thermal stability of as-extruded AX0703 alloy. This work provides valuable insights into the development of high-strength and low-alloyed Mg extrusions with high thermostability.

The dissolution behaviors of corrosion products on 316LN stainless steel (SS) in simulated shutdown acid-reducing water chemistry were investigated. The outer Fe- and Ni-rich corrosion products formed in borated and lithiated high-temperature water at 300 °C dissolved under the simulated shutdown acid-reducing water chemistry. NiFe₂O₄ began to dissolve at the initial stage of boration, but the dissolution of Fe₃O₄ mainly occurred at the low-temperature stage in shutdown acid-reducing phase. Low pH value and low-temperature conditions are conducive to the dissolution of the outer Fe-rich oxides. The potential–pH (E–pH) diagrams and solubility curves of spinel oxides at different temperatures were calculated. The possible dissolution mechanism of corrosion products was discussed.

Solute segregation at grain boundaries (GBs) can significantly influence GB cohesion. In this work, the segregation energies of solutes (Zn, Al, Ag, Ca, and Gd) were first investigated at six symmetrical tilt GBs rotating around [0001] axis of Mg, to uncover the impact of GB characteristics on solute segregation behavior. The results reveal that solute segregation propensity is closely related to the local geometric environment of GB sites, but has little correlation with intrinsic GB properties (such as GB misorientation and GB energy). Furthermore, relationships between GB site characteristics and solute segregation tendencies were established. Ca-like solutes tend to occupy GB sites with larger Voronoi volumes (V), while Zn-like solutes prefer GB sites with smaller V as well as smaller shortest bond lengths (SBL). Based on this finding, we further evaluated the segregation capacities of 26 solutes at their most energetically stable segregation sites and their impact on GB cohesion. A descriptor that can effectively capture the strengthening/embrittling potency of segregated solutes on GBs was proposed by performing the crystal orbital Hamilton population (COHP) analyses. It was found that the discrepancies in bond strength between GBs and free surface dominate the solute-strengthening behavior. Finally, a first-principles “design map” regarding the segregation energies and strengthening energies was provided, which offers a database for designing Mg alloys with high fracture toughness.

In the era of big data, reinforcement learning (RL) has emerged as a powerful data-driven optimization approach in materials science, enabling unprecedented advances in material design and performance improvement. Unlike traditional trial-and-error and physics-based approaches, RL agents autonomously identify optimal strategies across high-dimensional and dynamic design spaces by iterative interactions with complex environments. This capability makes RL especially effective for target optimization and sequential decision-making in challenging materials science problems. In this review, we present a comprehensive overview of fundamental RL algorithms, including Q-learning, deep Q-networks (DQN), actor-critic methods, and deep deterministic policy gradient (DDPG). Then, the core mechanisms, advantages, limitations, and representative applications of RL in materials discovery, property optimization, process control, and manufacturing are discussed systematically. Lastly, key future research directions and opportunities are outlined. The perspectives presented herein aim to foster interdisciplinary collaboration and drive innovation at the frontier of AI‑driven materials science.

Mg-8.5Li-5Zn-1Y (wt%) and Mg-8.5Li-7.5Zn-1.5Y (wt%) alloys were prepared by vacuum melting casting method. The thermal flow behavior of the alloys was systematically investigated by isothermal hot compression tests using the Gleeble-3500 thermal mechanical physical simulation system. The tests were conducted under the conditions of the temperature of 473–593 K and the strain rate of 0.001–1 s⁻¹. A modified parameter polynomial constitutive model and thermal processing diagram for the two alloys were constructed. The variation pattern of the unstable region under different Zn and Y contents was analyzed and the safe processing region was determined. The influence of different areas in processing map on dislocation configuration and deformation mechanism was clarified. The results indicate that the higher contents of Zn and Y reduce the instability zone. Processing in the unstable zone only results in < a > slip, while processing in the safe zone initiates < c + a > slip also. The higher contents of Zn and Y reduce the critical deformation temperature for the initiation of < c + a > slip.

The effects of accumulative hot rolling followed by solution treatment on the microstructural evolution and fracture behavior of 30CrMo/316L multilayered composites have been investigated. A scanning electron microscope equipped with an electron backscatter diffraction probe, a laser confocal microscope, an electron probe microanalysis, and a universal testing machine were employed to characterize the microstructures and mechanical properties. The results indicate that solution treatment transformed the microstructure of the 30CrMo layer from ferrite to martensite, while the 316L layer remained austenitic but transitioned from the rolled to the recrystallized state. Additionally, solution treatment significantly enhanced the mechanical properties of the composite, leading to an increase in yield strength and ultimate tensile strength to 744 and 1106 MPa, respectively—258 and 276 MPa higher than those of the hot-rolled plate. The enhancement in strength is primarily attributed to the formation of high-strength martensite in the 30CrMo layer. During deformation, the composite interface effectively impeded crack propagation and induced step-like deflection. However, the formation of cross-layer grains facilitated crack nucleation at grain boundaries, leading to rapid crack propagation and instantaneous fracture. Therefore, preventing the formation of cross-layer grains during the heat treatment process is crucial, as their presence weakens the interfacial strengthening effect of the composite plate. This study provides valuable insights for the design and development of multi-layered steels.

A tri-modal microstructure consisting of equiaxed α phase, acicular α phase and β transformed matrix was achieved in TA15 titanium alloy processed by hot rolling and short-time annealing in this work. The mechanical properties and strengthening mechanisms of TA15 titanium alloy with a tri-modal microstructure were investigated. During the annealing treatment, the volume fraction of acicular α phase decreased gradually with increasing the annealing temperature. Furthermore, with the increase in annealing time, the volume fraction of α phase increased. When the hot-rolled TA15 titanium alloy was annealed at 750 °C for 30 min, a tri-modal microstructure consisting of equiaxed α phase (9.63%/4.56 μm), acicular α phase (70.21%/0.22 μm), and β transformed matrix (20.16%) was obtained. The yield strength, ultimate tensile strength, and elongation of the alloy after annealing at 750 °C for 30 min were 982.8 MPa, 1096.5 MPa, and 11.72%, respectively. The highest strength–ductility product (12,851 MPa%) was obtained for the alloy annealed at 750 °C for 30 min, which exhibited an extraordinary strength–ductility synchronization.

A dislocation density-based crystal plasticity finite element (CPFE) model is developed to reveal the mechanism of discontinuous dynamic recrystallization (DDRX) of the TC17 dual-phase titanium alloy during hot deformation. The model incorporates the temperature and strain rate dependence of nucleation, growth and evolution during DDRX. The evolution of the dislocation densities in the matrix grains (MGs) and the recrystallized grains (RGs) is considered individually. The mechanical response and underlying microstructural evolution are systematically investigated by comparing the CPFE model predictions with experimental tests. The results indicate that at lower temperatures (700 °C and 800 °C), TC17 titanium alloy exhibits a higher volume fraction of recrystallization and a notable drop in flow stress. As the temperature increases (900 °C and 1000 °C), the volume fraction of recrystallization decreases, resulting in a weakened flow stress softening. The nucleation rate of DDRX increases with decreasing deformation temperature and increasing strain rate, while the size of RGs increases with higher temperature and lower strain rate. DDRX nuclei primarily occur at grain boundaries with high dislocation density. Furthermore, DDRX consumes a large number of dislocations and thus reduces the stress concentration and dislocation density at grain boundaries. This study provides a robust model that enhances the understanding of hot deformation mechanisms and informs the design of high-performance titanium alloys for future applications.

The presence of topologically close-packed (TCP) phases is known to deteriorate the mechanical properties of Ni-based single crystal (SX) superalloy, which not only depletes the strengthening refractory elements from the γ' phase, but also contributes to the material failure due to the weak TCP/matrix interface. This study explores the interface between σ and γ' in a creep-fractured Ni-based single crystal superalloy, with a specific focus on the atomic interfacial structures and Co segregation. The σ phase was observed to be orientated with γ' as both [110]_σ//[110]_γ' and [4({overline{text{1}}})0]_σ//[011]_γ', but always possess a habit plane of (001)_σ//(1({overline{text{1}}})1)_γ'. Furthermore, significant Co segregation occurred between the σ and γ', leading to the reinforced interfacial strength. Theoretical calculation indicates that the enhanced interfacial strength can be attributed to the accumulated charge density across the σ/γ interface with the Co segregation. These findings provide insight into the TCP/matrix interface and the role of interfacial solute segregation, which would benefit the design of Ni-based SX superalloys.