Acta Metallurgica Sinica-English Letters最新文献

Metallic magnesium and its alloys, as new types of metallic structural materials, show great application potential in fields such as aerospace, electronics, and biomedicine. However, magnesium is chemically active and highly susceptible to oxidation and corrosion in various environmental conditions, which can compromise its structural integrity and significantly reduce its service life. Therefore, it is of great significance to strengthen the development and application of corrosion protection technology for magnesium materials. At present, the nitridation of magnesium and its alloys is regarded as an effective surface treatment method to enhance corrosion resistance. To create durable nitrided layers on magnesium substrates with long-term stability, it is essential to thoroughly comprehend the influence of various techniques and processing conditions, as well as the resulting layer composition and microstructure. Additionally, a detailed understanding of how these fabricated layers behave in corrosive environments is crucial for optimizing their performance. This paper systematically reviews the research achievements and latest progress in the surface nitridation on magnesium alloys. The principles, advantages, drawbacks of different nitridation process, as well as their applications in enhancing the corrosion resistance of magnesium alloys are discussed. Furthermore, the paper summarizes the main technologies in the fabrication of magnesium nitride films, such as pulsed laser deposition, low-pressure chemical vapor deposition, reactive magnetron sputtering, thermal plasma synthesis, and molecular beam epitaxy, which offers a valuable reference for experimental research on magnesium nitride film. Finally, it also discusses the challenges and prospects of the research on the surface nitriding of magnesium and its alloys.

Graphene is considered promising reinforcement for improving the mechanical properties of the titanium alloys. However, overcoming the strength–ductility trade-off in graphene-reinforced titanium composites remains a challenge. In this study, the high-performance graphene nanoplatelets (GNPs) reinforced Ti–6Al–4V (TC4) matrix composites were successfully synthesized by combining the hot-pressing sintering and hot-rolling methods. Studies on the effect of GNPs on microstructures and properties of the as-sintered and as-rolled TC4 composites were systematically conducted. It indicates that the strength of the composites can be substantially enhanced by the addition of GNPs, primarily attributable to grain refinement and the pinning effect induced by in situ formed TiC particles. Moreover, the increase in the GNPs content results in a decrease in the plasticity of the as-sintered composites due to the aggregation of TiC. Additionally, hot rolling synchronously enhances the strength and plasticity of the composites by facilitating the homogeneous dispersion of TiC within the TC4 matrix. This work provided a potential strategy in designing the graphene-reinforced TC4 matrix composites with superior strength–ductility synergy.

Ni-based superalloys play a critical role in the aerospace industry due to their exceptional mechanical properties and oxidation resistance. However, the conventional development of new superalloys is often constrained by lengthy experimental cycles and high costs. To address these challenges, machine learning has emerged as an effective strategy for accelerating alloy design by efficiently exploring composition–property relationship, optimizing processing parameters, and enhancing predictive accuracy. This review summarizes recent progress in applying machine learning to composition optimization and mechanical property prediction of Ni-based superalloys, emphasizing the integration of theoretical modeling and experimental validation. The importance of feature engineering, including data collection, preprocessing, feature construction, and dimensionality reduction, was first highlighted. Subsequently, the machine learning approaches for novel alloy design and prediction of key properties including fatigue resistance, creep resistance, and oxidation resistance were discussed. Through data-driven approaches, machine learning not only enhances predictive capabilities but also uncovers complex composition–property relationship, which accelerates the development of next-generation Ni-based superalloys. We anticipate that the continued advancements in this field will drive more efficient and cost-effective alloy design, ultimately accelerating the transition from computational predictions to experimental realizations.

The nano-scale L1₂-Ni₃Al precipitates significantly contribute to thermal stability of alumina-forming austenitic (AFA) steels. The coarsening behavior of L1₂-Ni₃Al precipitates in AFA steels during isothermal aging with considering the influence of alloying elements was investigated. The results show that the coarsening rate of L1₂-Ni₃Al precipitates increases with co-additions of Ni and Cu, and especially, the increase of Cu content promotes the nucleation of L1₂-Ni₃Al precipitates. A dynamic competition exists between Lifshitz–Slyozov–Wagner theory and transient interface diffusion-controlled theory for coarsening behavior of L1₂-Ni₃Al precipitates with duration of isothermal aging. Additionally, the transition from L1₂-Ni₃Al precipitates to B2-NiAl precipitates during isothermal aging results in the formation of a depleted zone of L1₂-Ni₃Al precipitates around B2-NiAl precipitates, which inhibits the growth of L1₂-Ni₃Al precipitates. The coarsening of L1₂-Ni₃Al precipitates significantly contributes to the yield strength of AFA steels.

Hydrogen embrittlement (HE) remains a critical challenge for high-strength steels. This study comparatively investigates the HE behavior and hydrogen diffusion characteristics of a vanadium-micro-alloyed 42CrNiMoV steel against conventional 40CrNiMo steel through slow strain rate testing (SSRT), hydrogen thermal desorption, and hydrogen permeation measurements. The 42CrNiMoV steel demonstrated better mechanical properties and improved HE resistance under SSRT with both hydrogen pre-charged and in situ charging conditions. Microstructural analysis revealed that vanadium micro-alloying leads to grain refinement and reduces hydrogen diffusivity through vanadium carbides. Fractographic investigations revealed the environment-dependent fracture mechanisms, transitioning from ductile- to brittle-dominated failure modes under different hydrogen-charging conditions. These findings validate that vanadium micro-alloying represents a promising, cost-effective strategy for developing hydrogen-resistant high-strength steels, while emphasizing the crucial need for rigorous hydrogen ingress control in practical applications.

Pure titanium fabricated by powder metallurgy generally encounters problems including low relative density and low strength, which limits its application performance. This work proposed a multi-step pressing (MSP) technique for developing high-strength pure titanium. The MSP processes of spherical Ti powders of 15–53 μm, 53–105 μm, and 75–180 μm were systematically investigated through multi-particle finite element method (MPFEM) compared with conventional one-step pressing (OSP) technique. The relative density, phase constitution, microstructure, and compressive mechanical properties of the sintered bulk pure titanium were characterized. Simulation results demonstrate that the MSP technique significantly increases the relative density of green compacts by 3.2%, 3.3%, and 5.2%, respectively, compared with OSP technique. Experimental results indicate the relative density of the sintered specimens prepared by MSP spherical powders increases by 5.4%, 4.5%, and 4.5%, respectively, compared to OSP, and the yield strength improves by 16%, 13%, and 18%. For the sintered specimens prepared by MSP irregular powder of 15–53 μm, the relative density increases by 6.0% and the yield strength increases by 15%. The enhancement of relative density and yield strength is mainly because the MSP technique mitigates stress concentration between powder particles. Compared to spherical powder, irregular powder exhibits stronger mechanical interlocking owing to the greater propensity for displacement and deformation, which facilitates mutual wedging and interlocking, resulting in superior strength performance.

The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming. This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongation exceeding 230% in a coarse-grained Ni-Co-based superalloy. The deformed microstructure and fractographic characteristics of the alloy were examined utilizing optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The results of the analysis revealed that below 1100 °C, the process of dynamic recrystallization (DRX) occurred at a sluggish rate, resulting in low plasticity and the initiation of severe cracks. Complete DRX occurred when the deformation temperature exceeded 1100 °C, leading to a more uniformly deformed microstructure, reduced crack initiation, and enhanced ductility demonstrated by elongation to failure surpassing 230%. The augmented occurrence of the DRX facilitated prolonged plastic-forming periods, which delayed fracture propagation and promoted the deformation flow within the alloy, thereby transitioning the fracture behavior from intergranular-brittle at 1050 °C to ductile intergranular at 1140 °C. At this temperature, the deformation was predominantly governed by the discontinuous-DRX (DDRX) mechanism and grain growth, facilitated by the formation of twin boundaries.

The widespread application of magnesium (Mg) and Mg alloys is limited by their poor corrosion resistance. Micro-arc oxidation (MAO) is a common surface treatment, but the inherent defects of the MAO coating require post-treatment to ensure good corrosion protection. Therefore, various zeolitic imidazolate framework ZIF-67@Co-M (M = Fe, Al, Ni) layered double hydroxides (LDHs) composite coatings were fabricated on MAO-treated AZ31 Mg alloy to enhance its corrosion resistance. The surface characteristics, coating thickness, corrosion resistance and protection mechanisms of the ZCM (ZIF-67@Co-M LDHs) composite coatings were examined. The findings indicate that the ZCF (ZIF-67@Co-Fe LDHs) composite coating exhibits the lowest corrosion current density (i_corr = 7.76 × 10^–8 A/cm²), superior corrosion resistance, the lowest corrosion rate (HEV = 2.46 mL·cm^–2) and the fastest response speed to corrosion. The synergistic integration of ZIF-67 and LDHs effectively prevents the invasion of corrosive media, enhancing both short-term and long-term corrosion resistance of AZ31 alloys. These composite coatings surpass the limitations of individual materials, providing a promising strategy for durable corrosion protection.

Zinc (Zn) and its alloys are considered promising biodegradable metallic materials for biomedical implants. However, the correlation between the dynamic degradation evolution of Zn and its biocompatibility remains unclear. This study evaluates the long-term degradation/corrosion behavior of pure Zn under dynamic immersion in Hank’s solution containing bovine serum albumin (BSA), and investigates the impact of its dynamic degradation evolution on cytocompatibilities of the representative human umbilical vein endothelial cells (HUVECs) and bone marrow mesenchymal stem cells (BMSCs). Degradation behavior results demonstrate that the dynamic fluidic medium led to speeding-up of the corrosion rate of Zn and exacerbation of the localized corrosion, with this phenomenon being more pronounced under influence of BSA. Correspondingly, the cells’ viability increased with prolonged immersion time under both static and dynamic conditions, alleviating a certain level of cytotoxicity initiated at an earlier stage. Nonetheless, as compared to the static cases the dynamic fluidic environments induced a poorer cell viability, although the BSA helped to offset this impact. Our findings provide not only new insights into better-understanding Zn-based biodegradable metals but also clarify the critical concern in their clinical translations, offering therefore important guidance for development of new biodegradable metallic medical implants.

In this work, the effect of Pseudomonas aeruginosa (P. aeruginosa) on the corrosion behavior of 2219 aluminum alloy manufactured through additive friction stir deposition (AFSD) was investigated. Under sterile conditions, a large number of corrosion products appeared on the sample surface, and the maximum corrosion pit depth reached 5.98 μm after 7 days of immersion. In the presence of P. aeruginosa, the sample surface was extensively colonized by a substantial biofilm, and the maximum pit depth was only 2.88 μm after 7 days of immersion. In addition, electrochemical tests demonstrated a two orders of magnitude reduction in corrosion current density compared to the sterile conditions. The scanning electrochemical microscopy (SECM) results also showed a weakening in the cathodic oxygen reduction process on the sample surface under inoculation conditions. The corrosion resistance of 2219 aluminum alloy manufactured through AFSD was enhanced by the colonization of P. aeruginosa biofilm, primarily attributed to the protective effect exerted by extracellular polymeric substances (EPS) within the P. aeruginosa biofilm.