Acta Metallurgica Sinica-English Letters最新文献

Additive manufacturing (AM) technologies, with their high degree of flexibility, enhance material utilization in the fabrication of large magnesium alloy parts, effectively meeting the demands of complex geometries. However, research on the corrosion resistance of magnesium alloy components produced via AM is currently limited. This study investigates the microstructural and corrosion characteristics of AZ91D magnesium alloy fabricated by wire arc additive manufacturing (WAAM) compared to its cast counterpart. A large-sized AZ91D bulk part was deposited on an AZ31 base plate using a layer-by-layer stacking approach. The results showed that the WAAM AZ91D was featured by obviously refined grains from 228.92 μm of the cast one to 52.92 μm on the travel direction-through thickness (TD-TT) and 50.07 μm on the normal direction-through thickness (ND-TT). The rapid solidification process of WAAM inhibited the formation of β-Mg₁₇Al₁₂ phase while promoting the formation of uniformly distributed network of dislocations, the dispersive precipitation of nano Al₈Mn₅ phase, as well as Zn segregation. WAAM AZ91D demonstrated the occurrence of pitting corrosion and inferior corrosion resistance compared to cast AZ91D, attributed to the micro-galvanic corrosion between the α-Mg matrix and Al₈Mn₅ particles and the increased number of grain boundaries.

This study investigated the effects of ultrasonic shot peening (USSP) treatment at various durations on the corrosion resistance and antibacterial properties of 304 Cu-bearing stainless steel (304-Cu SS). The results showed that USSP treatment refined the surface microstructure, enhancing hardness, wear resistance, and dislocation density. With longer treatment time, grain size decreased, and martensitic phase formation was promoted, improving mechanical properties. However, extended USSP treatment induced internal stresses, negatively affecting corrosion resistance. Cu addition to 304 stainless steel resulted in large Cu-rich phases, leading to uneven elemental distribution and reduced corrosion resistance. USSP effectively fragmented these phases, promoting a uniform distribution and enhancing the formation of a dense passive film, with the 304-Cu-5 min coupon showing the best corrosion performance. Cu also significantly improved antibacterial properties, demonstrating strong activity against Eescherichia coli and Staphylococcus aureus after 72 h. Overall, USSP treatment optimized both corrosion resistance and antibacterial performance, with the 5 min treatment providing the best balance.

Ti750s titanium alloy, a novel high-temperature titanium alloy designed for short-term service at elevated temperatures (700–750 °C), has previously lacked comprehensive understanding of its hot processing behavior. In this study, the high-temperature deformation behavior and microstructural evolution of the Ti750s alloy were systematically investigated through thermal simulation compression tests conducted at temperatures ranging from 900 to 1070 °C and strain rates between 0.1 and 10 s⁻¹. A hot processing map was constructed using the dynamic material model to optimize the hot processing parameters. The results indicated that the optimal processing window was between 1040 and 1070 °C with a strain rate of 0.1 s⁻¹. Processing within the instability region resulted in localized plastic deformation, manifesting as pronounced shear bands and a highly heterogeneous strain distribution; this region should be avoided during hot deformation. Within the α + β phase safety zone characterized by low power dissipation rates between 0.32 and 0.4, the primary deformation mechanism in this region was dynamic recovery (DRV), where the lamellar α grains underwent deformation and rotation. Conversely, in the α + β phase safety zone with high-power dissipation rates between 0.45 and 0.52, dynamic spheroidization of the α phase and dynamic recrystallization (DRX) of the β phase occurred concurrently. In the β phase safety zone with low power dissipation rates between 0.32 and 0.51, the primary deformation mechanism consisted of DRV of β grains, accompanied by limited DRX. However, in the β phase safety zone with high-power dissipation rates exceeding 0.56, both DRV and DRX of β grains took place, resulted in a significant increase in the size and number of recrystallized grains compared to those observed under low power dissipation conditions.

Additive manufacturing (AM), as an advanced manufacturing technology, enables the production of personalized orthopedic implant devices with complex geometries that closely resemble bone structures. Titanium and its alloys are extensively employed in biomedical fields like orthopedics and dentistry, thanks to the excellent compatibility with the human body and high corrosion resistance due to the existence of a thin protective oxide layer known as TiO₂ upon exposure to oxygen on the surface. However, in joint inflammation, reactive oxygen species like hydrogen peroxide and radicals can damage the passive film on Ti implants, leading to their deterioration. Although AM technology for metallic implants is still developing, advancements in printing and new alloys are crucial for widespread use. This work aims to investigate the corrosion resistance of in-situ alloyed Ti536 (Ti5Al3V6Cu) alloy produced through electron beam powder bed fusion (EB-PBF) under simulated peri-implant inflammatory conditions. The corrosion resistance was evaluated using electrochemical experiments conducted in the presence of 0.1% H₂O₂ in a physiological saline solution (0.9% NaCl) to replicate the conditions that may occur during post-operative inflammation. The findings demonstrate that the micro-environment surrounding the implant during peri-implant inflammation is highly corrosive and can lead to the degradation of the TiO₂ passive layer. Physiological saline with H₂O₂ significantly increased biomaterial open circuit potential up to 0.36 mV vs. Ag/AgCl compared to physiological saline only. Potentiodynamic polarization (PDP) plots confirm this increase, as well. The PDP and electrochemical impedance spectroscopy (EIS) tests indicated that adding Cu does not impact the corrosion resistance of the Ti536 alloy initially under simulated inflammatory conditions, but prolonged immersion leads to enhanced corrosion resistance for all biomaterials tested, indicating the formation of an oxide layer after the reduction of the solution oxidizing power. These results suggest that modifying custom alloys by adding appropriate elements significantly enhances corrosion resistance, particularly in inflammatory conditions.

As functional materials capable of direct thermoelectric energy conversion, thermoelectric materials hold immense promise for waste heat recovery and sustainable energy utilization. Through development in recent decades, many thermoelectric material systems with excellent performance have been developed. In alignment with the principles of circular economy and sustainable development, the search for new and efficient thermoelectric materials has become one of the most important directions of current research. SnSe has received much attention as an environmentally friendly and cost-effective thermoelectric material system. In particular, polycrystalline SnSe, with the advantages of facile preparation and stable mechanical properties, is suitable for large-scale industrial production. Here, we summarize the common preparation methods of polycrystalline SnSe in the decade of melting, mechanical alloying, and liquid-phase methods, as well as the strategies of property optimization such as microstructure design, grain boundary engineering, and band engineering. Finally, we provide perspectives on future research directions for polycrystalline SnSe to further improve thermoelectric performance and accelerate its practical applications.

The low-density medium-Mn steel is widely studied and applied in the automobile and construction machinery due to the low costs and high strength-ductility. Adding lightweight elements, such as aluminum, is considered an efficient way to reduce the density of the steels. A novel 5Al-5Mn-1.5Si-0.3C (wt%) low-density and high-strength δ-ferrite/martensite (δ-F/M) steel was designed in this study. The study indicated that the designed steel annealed at 1080 °C was characterized by an excellent combination of tensile strength of 1246 MPa and density of 7.24 g/cm³. Microscopic characterization shows that the higher prior-austenite volume fraction (i.e., martensite plus retained austenite) significantly increases the tensile strength, and the strip-like martensite and retained austenite (M&RA) mixture benefits elongation. High martensite fraction owns higher origin geometrically necessary dislocations, contributing to better work-hardening behaviors. Concurrently, the synergistic presence of M&RA mixtures’ volume fraction and morphology enhances their capability to absorb stress and obstruct crack propagation, significantly improving mechanical performance. The extended strength formula, accounting for the contribution of the M&RA mixture, is consistent with the quantitative agreement observed in experimental results. These insights provide a valuable technological reference for the knowledge-based design and prediction of the mechanical properties of low-density and high-strength steel.

Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel, while pulsed current can accelerate atomic diffusion to achieve ultra-fast spheroidization of carbides. However, the understanding of the mechanism by which different pulse current parameters regulate the dissolution behavior of carbides requires a large amount of experimental data to support, which limits the application of pulse current technology in the field of heat treatment. Based on this, quantify the obtained pulse current processing data to create an important dataset that could be applied to machine learning. Through machine learning, the mechanism of mutual influence between carbide regulation and various factors was elucidated, and the optimal spheroidization process parameters were determined. Compared to the 20 h required for traditional heat treatment, the application of pulsed electric current technology achieved ultra-fast spheroidization of GCr15 bearing steel within 90 min.

The effects of drawing strain during intermediate annealing on the microstructure and properties of Cu-20 wt% Fe alloy wires while maintaining constant total deformation were investigated. Intermediate annealing effectively removes work hardening in both the Cu matrix and Fe fibers, restoring their plastic deformation capacity and preserving fiber continuity during subsequent redrawing. The process also refines the Fe phase, leading to a more uniform size distribution and straighter, better-aligned Cu/Fe phase interfaces, thereby enhancing the comprehensive properties of the alloy. The magnitude of drawing strain during intermediate annealing plays a critical role in balancing the mechanical strength and electrical conductivity of redrawn wires. A lower initial drawing strain requires greater redrawing strain, leading to excessive hardening of the Fe fibers, which negatively impacts the electrical conductivity and tensile plasticity. Conversely, a higher initial drawing strain can result in insufficient work hardening during the redrawing deformation process, yielding minimal strength improvements. Among the tested alloys, H/3.5 wires show a slight reduction in strength and hardness compared to W and H/4.5 wires but exhibit a significant increase in tensile elongation and electrical conductivity. The tensile strength was 755 MPa, and the electrical conductivity was 47% international-annealed copper standard (IACS). The optimal performance is attributed to the formation of a high-density, ultrafine Fe fiber structure-aligned parallel to the drawing direction, which is achieved through a suitable combination of the drawing process and intermediate annealing.

To investigate the influence of W and Al on the microstructure and mechanical properties of a high-W superalloy, the Thermo-Calc calculation was utilized to simulate the microstructure with various W and Al contents. The results indicated that the concentration of W and Al exceeded 15.7 wt% and 5.9 wt%, respectively, the abnormal tungsten-rich α-W phase would precipitate. Compared with the results of orthogonal experiment, the precipitation of α-W phase is consistent with thermodynamic calculation results. The presence of Al not only influenced the precipitation of α-W phase but also impacted the eutectic content and the γʹ-size, both of which showed an increase with higher Al concentrations. Excessive W and Al contents promoted the precipitation of α-W phase, escalating the site of crack nucleation, and ultimately decreasing the plasticity. In the process of creep deformation (975 °C / 235 MPa), the rafted γ' phases were more continuous with increasing W contents, which increased the difficulty of dislocation climbing. As Al content increased, the density of interfacial dislocation network increased. The dislocations were entangled with each other, and the hindrance of dislocation movement was enhanced, which improved the stress rupture life. However, the precipitation of the hard and brittle α-W phase was attributed to the excessive W and Al, which increased the tendency of crack formation and significantly diminished the stress rupture life. The alloy exhibited the highest stress rupture life of 110.46 h when the W and Al contents were 15.7 wt% and 5.9 wt%, respectively.

The synergistic cooling of thermoelectromagnetic materials promises a breakthrough in the efficiency of single refrigeration and has attracted extensive research. The study of heterogeneous interface is crucial for achieving the synergistic performance of both materials. In this work, a composite material comprising Bi₂Te₃-based thermoelectric material and MnCoGe-based magnetocaloric material is synthesized, which is a material exhibiting both thermoelectric and magnetocaloric properties. During the plasma-activated sintering process of the composite material, elemental interdiffusion of Mn, Co, Sb, and Te occurs, forming a diffusion layer of MnTe and CoSbTe. Reaction of heterogeneous interface leads to point defects within the material, significantly increasing the carrier concentration. Optimization of the sintering temperature results in a thermoelectric figure of merit (ZT) of 0.69 at 300 K and −ΔS_max of 0.97 J kg⁻¹ K⁻¹ at room temperature under a 5 T magnetic field for the Bi_0.5Sb_1.5Te₃/10 wt% Mn_0.9Cu_0.1CoGe composite sintered at 623 K and under 50 MPa. This study demonstrates that Bi_0.5Sb_1.5Te₃/Mn_0.9Cu_0.1CoGe is a potential candidate for efficient thermoelectromagnetic cooling applications.