Acta Metallurgica Sinica-English Letters最新文献

This study investigated the microstructure and mechanical properties of AlNbTiVZr series high-entropy alloys (HEAs) through both experimental studies and density functional theory calculations. Significant improvements in the microstructures and mechanical properties were achieved for the AlNbTiVZr series HEAs by meticulously adjusting the alloy composition and employing homogenization heat treatment. Notably, the specimen designated as Al_0.5NbTiVZr_0.5 demonstrated excellent mechanical properties including a compressive yield strength of 1162 MPa and a compressive strength of 1783 MPa. After homogenization heat treatment at 1000 °C for 24 h, the Al_0.5NbTiVZr_0.5 alloy exhibits brittle-to-ductile transition. Further atomic-scale theoretical simulations reveal that the decrease of Al content intrinsically enhances the ductility of the alloys, thereby indicating that the mechanical properties of the AlNbTiVZr series HEAs were significantly influenced by the chemical composition. Additionally, specific atomic pair formations were observed to adversely affect the microstructure of the AlNbTiVZr series HEAs, particularly in terms of ductility. These findings provide valuable insights for the design and optimization of light weight HEAs, emphasizing the synergistic adjustment of alloy composition and heat treatment processes to achieve a balance between the strength and ductility.

We have investigated the displacement cascade irradiation resistance behavior of a cobalt-free high entropy alloy FeMnNiCr using molecular dynamics simulations. The results show that defects in FeMnNiCr form in small clusters, and their migration is significantly inhibited, leading to a higher defect recombination rate and a lower number of residual defects compared to Ni. Additionally, FeMnNiCr exhibits a longer thermal peak life and lower thermal conductivity compared to Ni, providing a longer time for defect migration and combining. The migration of defect clusters in FeMnNiCr displays three-dimensional properties, attributed to its high chemical disorder. After prolonged irradiation, defects in FeMnNiCr stabilize as small clusters, whereas point defects in Ni tend to form large defect clusters and evolve into dislocations. Considering the feature of absence of the element cobalt, our results imply that FeMnNiCr has great potential in application in nuclear energies.

In this work, the novel Ni-based superalloy GH4065A inertia friction welding (IFW) joints were subjected to the post-welding heat treatments (PWHT) at 730 ℃ for 5 h or 760 ℃ for 5 h, and the differences in microstructure characteristics, local mechanical properties, and fatigue failure life were focused. Furthermore, based on the high-temperature low-cycle fatigue testing and characterization results, the correlation between the microstructure characteristics and low-cycle fatigue damage behavior was systematically analyzed. It was found that there were smaller grains in the thermo-mechanically affected zone (TMAZ) than in the weld zone and heat-affected zone (HAZ), and the boundary region between TMAZ and HAZ was the fatigue failure position of IFW joints under the high-temperature low-cycle fatigue loading. The fatigue testing results showed that the high-temperature fatigue performance for GH4065A IFW joints degenerated with the increase in PWHT temperature. There existed cyclic softening and inhomogeneous fatigue damage in an IFW joint, which was more significant under the 760 ℃ 5 h PWHT condition. Microstructurally, dislocation tangles and cells formed in the boundary region between TMAZ and HAZ under the fatigue loading. The difference in grain size after the IFW process and the inhomogeneous γ′ phrase re-precipitation after the PWHT in the boundary region between TMAZ and HAZ resulted in the local inhomogeneous strengthening, corresponding to uneven plastic deformation and fatigue failure behavior under the fatigue loadings.

Increasing the print quality is the critical requirement for the additive manufactured complex part of aero-engines of nickel-based superalloys. A study of the effects of Co and Nb on the crack is performed focusing on the selective laser melting (SLM) nickel-based superalloy. In this paper, the solvus temperature of γ', crack characteristics, microstructure, thermal expansion, and mechanical properties of SLM nickel-based superalloy are investigated by varying the content of Co and Nb. The alloy with 15Co/0Nb shows the highest comprehensive quality. Nb increases the crack risk and thermal deformation, and then Co accelerates the stress release. Therefore, Co is an extremely important alloying element for improving the quality of SLM nickel-based superalloy. Finally, the crack growth kinetics and the strain difference are discussed to reveal the SLM crack regular that is affected by time or temperature. The analysis work on the effect of alloying elements can obtain an effective foundational theory to guide the composition optimization of SLM nickel-based superalloys.

The coarsening behavior and strengthening effect of L1₂-Ni₃(Ti,Al) precipitates in a face-centered-cubic (FCC) (FeCoNi)₉₂Al_2.5Ti_5.5 high entropy alloy have been systematically investigated. The coherent L1₂ precipitates, uniformly distributed throughout the FCC matrix, consistently retain a spherical shape. The coarsening rate coefficient of precipitate is determined by employing the Philippe-Voorhees (PV) model, suggesting excellent thermal stability. Furthermore, the elemental partitioning and compositional evolution of the L1₂ precipitates is analyzed by atom probe tomography, which identify aluminum (Al) as the slowest diffusion species during the coarsening process. In addition, the precipitation strengthening effect is quantified to ascertain the optimal size of the precipitates. Our study enhances the understanding of precipitate coarsening in high entropy alloys, presenting valuable insights into their thermal stability and mechanical properties.

Medical bone implant magnesium (Mg) alloys are subjected to both corrosive environments and complex loads in the human body. The increasing number of hyperglycemic and diabetic patients in recent years has brought new challenges to the fatigue performance of Mg alloys. Therefore, it is significant to study the corrosion fatigue (CF) behavior of medical Mg alloys in glucose-containing simulated body fluids for their clinical applications. Herein, the corrosion and fatigue properties of extruded Mg-Zn-Zr-Nd alloy in Hank’s balanced salt solution (HBSS) containing different concentrations (1 g/L and 3 g/L) of glucose were investigated. The average grain size of the alloy is about 5 μm, which provides excellent overall mechanical properties. The conditional fatigue strength of the alloy was 127 MPa in air and 88 MPa and 70 MPa in HBSS containing 1 g/L glucose and 3 g/L glucose, respectively. Fatigue crack initiation points for alloys in air are oxide inclusions and in solution are corrosion pits. The corrosion rate of the alloy is high at the beginning, and decreases as the surface corrosion product layer thickens with the increase of immersion time. The corrosion products of the alloy are mainly Mg(OH)₂, MgO and a small amount of Ca-P compounds. The electrochemical results indicated that the corrosion rate of the alloys gradually decreased with increasing immersion time, but the corrosion tendency of the alloy was greater in HBSS containing 3 g/L glucose. On the one hand, glucose accelerates the corrosion process by adsorbing large amounts of aggressive Cl⁻ ions. On the other hand, glucose will be oxidized to form gluconic acid, and then reacts with Mg(OH)₂ and MgO to form Mg gluconate, which destroys the corrosion product film and leads to the aggravation of corrosion and the accumulation of fatigue damage.

Obtaining an appropriate grain size is crucial for Al alloys or Al matrix composites prior to processing, as it significantly influences the mechanical properties of components and workability during the manufacturing process. TiB₂ particles are exceptional grain refiners in Al and serve as excellent reinforcement particles for particulate-reinforced aluminum matrix composites. However, the optimal particle content for achieving excellent refinement and strengthening effects depends on the matrix composition and requires further investigation. Additionally, homogenization is essential for mitigating the element segregation in the ingot. Although it is anticipated that adding suitable particles can effectively inhibit undesired grain growth during homogenization, comprehensive investigations on this aspect are currently lacking. Therefore, TiB₂/2219Al matrix composites with varying reinforcement contents (0, 1, 3, 5 wt%) were fabricated through traditional casting followed by homogenization treatment to address these research gaps. The effects of reinforcement content and homogenization treatment on the microstructure and mechanical properties of in-situ TiB₂/2219Al composites were investigated. The results demonstrate a gradual strengthening of the refining effect with increasing particle concentration. Moreover, composites containing 3 wt% TiB₂ particles exhibit superior comprehensive mechanical properties in both as-cast and homogenized state. Additionally, potential orientation relationships are observed and calculated between undissolved Al₂Cu eutectic phase and submicron or nanometer-sized TiB₂ particles, resulting in a mixture structure with enhanced bonding strength. This mixture structure is continuously distributed along grain boundaries during solidification, forming a three-dimensional cellular network that acts as primary retarding forces for grain growth during homogenization. Furthermore, the established homogenization kinetic equations were further utilized to analyze the correlation between homogenization time and grain size, as well as the influence of homogenization temperature.

This study focuses on developing a novel multiphase stainless steel with enhanced ductility and an ultralow yield ratio achieved through solid-solution treatment. The steel exhibits remarkable mechanical properties: a tensile strength of approximately 1114 MPa, an ultralow yield ratio of 0.36, exceptional uniform elongation of approximately 17.48%, and total elongation of approximately 21.73%. The remarkable ductility of the steel can be attributed to the transformation-induced plasticity (TRIP) effect observed in the retained austenite, while its exceptional strength results from the combined effects of TRIP and the martensite phase.

The corrosion behavior of the pre-oxidized GH4169 alloy was studied after 20 h of exposure under a solid NaCl deposit film in a wet O₂ environment at 600 °C by mass-gain measurements, X-ray diffraction, scanning electron microscopy, transmission electron microscopy methods. The results indicate that the pre-oxidized GH4169 alloy undergoes serious corrosion in the corrosive condition. The preformed Cr₂O₃ layer is gradually destroyed by deposit NaCl, and the inner Nb₂O₅ layer beneath the complete outer Cr₂O₃ layer also reacts with NaCl to form NaNbO₃. The electrochemical test results testified the existence of electrochemical reactions during this corrosion process. The corrosion behavior of pre-oxidized GH4169 under a solid NaCl deposit film in a wet O₂ environment at 600 °C has been discussed in detail.

Here, the composition of TaMoNbZrTiAl refractory high entropy alloy (RHEA) is optimized by increasing Ti content to improve its mechanical property especially the ductility, through comparing two RHEAs with different Ti content. The RHEAs contain two body-centered-cubic (BCC) phases. The BCC phase in the dendritic region is rich in Ta, Mo and Nb, and the BCC phase in the interdendritic region is enriched in Zr, Ti and Al. The as-cast RHEA with a higher Ti content remains dendritic microstructures, and Ti is mainly enriched in the interdendritic region. After annealing treatment at 1300 °C for 48 h, the dendritic microstructures change into equiaxed-grain morphology, accompanied by needle-like micron precipitates at grain boundaries in the RHEA with higher Ti content. For the as-cast RHEAs, the fracture strain increases by ~ 6.6% and the uniform plastic strain increases by ~ 5.9% at the compression test due to the increase of Ti content. Our work offers a reference for the composition design of RHEAs and makes a preliminary exploration of the optimization of the microstructures and mechanical properties.