Acta Materialia最新文献

During the thermoforming of TC18 titanium alloy multi-cavity components, different deformation modes always exist and change, such as uniaxial compression (UC), shear-compression deformation (SCD), uniaxial tension (UT) and shear-tension deformation (STD). Dynamic recrystallization (DRX) of β grains occurs during the single-phase field deformation and has a great influence on the performance of components. In this study, the types and mechanisms of DRX in TC18 titanium alloy as well as transition and correlation under different deformation modes are investigated. It is found that discontinuous dynamic recrystallization (DDRX) initiates through grain boundary bulging at a low strain and dominates in different modes of deformation. Continuous dynamic recrystallization (CDRX) initiates at different strains depending on deformation modes, and the mechanisms vary, subgrain rotation within grains and lattice rotation near GBs under UC and STD, while only subgrain rotation under UT, in addition to these two mechanisms, grain fragmentation is also involved under SCD. Secondary dynamic recrystallization (SDRX) only occurs at a high strain under SCD and STD. Deformation modes lead to differences in orientation, slip and rotation of grains, further result in different dislocation density, distribution and accumulation, which contribute to the occurrence and transition of different types of DRX. Meanwhile deformation modes result in differences in the difficulty of GB migration and lattice rotation, ultimately in the initiation and degree of DDRX and CDRX. The shear stress in SCD and STD promotes the occurrence of CDRX. The present results can provide a guidance for obtaining good performance of the titanium alloy components.

The development of transition-metal-alloyed (Ti,Al)N thin films has become a common strategy to achieve optimized mechanical and thermal properties. Selection of a suitable alloying element, however, should consider the effect on Al solubility, directly influencing phase stability during the deposition. Here we use high-throughput ab initio formation enthalpy calculations to assess stability of the cubic (c) vs. hexagonal wurtzite-type (w-) phase of TM-alloyed (Ti,Al,TM)N. This compositionally-limited ab initio dataset serves to fit several machine-learning (ML) models enabling phase stability predictions over the entire compositional range. Of all the models, the linear regression using Magpie feature descriptor pre-processed by a genetic algorithm has the highest accuracy. For Ta, Nb, Mo, and W addition below ∼10 at.%, our ML model predicts enhanced stability of c-(Ti,Al,TM)N due to increased solubility of Al. Other alloying elements, especially Sc and Y from IIIB group and Hf and Zr from IVB group, decrease the cubic metastable solubility limit. In agreement with available experimental data, all transition metals except for Cr and V increase the volume of c-(Ti,Al,TM)N and w-(Ti,Al,TM)N.

Hierarchical microstructures spanning from micro-sized eutectic structure to nano-sized precipitates are promisingly engineered in lightweight Al alloys to improve the high-temperature creep resistance that is increasingly required for rapid industrial development. However, the intrinsically-brittle eutectic phase is ready to fracture upon applied loading, which, dramatically reducing room-temperature ductility and fracture toughness, greatly hampers practical applications of the creep-resistant Al alloys. Here, through the combination of Sc microalloying with sub-rapid solidification, we observe the ductilization of Al₁₁Ce₃ eutectic phase in cast heat-resistant Al-Ce-Sc alloys due to the formation of atomic-scale compositional complexity. High-concentration Sc atoms are frozen within the Al₁₁Ce₃ intermetallic phase by the sub-rapid solidification, which then assemble into unusual atomic-scale compositional dipoles with the Sc atoms enriched at one pole and the Al atoms at the opposite during subsequent heat treatment. The dispersed Sc-Al compositional dipoles induce local lattice distortions that stimulate dislocation activities, as temporally and spatially visualized by in-situ neutron diffraction tensile test and microstructural characterizations. The unexpected plastic deformation triggered in Al₁₁Ce₃ improves the deformation compatibility between the eutectic phases, enabling the sub-rapidly-solidified Al-Ce-Sc alloy to reach a room-temperature tensile elongation 3 times and fracture toughness over 8 times of its counterpart derived from traditional solidification. In addition, the sub-rapidly-solidified Al-Ce-Sc alloy exhibits an excellent creep resistance at 300 °C, achieving a tensile creep stress threshold of ∼ 70 MPa. These findings provide new perspectives on the design of ductile intermetallic phases and the development of creep-resistant Al alloys with application-level ductility.

Li₃InCl₆ (LIC) has recently emerged as a promising halide-based solid electrolyte for all-solid-state Li batteries. This study investigates the structural characteristics of LIC, with a specific focus on potential stacking faults and their impact on the properties of the solid electrolyte. A thermodynamic assessment of crystallographic stacking structures, conducted via first-principles calculations, reveals that certain variations in stacking sequences in the [010] direction relative to the previously reported reference LIC structure result in reduced crystal energy, which implies a thermodynamically more favorable new crystal structure for LIC than the extant reference structure. The efficacy of this novel crystal structure, referred to as #7–8, is evaluated against the reference structure concerning Li-ion mobility and electrochemical stability. The results demonstrate a notable enhancement in ionic conductivity while preserving a comparable electrochemical stability window. Modifications in specific stacking configurations within LIC crystals are shown to enhance Li-ion conductivity by establishing low-energy barrier pathways for Li ions in particular directions. While the mobility in other directions may decrease, this result in an overall improvement in Li-ion conductivity. The proposed crystal structure demonstrates superior thermodynamic stability compared to the conventional reference structure and is consistent with experimentally obtained X-ray diffraction data, underscoring its potential as a novel benchmark for future analyses of LIC crystal structures. Furthermore, this study suggests that two-dimensional defects, such as stacking faults, may play a crucial role in influencing the performance of halide-based solid electrolytes.