Hydrogen around dislocation has a great influence on the mechanical properties of Titanium (Ti) alloys. In this study, the diffusion of hydrogen around dislocations in alpha-Ti alloys is investigated by coupling density functional theory (DFT) calculations and the elasticity method. Initially, the attempt frequency and hopping activation energy of hydrogen atom in the alpha-Ti lattice are calculated using the DFT method under various simple strain fields, including volume strain, biaxial strain, and shear strains, within a strain range of -2%-2 %. It is observed that both volume strain and biaxial strain have the most pronounced effects on the hopping activation energy of hydrogen atom, while the attempt frequency remains relatively unaffected across different strain conditions. Subsequently, the hopping activation energy in the elastic strain field has been parameterized using an elasticity method based on elastic dipole and diaelastic polarizability. Using the elasticity method, an analysis is conducted on the effective activation energy of hydrogen atoms and their hopping tendencies in the Volterra elastic strain fields around the perfect edge and screw dislocations. The elastic strain field around screw dislocation enhances the diffusion of hydrogen atoms and simultaneously promotes their migration toward the dislocation core. In the vicinity of edge dislocation, the tensile elastic strain field enhances the diffusion of hydrogen atoms and facilitates their migration toward the dislocation core. Conversely, the compressive strain field retards the diffusion of hydrogen atoms and promotes their migration away from the dislocation core or towards regions with tensile strain.

This study investigated the formation of hydrogen-vacancy cluster at twin boundaries (TBs) in alpha-titanium and their impact on TB strength. Using first-principles calculations, it is found that a single vacancy (VA) on the {10−12} TB plane can trap up to five hydrogen atoms, while the single VA on the {10−11} TB plane can accommodate up to eight hydrogen atoms. The presence of VA weakens TBs by reducing the number of Ti-Ti bonds near the TBs. However, in the {10−12} TB with VAH5, the enhancement effect of Ti-H-Ti bonds dominates over the weakening effect of electron transfer, resulting in a slight increase in tensile strength compared to {10−12} TB with VA. On the other hand, in the {10−11} TB with VAH8, the weakening effect of electron transfer dominates, leading to a further reduction in tensile strength relative to {10−11} TB with VA. Therefore, the effect of hydrogen-vacancy cluster on the strength of twin boundaries is sensitive to the type of twin boundary. These findings provide valuable insights into the role of hydrogen in the embrittlement of alpha-titanium.

Ti‐5Al‐5V‐2Mo‐2Cr alloy is a new type of near-β Ti alloy with excellent room-temperature mechanical properties and is an ideal material for manufacturing aircraft structural parts. In this study, analysis methods such as scanning electron microscopy and electron back-scattered diffraction were used to investigate the microstructural evolution and slip of the α and β phases during room-temperature yielding. The conditions for the phase transformation between α and β phases and the β recrystallization from 600 °C to 900 °C were revealed. The β → α phase transformation occurred below 700 °C, whereas α → β phase transformation occurred above 700 °C. Meanwhile, the residual thick α phase at the grain boundary transformed into the β phase via lamellar decomposition at 800 °C. The β phase recrystallization occurred at 750 °C. The acicular α + β mixed-grain microstructure exhibited the highest yield strength. During room-temperature yielding, the {112}< 111 > slip systems dominated the slip deformation in the β phase, but a small number of {110}< 111 > slip systems were also observed. Two types of co-deformation of the α and β phases were observed: β phase slipping along the α phase interface and β phase shearing the acicular α phase. When the α and β phases were deformed together, the slip of (−112)[−11−1]β induced the activation of (11−2−2)[11−23]α, whereas the slip of (211)[1−1−1]β induced the activation of (01−10)[−2110]α.

Mg and α-Ti/Zr exhibit high plastic anisotropy. In this study, the ideal shear strength across the basal, prismatic, pyramidal I, and pyramidal II slip systems in Mg and α-Ti/Zr with and without hydrogen was computed. The findings indicate that hydrogen reduces the ideal shear strength of Mg across the basal and pyramidal II slip systems, as well as of α-Ti/Zr across all four systems. Moreover, the activation anisotropy of these slip systems was analyzed based on the dimensionless ideal shear strength. The results suggest that hydrogen increases the activation anisotropy of these slip systems in Mg, while decreasing it in α-Ti/Zr. Furthermore, the activation possibility of these slip systems in polycrystalline Mg and α-Ti/Zr subjected to uniaxial tension was analyzed by utilizing the ideal shear strength and Schmidt's law. The results reveal that hydrogen increases the plastic anisotropy of Mg/α-Zr alloy while decreasing that of α-Ti alloy.

In order to improve mechanical properties of Mg2Si/Al composites, Eu element was added to modify Mg2Si morphology, and T6 heat treatment was used to control Mg2Si morphology and precipitate strengthening phase. Microstructure and morphology of Mg2Si were observed by synchrotron X-ray tomography and TEM, and first-principles calculations were also performed to testify the effect of Eu modification. Results show that the size of primary Mg2Si particles decreases and eutectic Mg2Si phase transforms from lamellar to fibrous by Eu addition. After heat treatment, sharp angles of primary Mg2Si particles passivate, and eutectic Mg2Si dissolves and appears to be short dot-like. Meanwhile, nano-sized β" phase precipitates in the matrix. For morphology of Mg2Si with Eu modification, TEM results show that Eu impedes the growing of Mg2Si, which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg2Si {100} facet. The adsorption and suppression growing of Mg2Si transform the morphology of Mg2Si and thus improve the elongation. UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%, which improved 81% and 200% compared to the as-cast Al-15%Mg2Si composite. The strengthening mechanism mainly results from precipitation strengthening of nano-sized β" precipitates in the heat-treated composite.

Ti2AlNb-based alloys have complex phase compositions and are sensitive to temperature changes. This makes it easy to form a gradient microstructure, especially during the hot-working of large thin-walled workpieces, owing to local phase transition differences. This study prepared a layered microstructure in a Ti2AlNb-based alloy and investigated its cracking behavior and mechanism at room temperature, 750, and 930 °C. The layered microstructure comprised two layers, namely an outer large-stripped α2 + O phase and an inner B2 + acicular O phase. The layered microstructure at room temperature and 750 °C was brittle. During deformation, stripped α2 phases in the outer layer slipped with the basal slip system and cracked. The cracks propagated along the phase interface of the stripped α2/O and the B2 phases, completely peeling the strip-precipitated phases from the matrix. B2 cleavage fracture occurred in the inner layer, and both the stripped and acicular O phases in the cleavage plane peeled. The layered microstructure at 930 °C was ductile and the α2 phase in the outer layer broke, but the B2 phase filled the gap produced by breakage and restricted crack initiation. The breaking of the α2 phase promoted the dynamic recrystallization of the B2 phase and further improved its plasticity, which blunted the crack tip and effectively restrained crack propagation.

TA15 is a near‐α titanium alloy that is used extensively in the manufacturing of high‐temperature structural components and has important applications in the aerospace field. Herein, the tensile deformation behavior of a TA15 alloy with equiaxed α grains is investigated over a wide temperature range of 25–900 °C. Based on the microstructural observations and tensile testing results, the deformation behavior of the TA15 alloy is classified into four stages: 1) deformation strengthening stage at 25–550 °C; 2) α‐phase softening stage at 600–650 °C; 3) phase transition softening stage at 700–800 °C; and 4) dynamic recrystallization stage at 850–900 °C. The α→β phase transition occurs predominantly between equiaxed α grains, and the increase in β‐phase content results in further enhancement of alloy plasticity. Dynamic recrystallization occurs first at the edge of the equiaxed α grains and gradually extends into the grain interior. The size of the dimples on the fracture surface increases gradually as the temperature increases, and a large shearing and splitting area is observed at 600 °C due to α‐phase softening.

The phase transformation and microstructure in Ti-22Al-25Nb alloy are extremely complex.In this work,the morphology evolution of the O phase during the heating and cooling process was investigated by electron backscatter diffraction (EBSD) and first-principles calculations.The results show that the O→α2 phase transformation process during the heating process is as follows:spheroidization of the O phase occurs first,then the α2 phase nucleates in the spheroidized O phase,grows and replaces the O phase,completing the O→α2 phase transformation.In the meanwhile,the diffusion of Nb from Nb-poor O to Nb-rich B2 phases is a back-diffusion process.According to first-principles calculations,the driving force of the O→α2 phase transformation is the difference in the free energies of formation for the two phases(0.09eV/atom).When the Nb content is greater than 15.625 ％,the lattice distortion of the α2 phase sharply increases,and the distortion energy drives the back-diffusion of Nb.During the cooling process,the α2→O phase transformation is difficult and slow due to the difficult diffusion of Nb from the B2 to α2 phases.When holding for 60 min at 960 ℃,the coarse α2 phase gradually transforms to the O phase from the margin to the inside,forming a dispersed mixed structure of the O and α2 phases.During the B2→O transformation,the nucleation of the O phase induces a high stress region,in the range of approximately 200 nm.

The solution energy of hydrogen has been obtained by performing the first-principle calculations when the volumetric strain, biaxial strain, and shear strain are applied to the α-Zr lattice, respectively. The results show that the points of intersection between the curves of the solution energy of hydrogen at the tetrahedral interstice site and octahedral interstice site appears under the volumetric strain of 0.5% while it appears under the biaxial strain of 1.55%. The solution energy changes periodically with the shear strain directions when the shear strain is applied to different crystal planes. After the comparison of the solution energy under the volumetric strain and shear strain, the volumetric strain affects the solution energy of the hydrogen in the α-Zr lattice more significantly than the shear strain. Further, hydrogen atoms tend to gather in the tensile strain region rather than the shear strain region with the same value of strain. Hydrogen atoms accumulate at the vicinity of the screw dislocations on the prism plane could reduce the strain rate sensitivity of hcp lattice.

金属-氢系统的研究是材料领域中非常重要的一个研究方向,对其进行深入系统的研究对于解决氢脆问题、明确过渡金属催化氢机理、发展储氢材料及热氢处理技术都具有重要作用.为明确金属-氢相互作用的微观机理,本文综述了基于第一性原理的金属-氢系统的研究现状,阐述了氢对金属的晶体结构、电子结构、力学性质的影响及其氢在金属表面及内部的吸附、扩散行为,指出了现有研究的局限性,并展望了未来第一性原理在金属—氢系统研究领域中的发展方向.