•The dissolution of H in V15M is affected by the elastic and electronic properties.•The elastic effect is the main factor that affects the dissolution of H in V15M.•Add a smaller atomic size elements reduce the H solubility in vanadium.•Additions of Al, Ti and Nb improve the diffusion coefficient of H in vanadium.Vanadium-based alloys are considered to be one of the most promising hydrogen separation membranes due to their high hydrogen permeability. In this study, we investigate the dissolution and diffusion behaviors of hydrogen in vanadium-based binary alloys, V15M (where M = Al, Ti, Cr, Fe, Ni and Nb) alloys, using first-principles method based on density functional theory. The dissolution of hydrogen in V15M alloys is affected by both the elastic and electronic properties, but the elastic effect is the main factor. The H solution energies in the alloys follow the sequence: VTi < VNb < VAl < VCr < VNi < VFe, and a smaller atom size increase the H solution energy. Therefore, the addition of alloying elements with smaller atomic sizes can reduce the solubility of hydrogen in vanadium and inhibit hydrogen embrittlement. For hydrogen diffusion, alloying elements Al, Ti and Nb can be good candidates because they have a higher diffusion coefficient. The VTi alloy has the highest hydrogen permeability, but will have serious hydrogen embrittlement due to the increased H solubility.Download high-res image (120KB)Download full-size image

•The double-island phenomenon is studied at atomic scale by binary phase field crystal.•The morphological evolution of epitaxial layer depends on signs of misfit strains.•Misfit strains with different signs have important influences on concentration field and density field.•Free energy of systems under different misfit strains has similar variational trend.Influences of misfit strains with different signs on liquid phase heteroepitaxial growth are studied by binary phase field crystal model. It is amazing to find that double islands are formed because of lateral and vertical separation. The morphological evolution of epitaxial layer depends on signs of misfit strains. The maximum atomic layer thickness of double islands under negative misfit strain is larger than that of under positive misfit strain at the same evolutional time, and size differences between light and dark islands is much smaller under negative misfit strain than that of under positive misfit strain. In addition, concentration field and density field approximately have similar variational law along x direction under the same misfit strain but show opposite variational trend under misfit strains with different signs. Generally, free energy of epitaxial growth systems keeps similar variational trend under misfit strains with different signs.Download high-res image (171KB)Download full-size image

•The liquid phase heteroepitaxial growth is studied at atomic scale by binary phase field crystal.•Atomic sizes have different influences on phase separation under positive and negative misfit strain.•Under the condition of different mobility, atoms with greater mobility accumulate at the film surface.•The epitaxial layer exhibits double islands phenomenon: light and dark islands.The binary phase field crystal (PFC) model is employed to investigate influences of atomic sizes and mobility differences on the liquid phase heteroepitaxial. It was found that large size atoms are driven toward regions of tensile stress which correspond to peaks in a compressively strained film but to valleys in a film with tensile strain. Small size atoms are on the contrary in contrast for large size atoms. Due to the existence of vertical separation and lateral separation resulting from atomic size differences, the epitaxial layer exhibits double-island phenomenon: light and dark islands. In the presence of different mobilities, atoms with greater mobility accumulate at the film surface. And in the process of epitaxial growth, there are misfit dislocations nucleating in valleys where the strain is highest.

•The liquid phase epitaxial growth is studied at atomic scale by binary phase field crystal.•The morphology of epitaxial films undergoes several transitions during epitaxial growth.•There exists preferential regions while islands grow on both sides of substrate.•Substrate vicinal angles have important impacts on the islands.The liquid phase heteroepitaxial growth on predefined crystalline substrate is studied with binary phase field crystal (PFC) model. The purpose of this paper focuses on changes of the morphology of epitaxial films, influences of substrate vicinal angles on epitaxial growth, characteristics of islands growth on both sides of the substrate as well. It is found that the morphology of epitaxial films undergoes the following transitions: layer-by-layer growth, islands formation, mismatch dislocations nucleation and climb towards the film-substrate interface. Meanwhile, the density of steps and islands has obviously direct ratio relations with the vicinal angles. Also, preferential regions are found when islands grow on both sides of the substrate. For thinner substrate, the arrangement of islands is more orderly and the appearance of preferential growth is more obvious than that of thicker substrate. Also, the existing of preferential regions is much more valid for small substrate vicinal angles in contrast for big substrate vicinal angles.

•The thermal properties of SrTiO3 and SrO(SrTiO3)n (n=1,2) are analyzed.•Thermal expansion coefficient of Sr3Ti2O7 increase is the fastest with increasing temperature.•Disparities in CP and CV, BS and BT of Sr3Ti2O7 increase the most quickly with increasing temperature.•The bulk modulus and Debye temperature increase with the decrease in SrO/SrTiO3 ratio at 0 K.•The thermal properties of these three compounds from 0 GPa to 16 GPa and at 300 K are analyzed.The thermal properties of SrTiO3 and SrO(SrTiO3)n (n=1,2) with layered perovskite structure are analyzed using the Debye–Grüneisen model combined with ab initio calculations. The thermal expansion coefficient, specific heat at constant pressure CP and specific heat at constant volume CV, adiabatic bulk modulus BS and isothermal bulk modulus BT, entropy, and Debye temperature are investigated. At temperatures higher than 550 °C, the thermal expansion coefficient and the discrepancies between CP and CV, as well as that between BS and BT, of Sr3Ti2O7 increase the fastest as the temperature rises, followed by those of Sr2TiO4, and those of SrTiO3 increase the slowest. The bulk module and Debye temperature of Sr2TiO4, Sr3Ti2O7, and SrTiO3 increase with decreasing SrO/SrTiO3 ratio at 0 K. With increasing temperature, however, the bulk modulus and Debye temperature of Sr3Ti2O7 both rapidly decrease and even fall below those of Sr2TiO4 when the temperature is higher than specific values. We also analyzed the thermal properties of these three compounds in the pressure range from 0 GPa to 16 GPa at 300 K.

•Elastic constants, modulus and anisotropy of SrO(SrTiO3)n (n=1,2) and SrTiO3 are calculated.•Hardness decreases with decreasing SrTiO3/SrO ratio for SrO(SrTiO3)n (n=1,2) and SrTiO3.•Elastic constants of SrO(SrTiO3)n (n=1,2) as a function of volume(pressure) is studied.•The volume threshold of Sr2TiO4 and Sr3Ti2O7 when the system is in stable state is obtained.Layered perovskite SrO(SrTiO3)n (n=1,2) and SrTiO3 were analyzed using the density functional theory within a generalized gradient approximation. The elastic properties of SrTiO3, Sr2TiO4, and Sr3Ti2O7, including the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and elastic anisotropy ratios, were investigated. Results show that hardness decreases with decreasing SrTiO3/SrO ratio. Except for C66, all elastic constants tend to decrease with decreasing volume. When the Sr2TiO4 and Sr3Ti2O7 volumes are higher than 15.8 and 16.9 Å3/atom (or lower than 10.4 and 10.1 Å3/atom), respectively, C33 (or C66) decreases to zero and the structure becomes unstable. Phase transition and shear generation along the YZ direction occur under high-positive pressure (low volume) and high-negative pressure (high volume) conditions, respectively.

The formation and evolution of deformation texture in polycrystalline materials are studied by phase-field dynamic model. In addition, the driving force of texture evolution is also discussed. In this model, grains with different orientation are defined by a set of continuous non-conserved order parameter fields. Simulation results show that grains with preferred orientation grow at the expense of those with unfavorable orientations. It is more important that, elastic potential rather than elastic energy plays a crucial role in the evolution of texture whether the polycrystalline system is subjected to uniaxial stress or shear stress.

The microscopic phase-field dynamic model is employed to study the pre-precipitation process of Ni–Al–V alloy. Our computer simulation results show that there exists pre-precipitated phase with L10 structure before L12 phase formed, temperature and elastic strain energy play significant effect on the pre-precipitated phase with L10 structure. The elastic strain energy can induce the formation of L10 pre-precipitated phase. Under the same temperature, the greater the elastic strain energy is, the easier L10 pre-precipitated phase will form; under the same elastic strain energy, with the temperature increasing, the incubation period and existent time of L10 pre-precipitate phase are prolonged, the number of L10 precipitated phase also increases, and the formation of the L12 phase are delayed.Highlights► There exists pre-precipitated phase with L10 structure before L12 phase formed. ► The elastic strain energy can induce the formation of L10 pre-precipitated phase. ► Increasing the temperature, the incubation period of L10 pre-precipitate phase are prolonged. ► The pre-precipitated phase affects the precipitation process of L12-Ni3Al.

Based on the microscopic phase-field dynamic model and the microelasticity theory, the coarsening behavior of L12 and DO22 phases in Ni75CrxAl25−x alloy was simulated. The results show that the initial irregular shaped, randomly distributed L12 and DO22 phases are gradually transformed into cuboidal shape with round corner, regularly aligned along directions [100] and [001], and highly preferential selected microstructure is formed during the later stage of precipitation. The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics, and there is no linear relationship between the cube of the average size of precipitates and the aging time, which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner. The coarsening processes of L12 and DO22 phases are retarded in elastically constrained system. In the concurrent system of L12 and DO22 phases, there are two types of coarsening modes: the migration of antiphase domain boundaries and the interphase Ostwald ripening.