Screen the elastic and thermodynamic properties of MAX solid solution using DFT procedue: Case study on (Ti1-xVx)2AlC

Abstract

As one of Mn+1AXn (MAX) family, where M is an early transition metal, A is an A-group element, and X is either C or N and n = 1, 2, and 3, Ti2AlC is a promising candidate material for nuclear energy industry due to its unique features such as elastically stiff, good electrical conductivity, high thermal conductivity and excellent resistance to high temperature oxidation and corrosion. However, the mechanical and thermal properties of Ti2AlC compound are expected to be improved. For the first time, the effect of V content on the structural, elastic, electronic and thermodynamic properties of the (Ti1-xVx)2AlC (x = 0, 0.25, 0.50, 0.75 and 1.00) solid solutions was examined systematically and their compression behavior under 50 GPa was studied using density functional theory (DFT). The optimized lattice constants agree well with the experimental values and decrease with the increase of V content. The (Ti1-xVx)2AlC solid solutions are compressible along both a and c directions in the pressure range of 0–50 GPa. Calculated elastic constants verified mechanical stability under 50 GPa. The constant C44, directly related to the valence electron concentration, is found to increase with increasing V content. The bulk modulus, shear modulus, Young's modulus and Vickers hardness are found to reach a significant maximum value respectively when V content is 75%, and the reason is studied. The shear anisotropy factors show that (Ti1-xVx)2AlC compounds containing Ti and V are more anisotropic than Ti2AlC, and they have a tendency towards improved ductility. The metallic behaviors of (Ti1-xVx)2AlC solid solutions are confirmed by analyzing the electronic band structures and density of states. The thermal properties imply that the (Ti0.25V0.75)2AlC is expected to be more thermally conductive due to its highest Debye temperature of 771K of the five compounds. In addition, the bulk modulus, shear modulus, Young's modulus and Debye temperature increase with the increase of pressure under 50 GPa. The results reveal that the mechanical properties of Ti2AlC are improved much better than the thermal properties by the inclusion of V. Especially, the (Ti0.25V0.75)2AlC MAX phase in (Ti1-xVx)2AlC solid solutions is probably the most suitable candidate material for mechanical and thermal applications at high temperature.