First-principles study on structural stability, electronic structure and mechanical properties of VB group transition metal tungsten alloys W-TM (TM=V, Nb, Ta)

The engineering design of tungsten and its alloys as plasma-oriented components has been proposed and practised as an effective solution to the key problem of the interaction between plasma and wall materials in Tokamak experiments. However, it is still worth exploring the internal mechanism and the influence of mechanical properties after the transition metals (TM) of the same group form alloy with tungsten (W). In this work, the structural stability, electronic structure, mechanical stability and Debye temperature of W-TM (TM=V, Nb, Ta) alloy were investigated by first principles based on density functional theory. The lattice constant, formation energy and cohesion energy of W-TM alloy were calculated. The W-TM alloy remains a bcc lattice, and all structures are energy stable. Using the optimized lattice, the elastic constants are calculated, and the elastic modulus and other mechanical parameters are derived. It is found that most of the mechanical properties of WTM are lower than those of tungsten, especially W-Nb alloy, but B/G and Poisson's ratio prove that W-TM alloy has better ductility. The calculated melting point Debye temperature proves that the alloy has no significant change from pure tungsten and can still maintain good thermal stability. The metallicity of tungsten can be enhanced by doping with VB group transition metals. Among them, W-Ta alloy can effectively improve the ductility of the material without causing serious decline in other mechanical properties. The research results can provide a reference for the selection of plasma materials for fusion reactor design.