First-principles calculations to investigate phase stability, elastic and thermodynamic properties of TiMoNbX (X=Cr, Ta, Cr and Ta) refractory high entropy alloys

Abstract This work uses first-principles calculations to investigate the phase stability, thermophysical and mechanical properties of refractory high-entropy alloys (RHEAs) at finite temperatures. Based on plane wave quasi-potential and density functional theory, construct the structure model of a solid solution. The TiMoNbX (X = Cr, Ta, Cr and Ta) RHEAs have been determined to preserve a single BCC solid solution structure by calculations, and the equilibrium lattice parameters and elastic modulus are consistent with experimental data obtained by laser cladding, which is combined with TC4 (Ti-6Al-4V) substrate. Using the quasi-harmonic Debye-Grüneisen model, the thermophysical characteristics of three RHEAs are investigated. The Voigt-Reuss-Hill (VRH) scheme is used for calculating Young's modulus (E), bulk modulus (B), shear modulus (G), and Poisson's ratio (ν), which indicates that all three RHEAs are ductile materials. Additionally, the calculation results indicate the modulus and hardness of TiMoNbX RHEAs decrease as temperature rises. Comparing with experimental results, the nanoindentation hardness values at 300 K are higher than the calculated values. It can be attributed that the coating was strengthened by Laves phases and dislocation interaction.