Alloying effect on phase stability, elastic and thermodynamic properties of Nb-Ti-V-Zr high entropy alloy

The influence of alloying elements on phase stability, elastic and thermodynamic properties of random Nb-Ti-V-Zr high entropy alloys was investigated by virtual crystal approximation (VCA) based on first principles calculation. The lattice constant, elastic constant and thermal expansion coefficient of equimolar NbTiVZr agree well with other calculations and experiments, which indicates that VCA scheme is suitable for random Nb-Ti-V-Zr system. The stable crystal structure was judged by energy criterion, which shows that BCC is the most stable structure except NbxTiVZr(x ≦ 0.4) and NbTiVZrx(x ≧ 1.6). Based on BCC structure, the dependence of elastic stiffness on composition was built using CALPHAD model, which fits well with the value calculated by first principles. Furthermore, the polycrystalline elastic modulus and anisotropy were estimated. In addition, the thermodynamic properties, such as thermal expansion coefficient, as a function of component and temperature were calculated using quasi-harmonic Debyeg-Grüneisen model.