The effect of alloying on the mechanical properties of TiZrNb-based refractory high entropy alloys: a first principles study

This study investigated the influence of Ta and V alloying on the mechanical properties of TiZrNb-based refractory high entropy alloys (RHEAs) though first principles with special quasi-random structure. Elastic constants, elastic anisotropy, dislocation energy factors and solid solution strengthening effects were calculated by constructing a series model of TiZrNbX (X=Ta, V, TaV) RHEAs. The calculated results showed that the introduction of Ta enhances the elastic modulus of the alloys to increase the deformation resistance, but an excess of Ta leads to a decrease in the plasticity of the alloys. The alloying of V promoted screw dislocation nucleation to give the RHEAs excellent ductility. Ta and V were together introduced to achieve both strength and plasticity due to the coupling of atomic size mismatch and shear modulus mismatch. Theoretical analyses had revealed that the introduction of Ta increases the proportion of contribution of shear modulus mismatch in the solid solution strengthening effect, but still could not replace the predominant contribution of atomic size mismatch. Analysis of the electronic structure of the (110) surface shows that Ti and Zr exhibit obvious metallic properties, while Ta and V exhibit stronger covalent properties. Furthermore, the alloying of Ta and V significantly reduced the elastic anisotropy of the RHEAs and optimized its homogeneity. The theoretical predictions of this work were consistent with the available experimental data and provided some theoretical guidance on the mechanical properties prediction of RHEAs.