The Electronic Origin of the Underestimated Trigonal Shear Constant of Zr1-x,Nb-x Super Alloys from First-Principles Calculations

Abstract

Zr1-x_Nb-x binary alloys are important biomaterials having high strength-to-weight ratio, plasticity, and biocompatibility. In this study, the trigonal shear constant (C-44) of Zr1-x,Nbx was found to be underestimated from the first-principles calculations. The origin of the undervalued C-44 was unraveled using the ordered supercell and the disordered special quasirandom structure methods (x= 0.25, 0.5, and 0.75). The analysis of the electronic structure revealed that the underestimation of the C-44 of Zr1-x,Nb-x is mainly caused by the underestimated C-44 of Nb and that C-44 could be increased by adopting the special quasirandom structure method. Compared to the supercell method, the special quasirandom structure method predicted not only an increase in the C-44 of Zr1-x,Nb-x with decreases in x from 0.75 to 0.5, but also a negative deviation for x= 0.25 in the trend of C44, which resulted from the softening in the body-centered cubic structure. Moreover, we found that the Young's modulus of special quasirandom structure Zr0.75Nb0.25 was in excellent agreement with that of human bones in the [010] direction. This work is of significance to the field of "super alloys" and artificial bones.