Site preference of Ti and Nb in L12-ordered Co-Al-W phase and their effect on the properties of the alloy: first-principles study

Abstract

In this work, the equilibrium structure, electronic and elastic properties of L12-ordered Co-Al-W and Co-Al-W-X (X = Ti and Nb) phase were calculated, using first-principles calculations. Among six nonequivalent sites (Al1, Al2, Co3, Co4, W5, W6), Ti and Nb prefer to occupy the W6 site, since the formation enthalpy of the system is lowest when Ti and Nb occupy the W6 site. Both Ti and Nb most affect the density of states of Al atoms. Compared with the Al2 site, which is the sub-preference site of Ti and Nb, the density of states of Al atoms is higher with the addition of Ti and Nb in the W6 site, which means that the latter system is more stable. According to the bulk modulus B, shear modulus G, Young’s modulus E, hardness H V and Poisson’s ratio σ, for Co3(Al, W) alloy, the addition of Ti and Nb in the W6 site decreases its hardness but increases its ductility. This work confirms that Ti and Nb can stabilize the Co3(Al, W) alloy and have a positive effect in solving the relatively poor ductility of this alloy, which has important implications for the development of cobalt-based alloys.