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 L1 2 -ordered Co-Al-W and Co-Al-W-X (X = Ti and Nb) phase were calculated, using first-principles calculations. Among six nonequivalent sites (Al 1 , Al 2 , Co 3 , Co 4 , W 5 , W 6 ), Ti and Nb prefer to occupy the W 6 site, since the formation enthalpy of the system is lowest when Ti and Nb occupy the W 6 site. Both Ti and Nb most affect the density of states of Al atoms. Compared with the Al 2 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 W 6 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 Co 3 (Al, W) alloy, the addition of Ti and Nb in the W 6 site decreases its hardness but increases its ductility. This work confirms that Ti and Nb can stabilize the Co 3 (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.