Elastic properties of Co-base alloys: An ab initio study

Abstract

First-principles calculations are performed to study the elastic properties of ferromagnetic Co1−xMx (M = Al, Cr, Mn, Fe, Ni, Ir; 0 ≤ x ≤ 0.2) binary alloys with a face-centered cubic (fcc) structure. The equilibrium lattice constants, magnetic properties, single-crystal and polycrystalline elastic moduli are presented as function of alloy composition. Most of alloying elements considered increase the volume of Co with exceptions of Cr and Ni, while both positive and negative changes are found in the elastic moduli by alloying. On average, Mn has the strongest effect on the elastic properties among all the alloying elements considered, while Ir shows the strongest strengthening effect and better ductility. Adding Al, Cr, Fe, Ni, and Ir is found to enhance the alloys’ ductility estimated via the bulk-to-shear modulus ratio, while adding Mn leads to a ductile-brittle transition.