Phase stability and mechanical properties of sigma phase in Co-Mo system by first principles calculations

First principles calculations are applied to study the phase stability and mechanical properties of sigma phase in cobalt-molybdenum (Co-Mo) system. Formation enthalpies have been used for the evaluation of stability, and are compared among the selected configurations. Based on the most energetically stable configurations, a ground-state line is sketched out for the Co-Mo sigma phase. Magnetic effects and electronic structures have also been explored to explain the compositional dependence of phase stability. The elastic constants and polycrystalline elastic moduli are calculated and exhibit similar compositional trends as the formation enthalpies. A significant degree of elastic anisotropy is predicted, which can shed light on the brittle nature and rapid crack propagation of sigma phase. (C) 2014 Elsevier B.V. All rights reserved.