Phase diagram calculation in Co---Cr system using Ab initio determined lattice instability of sigma phase

The calculations of phase equilibria in the Co---Cr system were performed using the CALPHAD method on the basis of a new two-sublattices model of sigma phase. This model enables us to utilise the results of ab initio calculations of total energy differences between the sigma phase structure and the Standard Element Reference (SER) structures of pure metal at the relaxed lattice parameters (Δ0Eiσ−SER). Total energies were calculated by Full-Potential Linear Augmented Plane Waves (FLAPW) method in the General Gradient Approximation (GGA). The entropy contribution to the Gibbs energy of the pure elements in the sigma phase structure, and the excess Gibbs energy of mixing of the sigma phase were adjusted to the experimental phase equilibrium data.