Study of phase equilibria in the Nb-Ti-Al system theoretical study: CVM calculation of the phase diagram of bcc Nb-Ti-Al

The cluster variation method (CVM) in the irregular tetrahedron approximation has been used to calculate the temperature and composition limits of the ordered-cubic-centered B2 phase field in the Nb-Ti-Al system. Results show that this B2 domain is large and particularly extended toward the Nb-rich compositions. The order-disorder B2 → A2 transition temperature and the occupation probabilities of sites of the B2 phase are strongly dependent on composition that is in agreement with experimental results [98Cha].