Modeling of HCP/D0_(19), D0_(19)/L1_0, BCC/B2 Phase Equilibria in a Ti-Al System by the CVM-CALPHAD Method

摘要

We applied the CVM in the octahedron and tetrahedron approximation to the calculation of α(hcp)/ α_2(Ti_3Al), α/γ(TiAl) and α_2/γ phase equilibria in the Ti-Al system. Also we analyzed the A2(bcc)/B2(TiAl) transition by the CVM in the tetrahedron approximation. The best fit to the experimentally determined α/α_2 phase boundaries was obtained for the ratio of the second nearest neighbor interaction to the first one, V~(2)/V~(1)= -0.26. We could reproduce experimentally determined α/γ and α_2/γ phase boundaries and β/B2 transition temperatures by introducing the free energy data from the thermodynamic database.