Journal of Mining and Metallurgy, 37(3-4)B(2001)29-39. FIRST-PRINCIPLES CALCULATIONS RESULTS IN PHASE DIAGRAM CONSTRUCTION

Evaluation of lattice stabilities of metastable phases is for a long time the frequently addressed problem in thermodynamics for phase diagram calculations. Recent development of ab initio calculations makes it possible to use the total energy difference between pure element metastable structure and standard element structure for phase diagram construction also for complex intermetallic phases. The physical model of sigma-phase is proposed and tested on the Fe-Cr system, using data from literature for remaining phases. The model is based on the two sublattice model as for solid solution phase, but the structure energy difference for pure components (L1 Etotfgma-SER) is based on the results of calculations ofelectronic structure from the first principles (Full Potential Linear Augmented Plane Wave- FLAPW- method). Entropy part of Gibbs energy of elements in sigma-phase structure and of excess Gibbs energy of mixing of sigma-phase have to be still adjusted to phase equilibrium data. Extension of the model to other complex intermetallic phases is proposed