Total energies of metastable and unstable structures constitute valuable data for calculation of the energy part of lattice stability difference. For complex phases they cannot be obtained by extrapolation of experimental results for alloy phases. In these cases, ab initio electronic structure calculations may substantially help in the evaluation of phase diagrams. Unfortunately, the entropic part of Gibbs energy and parameters describing the excess part of Gibbs energy of mixing necessary for phase diagram calculations by CALPHAD method in complex structures need still to be adjusted to phase equilibrium data unless they are calculated by Cluster Variation Method.
In our contribution, we summarize and generalize our recent results of application of ab initio electronic structure calculations in determination of phase equilibria in transition-metal systems containing complex intermetallic phases (Laves phase1, sigma phase2,3). The energy of formation of these phases, calculated by ab initio methods4, is compared with experiments and with the results of optimisation of existing phase equilibrium data and thermodynamic data. Some new examples of application of ab initio calculated total energy differences in the CALPHAD method are also included.
References
1. Kroupa A., Korčáková L., Houserová J., Hald J.: The improved model for the Mo-rich Laves phase and its application for modern high-Cr steels. CALPHAD XXXI, Stockholm 2001.
2. Houserová J., Friák M., Šob M., Vřešťál J.: Ab initio calculations of lattice stability of sigma-phase and phase diagram in the Cr-Fe system. Comp. Mat. Sci. 25, 562-569, (2002).
3. Houserová J., Vřešťál J., Friák M., Šob M.: Phase Diagram Calculation in Co-Cr System Using Ab Initio Determined Lattice Instability Of Sigma Phase. CALPHAD 26, 513-522, (2002).
4. Havránková J., Vřešťál J., Wang L.G., Šob M.: Ab initio analysis of energetics of sigma-phase formation in Cr-based systems. Phys.Rev.B63, 174104, (2001)