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CALPHAD phase diagrams from DFT calculations
- Date: 14.09.2010
- Place: Ψk (Psi-k) Conference 2010, Berlin, Germany
The CALPHAD (CALculation of PHAse Diagrams) method relies on Gibbs energy databases. When only limited experimental data is available for the Gibbs energy parameterization, the predictive power of the CALPHAD calculations will also be limited. For example, for the calculation of the phase transformation kinetics within phase field simulations not only the thermodynamic equilibrium data is required but information on metastable phases is also necessary. Such information is difficult to obtain directly from experiment. Ab initio calculations may supplement experimental databases as they comprise metastable phases and arbitrary chemical compositions. In our work we demonstrate how density functional theory (DFT) calculations of the heat of formation may be used within the CALPHAD methodology for the calculation of prototypical phase diagrams. We present simulations for two systems, ReW and FeB. For both systems we calculate the heat of formation for an extensive set of structures using DFT calculations and employ the total energies in CALPHAD calculations in order to determine the corresponding phase diagrams. We account for the configurational entropy within the Bragg Williams approximation and neglect the phenomenological excess term that is commonly used in CALPHAD as well as the contribution of phonons and electronic excitations to the free energy. According to our calculations the complex intermetallic phases in ReW are stabilized by the configurational entropy. For FeB, we calculate metastable and stable phase diagrams and predict a new stable phase.