Place: National Institute for Materials Science / Computorial Materials Science Center CMSC, Tsukuba, Japan
Topologically close packed (TCP) phases appear in many important multi-components systems, like Ni-base superalloys and steels. However, the precipitation of these intermetallic compounds may cause problems due to their brittleness, which affects the mechanical properties of the alloy.
Computational thermodynamics is very useful to calculate phase diagrams, also in multicomponent systems, by constructing thermodynamic databases. The increased accuracy of DFT calculations and the availability of high computational power (supercomputers) make it possible to calculate the enthalpy of formation of complex phases by first principles calculations and to couple these results with the CALPHAD method. Some examples will then be shown where total energies were calculated in several binary systems for ordered configurations and used within the Bragg-Williams approximation to calculate site occupancies. Results of calculations for site occupancies and phase diagrams compare well with experiments.