Project 12: Ab-initio calculations of bulk and interface properties at high temperatures
To achieve new levels of temperature-capability in a composite material the microstructure of the substrate and the thermal properties of the bond and top coat need to be carefully designed and tuned. The goal of this subproject is to computationally predict various high-temperature thermomechanical properties of the materials, phases and interfaces relevant for this project (i.e. refractory metal silicides and polymer-derived ceramics systems). By means of density-funtional theory calculations, harmonic and anharmonic force constants can be extracted and then used to calculate thermodynamic functions like heat capacity, vibrational entropy and free energy. Self-consistent phonon (SCPH) calculations and the Boltzmann transport equation within the relaxation-time approximation enable to determine anharmonic properties like thermal expansion and finite lattice thermal conductivity due to temperature-dependent phonon-phonon interactions. The acquired thermodynamic functions enter the phase-field modelling (project 9) and CALPHAD parametrization (project 11) in order to find the equilibrium microstructure, while the thermal conductivity and mechanical properties enter a continuum model that describes the heat transport through the multilayer composite (project 4).