Duff (ICL) Ab initio thermodynamics of ultra-high temperature ceramics; Aug 2013 – Jul 2016 and Davey (ICL) Phase stability of materials under extreme conditions; Oct 2013 – Sep 2016: A 3 year postdoctoral project (Duff) combined with a PhD project (Davey) funded by an EPSRC DTA studentship via ICL Materials Department. In combination the work is aimed at using modelling to address the poor characterisation of the thermodynamic properties and phase stabilities of UHTCs and MAX phases due to the large experimental errors associated with measuring the onset of melting. During the work, the phase diagrams of the B-C-Hf-Zr system are being re-assessed using the CALPHAD approach, within which existing experimental data is being combined with new, fully ab initio density functional theory (DFT) calculations, performed up to the melting point. Although the latter posed a significant challenge due to the strongly anharmonic lattice vibrations arising in such materials, which renders even recently developed schemes such as the UP-TILD approach too computationally inefficient for present purposes, an improved approach named TU-TILD by the team has been developed. This allows fully anharmonic DFT calculations to be performed with at least an order of magnitude improvement in efficiency. Partners in the work have included the Max-Planck-Institut für Eisenforschung and ICAMS (Ruhr-Universitat Bochum).
Bai (ICL) First order principles and DFT calculations of properties of ternary compounds in the Hf-Al-C system; Feb 2014 – Jan 2015: A wide range of ternary compounds in the Hf-Al-C system were investigated using First-Principle simulation in this 12 month project funded largely by the Chinese Government. Analysis included the crystal structure, electronic structure, compressibility, theoretical strength and elastic properties. The primary achievements have included determining that the calculated lattice parameters are consistent with those experimentally measured; none of the compounds display a band gap around the Fermi Energy, Ef, which implies they are metal-like conductors like the well-established MAX phases; elastic moduli and theoretical tensile and shear strengths have been estimated and the values obtained explained in terms of the crystal structures that these materials possess. The failure mechanism under both types of stress has also been examined in detail by analysing the density of states and electron densities.