TOWARD THE GENERATION OF AN ENGINEERING-TYPE THERMODYNAMIC DATABASE FOR ALUMINUM HEAT TREATABLE ALLOYS BASED ON FULLY SELF-CONSISTENT DFT-BASED THERMODYNAMIC PROPERTIES

Quasiharmonic approximation, Self consistent thermodynamic modelling Aluminum-based heat treatable alloys are of prime importance for several highly technological aerospace applications. They present superior specific mechanical properties that are modulated by the controlled precipitation of stable/meta-stable phases via specific heat treatments. Being able to predict the phases that are precipitating under equilibrium or near-equilibrium conditions is a first step toward the optimization of their mechanical performance. The thermodynamic properties of these metastable phases are experimentally difficult to assess; sets of thermo-physical data are often lacking for those phases. Fortunately, it is nowadays possible to estimate thermodynamic properties of metastable compounds or solutions using atomistic simulations based on the Density Functional Theory (DFT). Accurate ground-state properties such as the OK enthalpy of formation can be easily evaluated from DFT calculations for large sets of unary, binary and ternary ordered compounds with various crystallography structures (L12, D022, D023 and FCC). Other thermodynamic properties such as the heat capacity at constant pressure can be estimated from these DFT ground-state calculations by applying a phonon-based treatment for the effect of temperature (i.e. the quantification of the thermal vibrational kinetic energy) using approaches like the Quasi Harmonic Approximation method (QHA). The QHA relies on the parameterization of an equation of state (EOS) using the internal energy-deformation curves from DFT calculations. The estimation of the temperature dependence of several thermodynamic properties (such as heat capacities and thermal expansivities) and elastic properties (Cll, C12, C44) can be obtained from this approach. It has been recently shown that the QHA is not necessarily self-consistent as it can violate some Maxwell's relations [1, 2, 3]. It was also highlighted that there is generally no systematic way of preserving self-consistency in the literature when applying the QHA. Moreover, the Gibbs free energy of solids predicted with the QHA is most of the time overestimated (few kJ/mol at melting) which could considerably impact phase equilibrium calculations. The aim of this work is to alleviate the inconsistencies of the QHA method to obtain sets of fully self-consistent thermo-physical properties of Al-based binary and ternary ordered compounds. To do so, an iterative self-consistent scheme usin