PREDICTIVE APPROACH TO THERMODYNAMIC PROPERTIES OF THE METASTABLE CR3C CARBIDE

In thermodynamic modeling of phase diagrams it is often necessary to deal with the properties of metastable compounds, which are not known from experiments. As an illustrative example, we choose the Cr3C(oP16) carbide, which is involved in the modeling of the Me3C(oP16) ("cementite") structure of the Fe-Cr-C system but is metastable in the Cr-C system. We discuss in detail the estimation of its thermodynamic properties, relying on regularities in bonding properties of 3d-transition metal carbides, and an account of the vibrational entropy through the so-called "entropy Debye temperature." Our predictions are compared with values derived in thermodynamic modeling of the Fe-Cr-C phase diagram. Relying on the present results, we perform calculations of metastable phase equilibria in the Cr-C system and use them in analyzing information about Cr3C from splat-quenching experiments.