Assessments of molar volumes of Co-, Ni- and Ti- related bcc and fcc phases

Abstract

In the present work, we modeled the molar volumes of the bcc phases in Co-X (X = Fe, Mo and Zr), Ni-X (X = Fe, Mo and V) and Ti-X (X = Fe, Mo, Nb, Ta and V) binary systems, as well as fcc phases in Co-X (X = Au, Fe, Ge, Hf, Ir, Mo, Nb, Ni, Os, Pd, Pt, Re, Rh, Ru, Sc, Sn, V, Zn and Zr), Ni-X (X = Al, Au, Cr, Cu, Fe, Ga, Ir, Mo, Nb, Os, Pd, Pt, Rh, Ru, Sb, Sn, Tc, Ti, V and Zn) and Ti-X (X = Au, Cu, Ni and Pd) binary systems, at room temperature and atmospheric pressure by using the CALPHAD method combined with first-principles calculations. The model parameters involve molar volumes of pure constituent elements in their stable, metastable or unstable bcc and fcc structures and excess molar volumes. Specifically, the molar volumes of the pure constituent elements in their stable or metastable bcc and fcc structures were directly adopted from the previous CALPHAD assessments or experimental measurements from the literature; for their unstable bcc and fcc structures, a new method of volume extrapolation was proposed, which avoids trial-and-error fitting. Once the molar volumes of pure constituent elements were fixed, the excess term was easily assessed according to the experimental measurements from the literature combined with the first-principles calculation results. The thus assessed model parameters can well reproduce most experimental data.