TRANSITION-METAL CARBIDES WITH NACL STRUCTURE

A recently reported simple method for estimating the cohesion of titanium carbide, based on bond energies, is extended to the corresponding carbides of the other group IVA and VA metals. The extra d electron in an atom of the latter produces some significant although small differences, notably a more definite decrease in cohesive energy, as x is reduced in MC(x), which is consistent with the more limited composition range of the MC phases of group VA metals. Various second order corrections to the estimated cohesive energies of TiC(x) compounds, including C-C interactions and entropic effects, enable estimates to be made of the phase limits and the primary solubility of C in Ti. An explanation is also offered for why TiC has a fcc, rather than a hcp, metal sublattice.