First-principles study of an interfacial phase diagram in the V-doped WC-Co system

We present a method of determining an interfacial phase diagram using density functional theory calculations for interface energetics. Cluster expansions based on these calculations are used in Monte Carlo simulations to obtain configurational free energies. The method is applied to study the segregation of V to the WC(0001)/Co interface and to construct the corresponding interface diagram, a ``complexion'' phase diagram. By CALPHAD-type analysis for the adjoining bulk phases, a connection with real materials is made. We find that, in equilibrium, the interface contains a thin V-rich film for a wide range of temperatures and chemical potentials of V corresponding to V additions below the (V,W)Cₓ solubility limit. The results are compared with available experimental data, and implications of the strong segregation of V for the sintering process of V-doped WC-Co are discussed.