Computational Design of Alternative Binders for Sintering of Tungsten Carbide (WC) Hard Metals

Abstract There has been a long-standing effort to find alternative binders for tungsten carbide (WC) hardmetals that mitigate the safety and ethical issues related to the use of cobalt. The process of identifying new binders is often performed using conventional, experimentally based prototype-and-test approaches, which are time-consuming and expensive. Further, these efforts are mostly focused on mechanical properties with limited concern for processability, particularly through powder metallurgy routes. However, the properties of a material, including hardmetals, are path dependent and are thus determined by processing as well as composition. Here, we introduce a new computational method for finding alternative binders for the sintering of WC hardmetals that considers processing and properties simultaneously. The methodology incorporates a multi-objective optimization algorithm coupled with reduced order material design models for sintering and binder hardness. The former is based on spreading of the binder in the solid state and the sintering shrinkage rate; the latter is calculated using a generalized model for solid solution strengthening. Thermodynamic and kinetic parameters for the models are calculated using the CalPhaD (Calculation of Phase Diagram) method. Reduced order models facilitate the efficient search of compositional space enabling multiple design objectives to be optimized simultaneously. The methodology is scalable in that additional properties can be incorporated as required. The models are validated using data from the literature. Nominal design exercises using the suggested approach indicate how they can be used to guide the search for alternative binder alloys, reducing the cost and time required for the development of new materials.