Production and properties of high entropy carbide based hardmetals

Different from a traditional one principle element hard phase in hardmetals, dense high entropy cobalt bonded hardmetals with two different compositions namely, (Hf-Ta-Ti-Nb-V) C-Co and (Ta-Ti-Nb-V-W) C -19.2 Vol-% Co were successfully manufactured by gas pressure sintering at 1400 °C and 100 bar Ar pressure. The microstructure of these hardmetals consists of a rigid skeletal carbide phase embedded in a tough Co binder phase. EDS mappings showed that after sintering the high entropy carbide phase didn´t dissolve and that a typical hardmetal microstructure was realized. In case of the (Hf-Ta-Ti-Nb-V) C -Co hardmetal some undissolved Ta, Hf, as well as some clustered vanadium carbide phase was found, resulting a in lowered hardness to fracture toughness ratio. Measurements of magnetic saturation polarization showed values between 57.5 % and 70 % of theoretical magnetic saturation polarization, indicating some dissolution of the carbide forming metal elements. The hardness value HV10 for (Hf-Ta-Ti-Nb-V) C-19.2 Vol-% Co was measured to be 1203 HV10 and for (Ta-Ti-Nb-V-W) C-19.2 Vol-% Co 1432 HV10.