Development and characterisation of novel Cr-based hardmetals strengthened by nanosized tungsten carbide

Abstract

This work highlights the promising mechanical properties and oxidation resistance achieved by novel Cr-based WC hardmetals having nanosized tungsten carbide grains, designed by combining thermodynamic calculations and experimental evaluation. The hardmetals are processed by a powder metallurgy route including mechanical milling of powders and subsequent consolidation by spark plasma sintering. The effect of the addition of different extra Fe and C contents on microstructure, mechanical properties, and oxidation resistance is fully investigated. Thus, the best mechanical performance is achieved when the formation of brittle ŋ-phases, M7C3 carbides and soft graphite is reduced or suppressed, while maintaining the nanosized WC grain size. More specifically, the Cr-based WC hardmetal with an extra 3 wt% Fe content and extra 0.5 wt% C content reaches the best combination of hardness and toughness fracture values (2219 HV30 and 8.2 MPam1/2). In addition, the oxidation resistance reached is higher than that of conventional Co-based or Ni-based WC hardmetals tested under the same conditions turning them into promising candidates for applications under aggressive oxidation environments.