Breaking the hardness–toughness trade-off in WC–Co hardmetals: Introduction of dual-scale plate-like WC and modification of prediction models

Abstract

The hardness–toughness trade-off relationship is an essential challenge when creating high-performance WC–Co hardmetals. In this work, by combining plasma milling and low-pressure sintering, a dual-scale plate-like WC–8Co hardmetal is fabricated. The hardmetal simultaneously exhibits ultra-high strength (1701 kgf/mm2) and fracture toughness (21.77 MPa*m1/2), with bimodal grain size distributions of plate-like WC with average diameter of 1.1 μm and 1.4 μm, respectively. This breaks the normal trade-off relationship between the strength and the fracture toughness, which is because of the enhancement of crack propagation resistance owing to the synergetic effect of the plate-like WC and the bimodal grain structure. Existing models for hardness and fracture toughness prediction are invalid for WC–Co hardmetals with oriented plate-like WC grains. Modified models, based on the Lee-Gurland hardness model and the Ravichandran fracture toughness model, are developed by inducing factors R, which is the proportion of the WC(0001) plane in the indented plane, and can be determined by XRD analysis, to represent morphology features of WC. The modified models are universal and can reliably predict the hardness and fracture toughness of WC–Co hardmetals with both equiaxial and plate-like WC grains.