Deformation and fracture of WC grains and grain boundaries in a WC-Co hardmetal during microcantilever bending tests

The deformation and fracture behaviour of constituents of a WC-Co hardmetal were investigated by microcantilever bending technique. The compositions of FIB fabricated microcantilevers were: I) single grains of WC, II) WC grains of different orientations and III) the mixture of WC grains and Co phase. The crystallographic orientation of WC grains and the fracture surface of beams were studied by EBSD and SEM analyses, respectively. It was revealed that the elastic deformation depends mainly on the composition of the beams and the orientation of the WC grains. The Young's modulus of WC grains showed an orientation dependence with decreasing values from the basal (E~800 GPa) towards the prismatic orientations (E~500 GPa), which is in agreement with the theoretical predictions. The deformation behaviour of WC grains exhibited plasticity before their fracture with an average fracture strength of σ = 12.3 ± 3.8 GPa. It was found that the effect of dislocations and nanometre-sized defects (e.g. pores) plays an important role in the bending test of WC grains. Most of the WC/WC boundaries showed brittle failure with an average fracture strength of σ = 4.1 ± 2.5 GPa. It was concluded that the majority of the boundaries in the WC-Co composite are high energy WC/WC boundaries and their fracture strength is generally much lower than that of the WC grains.