Small scale fracture and strength of high-entropy carbide grains during microcantilever bending experiments

The fracture behaviour of (Hf-Ta-Zr-Nb)C high-entropy carbide grains was investigated by microcantilever bending experiments, and fracture related properties (e.g. strength, toughness) were determined using linear beam theory. Microcantilevers were FIB-milled from large grains with {001} and {101} orientations and were subjected to micro-bending experiments. SEM based fractographic analysis of the broken cantilevers revealed that approximately half of them fractured at the fixing position at FIB-induced surface cracks, while the rest of the beams failed at small cracks located at submicron size pores or inclusions. In all cases, fracture occurred on the {001} cleavage plane. The fracture strength of beams fractured at the fixing position was 11.8 +/- 0.2 GPa, while the strength of the beams that failed at submicron defects was in the range of 3.8-8.9 GPa. The calculation of stress concentration in the vicinity of pores revealed that local stress field exceeded the value that induced cracking in 'defect free' beams.