Dynamic fatigue behavior of Al2O3/TiC micro–nano-composite ceramic tool materials at ambient and high temperatures

Abstract

Dynamic fatigue behavior of Al2O3/TiC micro–nano-composite ceramic tool materials with/without metallic phase was investigated using three-point bending technique at different loading rates at ambient and high temperatures in air. When the loading rate was low, the flexural strength of two kinds of materials increased with the increase of loading rate at 23°C and 900°C, but they were more susceptible to slow crack growth at 900°C. The composite with cobalt exhibited better slow crack growth resistance than that of the composite without cobalt at ambient and high temperatures. The slow crack growth zone of specimens all originated from the tensile surface. Slow crack growth was generally a result of a stress corrosion process involving the stable growth of pre-existing defects (machining cracks on the tensile surface and residual pores in the bulk material). Crack initiation zone became larger at higher temperature, which should be attributed to the oxidation-assisted defects and the low dynamic viscosity of Co-based grain boundary phases. At 1200°C, the composite with cobalt exhibited larger plastic deformation at the loading rates of 0.08 and 0.8MPa/s, and the plastic deformation was carried out by dislocation slip and twinning. The dominated failure mechanism at the lower loading rate was ascribed to creep rather than stress-corrosion cracking.