A microstructural investigation of the mechanisms of tensile creep deformation in an Al 2O 3/SiC w composite

Abstract

The tensile creep behaviour of an SiC w (25%) reinforced alumina composite was investigated using scanning electron microscopy (SEM) and transmission electron microscopy and automatic image analysis in SEM. The creep tests were carried out in air in the ranges 1100–1300 °C and 11–67 MPa. Each creep test was performed at a constant temperature. The material had a stress exponent of about three for all temperatures and an approximate activation energy of 650 kJ mol −1. The creep resistance of this composite is poorer than that of similar composites studied earlier. Microstructural examination revealed the microstructure to be extremely inhomogeneous consisting of spherical whisker-rich clusters (20–100 μm) surrounded/separated by Al 2O 3 rich rims (10 μm). The secondary creep rate is dominated by a damage accumulation process namely cavitation and crack growth in both the SiC clusters and the Al 2O 3 rims. Final fracture seems to occur through the alumina rich regions. The lower creep resistance of this composite compared to that of similar composites is attributed primarily to the inhomogeneity of the as-received material.