Nanofractography of Alumina by Scanning Probe Microscopy

Abstract

Observation of fracture surfaces in ceramics is useful for improving their mechanical properties. In this study, fracture surfaces of polycrystalline alumina were observed using scanning-probe microscopy (SPM) on a nanoscale, also called “nano-fractography.” The average grain size of polycrystalline alumina specimen used in this study was 4.5µm, and the fracture toughness was 3.0MPa･m-1/2. The fracture mode was found to be a mixture of intergranular and transgranular fractures. The fracture surface of intergranular fractures consisted of smooth and rough areas composed of very small steps, whose detection was impossible using scanning electron microscopy. Cleavage and non-cleavage fractures were observed in transgranular fracture grains. The fracture surface of single-crystalline alumina, which is the typical model of the transgranular fracture, was also observed by SPM. The cleavage plane of alumina macroscopically exhibited a very smooth, glass-like surface. However, sub-nano meter steps can be observed on the cleavage fracture surface and appear to be formed by plastic deformation during crack propagation because the size of the step nears that of the Burgers vector.