Indentation Deformation and Fracture of Sapphire

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Abstract
Relatively little is known about the fundamental deformation processes in intrinsically hard, brittle materials, and even less about how these processes lead to the initiation of cracks. In this paper, transmission electron microscopy is used to study the deformation structure within Vickers indentation zones of single‐crystal sapphire with {} surface orientation. The relative misorientation of regions within these zones, as mapped by convergent‐beam kikuchi patterns, is found to be severe, indicative of shear processes operating close to the cohesive limit. Two principal types of deformation are identified, basal twinning and pyramidal slip. Incipient microcracks are observed at both the twin interfaces and the slip planes. These incipient “flaws” act as nucleation sites for the ensuing radial and lateral cracks.

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