Microstructural Features and Dislocations on Thermally Etched Sapphire Surfaces

Abstract
Basal‐, prism‐, and rhombohedral‐plane specimens cut and polished from flame‐grown sapphire boules developed fine surface textures during heat‐treatment in the range 1700° to 1900°C. Microscopic examinations of such surfaces revealed low‐angle grain boundaries, dislocations, and other crystal imperfections. Thermally etched textures apparently were generated by three overlapping processes, namely annealing, etching, and decoration. Thermal etching gave evidence of high‐temperature relaxation of residual strain energy introduced at low temperature (analogous to cold work in metals), including that introduced by fracture, microindentation, and cutting and polishing during surface preparation.

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