Dislocations and twinning activated by the abrasion of Al 2O 3

Abstract

Defects generated at the surface of single crystal Al 2O 3 during abrasion on diamond have been analysed by high spatial resolution cross-sectional electron microscopy. Plastic deformation predominantly occurs by basal twinning and pyramidal slip 1/3〈11 2 0〉{ 1 101}. Basal twins have platelet morphologies, with widths d 0001=2 n ∗1/6[0001] and ∣ d 0001∣≪100 nm, aspect ratios d 1010/ d 0001 or d 1120/ d 0001>10, and ABCBA stacking of (0006)Al planes across twin interfaces. Basal twins and dislocations occur clustered around steps in macroscopic (0001) abraded surfaces, whereas ±{11 2 0} and ±{10 1 0} prismatic plane abrasion results in a more uniform 1–5% deformation twin cover with basal twin penetration≫that for basal abrasion. Extensive microcracking along {1 1 02} rhombohedral and (0001) twin habit planes occurs, but no widespread rhombohedral twinning, prism glide or non-basal dislocation Burgers vectors were observed. Implications for surface preparation of Al 2O 3 are discussed.