Dislocations and twinning activated by the abrasion of Al2O3

Defects generated at the surface of single crystal Al2O3 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) over bar 0]{(1) over bar 1101}. Basal twins have platelet morphologies, with widths d(0001) = 2n*1/6[0001] and /d0001/much greater than 100 nm, aspect ratios d1010/d0001 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) over bar 0} and +/-{10 (1) over bar 0} prismatic plane abrasion results in a more uniform 1-5% deformation twin cover with basal twin penetration much greater than that for basal abrasion. Extensive microcracking along {1 (1) over bar 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 Al2O3 are discussed. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Lid. All rights reserved.