Shock deformation of sapphire single crystals

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The substructures of sapphire single crystals explosively shocked at pressures of 5, 12 and 23 GPa with the (0001), (1123) or (1012) plane perpendicular to the shock wave direction have been studied with transmission electron microscopy. While there was little evidence of plastic deformation at 5 GPa, shock loading at 12 and 23 GPa introduced large numbers of uniformly distributed defects, primarily dislocations and twins. Most of the dislocations not associated with twin boundaries were basal dislocations with Burgers vectors of the types 〈1010〉 and 1 3〈1120∼> lying along specific crystallographic directions such as 〈1120〉 and 〈1010〉. A small number were non-basal dislocations. Dislocations associated with twin boundaries had 1 3〈1010〉 Burgers vectors and slipped on the basal twin planes. Changing crystallographic orientation had a significant influence on the shock-induced defect substructures, as expected from resolved shear stress considerations. Shock loading at 23 GPa with (1012) perpendicular to the shock wave direction introduced the most intense defect substructures, e.g. a volume fraction of twins of 0.19 was observed, suggesting that the plastic strain arising from the twinning shear was as large as 9%. © 1991.

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Materials Science and Engineering A