High-Temperature Deformation of Alumina Double Bicrystals

Deformation and strength of alumina double bicrystals fabricated from verneuil-grown stock were studied as functions of temperature (1210° T 1820°C) and strain rate (0.0005 ε 0.05 min^-1). The oriented specimens had c axes parallel or perpendicular to the compressive stress axes; + a axes and c axes were matched and/or mismatched across the (1123) interfaces of the double bicrystals. Undoped ("pure") double bicrystals in which the c axes and stress axis were coincident deformed by rhombohedral twinning and, at T 1550°C, by slip. Double bicrystals containing crystal segments having c axes perpendicular to the stress axis deformed in part by basal kinking. Interfacial impurity additions of mullite or spinel thin films promoted grain-boundary fracture and sliding, whereas "pure" double bicrystals, even at stresses comparable to the ultimate strengths of single crystals in similar orientations, did not exhibit macrosliding of the grain boundary.