Multiple dissociation of grain boundary dislocations in alumina ceramics

Abstract

Alumina bicrystals with a [100] 2° tilt grain boundary, including a slight twist component, were fabricated using diffusion bonding to study the change in structure due to the presence of the twist component. The resulting grain boundary structure was investigated by high-resolution transmission electron microscopy (HRTEM) and compared with that of the pure 2° tilt grain boundary. It was confirmed that the pure 2° tilt boundary was composed of basal dislocations similar to those produced by basal slip in alumina single crystals. In the case of the boundaries with a slight twist component, on the other hand, a unique dislocation structure, composed of partial dislocations in groups of five, was found, in addition to the basal dislocations. The partial dislocations in groups of five have a total edge component of 1/6[110] × 5, which compensate the given tilt angle as do the basal dislocations. In addition, they have a total screw component of 1/2[100], formed to compensate the twist angle of about 0.16°. Thus, the structure of the boundary dislocations changed noticeably due to the presence of the very low twist angle.

Acknowledgments

We thank Eiji Uehara and Jun Tohma for their technical assistance. Part of this study was financially supported by the Japan Society for the Promotion of Science.