Abstract
Alumina bicrystals were made by joining two mirror-polished single crystals at 2173K in order to obtain symmetrical and asymmetrical grain boundaries of alumina. Their interfacial fracture toughness values were estimated by single edge V-notched plate tension method. The fracture toughness values of the symmetrical tilt boundaries were almost the same as those of the asymmetrical tilt boundaries, showing a concave curve as the tilt angle increased The fracture toughness values of symmetrical twist boundaries changed on another concave curve as the twist angle increased. There was also no significant difference in the fracture toughness between symmetrical and asymmetrical twist boundaries.
