High temperature deformation Behavior of [0001] symmetrical tilt Σ7 and Σ21 grain boundaries in alumina bicrystals

High temperature deformation behavior of [0001] symmetrical tilt grain boundaries of Al2O3 was investigated by using bicrystals. Four kinds of the grain boundaries Sigma7/{4510}, Sigma21/{4510}, Sigma7/{2310} and Sigma21/{2310} were selected in the present study, and compressive mechanical tests were performed at 1450degreesC in air to investigate the sliding behavior of the respective boundaries. It was found that, stresses readily increased with increasing strains for all specimens during compression tests, but the bicrystals showed abrupt sliding along the grain boundary planes to fracture. Among the boundaries studied, Sigma7/{4510} exhibited the highest resistance to the grain boundary sliding. The other boundaries showed similar sliding resistance, and yet the stress and strain values at their failure were much smaller than those of Sigma7/{4510}. In order to understand the mechanism of the sliding behavior of the respective boundaries, the grain boundary core structures and their atomic densities were examined, based on the structure models obtained in our previous studies. It was found that Sigma7/{4510} having the highest sliding resistance showed a larger atomic density at the core, as compared to the others. Therefore, the observed sliding resistance of the boundaries is closely related to the detailed atomic structures at the grain boundary cores.