Structure of Sapphire Bicrystal Boundaries Produced by Liquid-Phase Sintering
B Hockey, Sheldon M. Wiederhorn, J Blendell, Jong S. Lee, M K. Kang
Vitreous bonded aluminum oxide bicrystals were formed by growing oriented sapphire through polycrystalline tapes of anorthite-bonded aluminum oxide. The structure and composition of the bicrystal grain boundaries depended on the crystallographic misorientation of the sapphire crystals across the boundary and the orientation of the boundary. Dewetting was observed for tilt grain boundaries formed by rotation around the a-axis for angles of rotation less than 3. Segments of grain boundaries with normals close to the basal direction contained noticeable concentrations of adsorbed Ca and Si as measured by energy dispersive x-ray spectroscopy. Other grain boundaries consisted of dislocation arrays that were free of Ca and Si. For rotations of 7 or 12 about the a-axis, glass always wetted segments of the grain boundary containing the basal plane. Boundaries with an angle of greater than approximately 40 from the symmetric boundary plane were always dry. Boundaries that lay between the symmetric boundary plane and 40 were partially wetted consisting of segments of wetted boundaries and segments of dry grain boundaries. Ca and Si could be detected on portions of the boundary that contained no glass. Basal twist boundaries of 15 or 30 were not wetted by glass, but contained significant amounts of Ca and Si on the boundary. Most results could be explained on the basis of a combined Wulff plot construction, which predicts partially wetted grain boundaries and missing angles for unwetted grain boundaries. Results that could not be explained by the construction included growth step ledges bounded by non-equilibrium facet planes.
, Wiederhorn, S.
, Blendell, J.
, Lee, J.
and Kang, M.
Structure of Sapphire Bicrystal Boundaries Produced by Liquid-Phase Sintering, Journal of the American Ceramic Society
(Accessed June 5, 2023)