STABILITY AND SURFACE ENERGIES OF WETTED GRAIN-BOUNDARIES IN ALUMINUM-OXIDE

The stability of a calcium-aluminum-silicate liquid film between two near-basal plane surfaces of sapphire at 1650 degrees C was studied. Samples were prepared having an average basal misorientation across the interface of 6-7 degrees about [10 $($) over bar$$ 10]. The interfaces varied in orientation from O degrees to approximate to 38 degrees to the [0001] direction. Three types of interfaces were observed: faceted, solid-liquid interfaces; low-angle grain boundaries consisting of aligned arrays of dislocations; and boundaries consisting of alternating regions of dislocations and faceted solid-liquid interfaces. The type of interface observed depended on the orientation of the interface and could be predicted by using a construction based on Wulff shapes. Because the type of interface depends on crystal alignment and interface angle, these results suggest an absolute method of determining the surface free energy of wetted boundaries.