HIGH-TEMPERATURE HEALING OF CRACK-LIKE FLAWS IN MG-ION-IMPLANTED AND CA-ION-IMPLANTED SAPPHIRE

Controlled-geometry voids were introduced into Mg-implanted and Ca-implanted sapphire substrates using microfabrication techniques and ion beam etching, and were subsequently transferred to an internal interface bv hot-pressing. The morphological evolution of cracklike and channel-like defects in response to anneals at 1700-degrees-C was studied. The healing behavior of defects in the Ca- and Mg-ion-implanted samples differs significantly. Mg additions appear to reduce the directional dependence of the healing characteristics and thus homogenize the evolution. Destabilization of the basal plane by Ca may contribute to the rapid healing of cracks oriented parallel to the basal plane. The healing characteristics of pore channels in Ca-implanted samples indicate a strong residual energetic barrier to healing stemming from surface energy anisotropy. Despite this, defects in Ca-implanted sapphire healed more rapidly than crystallographically and geometrically identical defects in Mg-implanted sapphire. Thus, the results suggest that Ca additions increase transport rates sufficiently to more than compensate for the relatively higher energetic barriers to pore channel breakup.