Epitaxial Grain Growth During Splat Cooling of Alumina Droplets Produced by Atmospheric Plasma Spraying

Alumina splats were deposited on the polished single crystal alumina substrates with two different crystalline facet orientations of [001] and [110] by atmospheric plasma spraying (APS) at a substrate temperature of 900°C to examine the epitaxy during splat cooling. The cross-sectional samples for high resolution transmission electron microscopy examination was prepared by focused ion beam assisted scanning electron microscopy (FIB-SEM). The results showed that the whole splat with a thickness ranging from ~500 to ~1000nm exhibited the same crystalline structure as the substrate. Moreover, the splat deposited on the single crystalline alumina substrates exhibited exactly the same orientation as the substrate. The results evidently indicate that the epitaxial grain growth occurs after alumina droplets impact on single crystal alumina substrate. The present results suggest that the crystalline structure of alumina deposit formed by plasma spraying can be possibly controlled by substrate seed.