Effect of a Liquid Phase on the Morphology of Grain Growth in Alumina

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Abstract
In this investigation we have studied how the presence of a liquid phase affects the grain morphology and grain growth kinetics in Al2O3at 1800°C using the growth of both matrix grains and large spherical single‐crystal seeds growing into the matrix. The growth rates of the matrix grains were found to decrease in the following order: undoped Al2O3, AI2O3with anorthite, AI2O3with anorthite and MgO, and Al2O3with MgO. Except for the samples doped with MgO alone, the matrix grains were faceted and appeared tabular in polished sections. In samples containing anorthite both with and without MgO, the single‐crystal seeds exhibit basal facets with continuous liquid films and slow growth in the 〈0001〉 relative to all other crystallographic directions. When only MgO is added, the growth of the single‐crystal seeds was not isotropic; however, no faceting was observed. We discuss how anisotropic growth rates caused by the anorthite additions can stimulate discontinuous grain growth in Al2O3.

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