Abstract
In this paper the control of the microstructure of Ce-doped Al{sub 2}O{sub 3}/ZrO{sub 2} composites by the valence change of cerium ion is demonstrated. Two distinctively different types of microstructure, large Al{sub 2}O{sub 3} grains with intragranular ZrO{sub 2} particles and small Al{sub 2}O{sub 3} grains with intergranular ZrO{sub 2} particles, can be obtained under identical presintering processing conditions. At doping levels greater than {approximately}3 mol % with respect to ZrO{sub 2}, Ce{sup 3+} raises the alumina grain-boundary to zirconia particle mobility ratio. This causes the breakaway of grain boundary from particles and the first type of microstructure. On the other hand, Ce{sup 4+} causes no breakaway and produces a normal intergranular ZrO{sub 2} distribution. The dramatic effect of Ce{sup 3+} on the relative mobility ratio is found to be associated with fluxing of the glassy boundary phase and is likewise observed for other large trivalent cation dopants. The ZrO{sub 2} second phase acts as a scavenger for these trivalent cations, provided their solubility limit in ZrO{sub 2} is not exceeded.
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