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Creep Resistance of the Directionally Solidified Ceramic Eutectic of Al2O3/c-ZrO2(Y2O3)

  • Jin Yi (a1), Ali S. Argon (a1) and Ali Sayir (a2)
Abstract

The creep resistance of the directionally solidified ceramic eutectic of Al2O3/c-ZrO2(Y2O3) was studied in the temperature range of 1200–1520°C both experimentally and by mechanistic dislocation models. The creep of the eutectic in its growth direction exhibits an initial transient that is attributed to stress relaxation in the c-ZrO2(Y2O3) phase, but otherwise in steady state shows many of the same characteristics of creep in sapphire single crystals with c-axis orientation. The creep strain rate of the eutectic has stress exponents in the range of 4.5–5.0 and a temperature dependence suggesting a rate mechanism governed by oxygen ion diffusion in the Al2O3. A detailed dislocation model of the creep rate indicates that much of the nano-scale encapsulated c-ZrO2(Y2O3) is too small to deform by creep so that the major contribution to the recorded creep strain is derived from the diffusion-controlled climb of pyramidal edge dislocations in the Al2O3 phase. The evidence suggests that the climbing dislocations in Al2O3 must repeatly circumvent the c-ZrO2(Y2O3) domains acting as dispersoids resulting in the stress exponents larger than 3. The creep model is in very good agreement with the experiments.

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