Deformation mechanisms for high-temperature creep of high yttria content stabilized zirconia single crystals

Creep of 21 mol.% yttria-stabilized zirconia single crystals has been studied between 1400 and 1800 degrees C. The creep parameters have been determined indicating a change of the controlling mechanism around 1500 degrees C. At higher temperatures recovery creep is found to be the rate controlling mechanism, with a stress exponent congruent to 3 and an activation energy congruent to 6 eV. Transition to glide controlled creep occurs below 1500 degrees C, associated with larger stress exponents (congruent to 5) and activation energies (congruent to 8.5 eV). TEM observations of the dislocation microstructure confirm this transition. The influence of the high yttria content, which is at the origin of the high creep resistance of these crystals, is discussed for each range of temperatures.