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 bee n determined indicating a change of the controlling mechanism around 1 500 degrees C. At higher temperatures recovery creep is found to be th e rate controlling mechanism, with a stress exponent congruent to 3 an d an activation energy congruent to 6 eV. Transition to glide controll ed creep occurs below 1500 degrees C, associated with larger stress ex ponents (congruent to 5) and activation energies (congruent to 8.5 eV) . TEM observations of the dislocation microstructure confirm this tran sition. The influence of the high yttria content, which is at the orig in of the high creep resistance of these crystals, is discussed for ea ch range of temperatures.