| Description |
Nearly dense, polycrystalline alumina was hot pressed with 1% and 0.2% Fe, 1% Cr, and 1/2% Ti additions. Creep experiments were conducted on the doped alumina by the constant load, four point bending test. Over a temperature range of 1375C, experiments were performed in the stress range 10 - 500 kg/cm2 and in oxygen partial pressures between 1 and 10-11 atmospheres. Steady state creep was obtained under most conditions. slightly non-viscous creep was common to most samples, except for 1% Fe samples with a 10 pm grain size tested under low stresses which were viscous. The creep rate of Cr-doped alumina was found to be independent of oxygen partial pressure. The creep rate of Fe-doped alumina decreased as oxygen partial pressure was increased, while that of Ti-doped alumina increased. Activation energies for Cr-doped alumina samples were less than those of the iron- and titanium-doped samples. The results were explained in terms of a diffusion controlled non-viscous and viscous grain boundary sliding with large contribution from volume diffusion. Models which explained the results in terms of Frenkel defects (i.e., cation vacancies and interstitials) were proposed, but distinction from oxygen boundary diffusion is not compelling. |
