Plastic deformation kinetics of fine-grained alumina

The plastic deformation kinetics of a commercial fine-grained alumina with similar to 300 ppm MgO and grain sizes from 1.4 to 2.9 mu m were determined in tension at 1475 degrees C to 1600 degrees C and strain rates from 10(-5 ) to 10(-3) s(-1), employing stress relaxation (SR) as the principal test m ode. The constants in the Weertman-Dorn (W-D) equation were determined and had the following values: A = 2.9 +/- 0.5 x 10(9), n = 2.2 +/- 0.1,p = 1.9 +/- 0.1, Q = 492 +/- 3 kJ/mole, and threshold stress sigma(0) = 0. These co nstants are in accord with grain boundary sliding (GBS) accommodated by dis location glide and climb with Al3+ ion lattice diffusion as the rate-contro lling mechanism.