Deformation dynamics of pore-free Ti4+-doped and pure c-axis sapphire crystals

Single crystal alumina filaments undoped and Ti⁴⁺-doped, having the c-axis within 2° of the filament axis were plastically strained in constant strain-rate tensile experiments. The results of differential strain-rate and differential temperature tests were used to calculate the stress exponents in the strain-rate equation, the activation volumes, and the activation enthalpies. The relatively high values of the stress-exponents (6 to 7), the variations of the activation enthalpy with stress and temperature, and the magnitudes of the strain-independent activation volumes suggest overcoming the Peierls-Nabarro stress as the rate-limiting mechanism for plastic deformation of the alumina crystals. The microscopic observations of the deformed specimens are consistent with slip on the {10¯11} <¯1101> pyramidal system as reported in previous investigations of similar materials.