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Precipitation processes in two titanium-doped aluminas (0.14 and 0.60 cation % titanium) have been examined using a variety of analytical electron microscopy techniques. The results strongly suggest that, for an ageing temperature of 1573 K, rutile is the only precipitate formed in the 0.14 cation % titanium material. However, evidence for the precipitation of both rutile and ?-Al2TiO5 (the latter at triple junctions) was obtained in the 0.60 cation % titanium sample.

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.