High-Temperature Deformation of Rutile

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Abstract
The creep of 44 rutile (TiO2) single crystals was studied as a function of stress (σ), temperature (T), ambient atmosphere, and impurity. For constant ambient and impurity in the range 1100° to 1230°C and σ=3.9–7.26 kg/mm2, the steady-state deformation rate ε̇ could be fitted quite well to ε̇=Aexp(Bσ−ΔH/kT), under conditions of constant or decreasing temperature. However, an ``hysteresis'' was observed for specimens tested with increasing temperature; ε̇ at a given temperature was irreversibly reduced after creep at a higher temperature. Nitrogen and argon atmospheres produced similar results. The ``constant'' A ranged between 1010 and 1019 for undoped specimens in N2, depending on purity. A decreased by a factor of 103 in O2, and fell to 100 and 1011 for doping with Fe and Al, in O2, respectively. B ranged: 1.0–2.2 in N2 and 0.7–1.4 in O2. ΔH ranged: 5.7–7.7 eV in N2, 4.0–7.5 eV in O2, 2.3 and 5.8 eV for doping with Fe and Al, in O2, respectively. In all cases, less than 10% scatter was observed for tests with the same atmosphere and purity. Significant changes in activation energy as a function of stress were found only for the highest-purity specimens (about 30-ppm cation impurities); in these crystals ΔH increased abruptly by ∼2 eV at a stress between 3.9 and 4.5 kg/mm2, with accompanying changes in A and B.