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Yielding and Flow of c-Axis Sapphire Filaments


  • Presented in part at the Fall Meeting of the Basic Science, Electronics, and Nuclear Divisions of the American Ceramic Society, Philadelphia, PA, September 26, 1972 (Paper No. 42-BEN-72F).

  • R. E. Tressler was sponsored under the National Science Foundation postdoctoral program.


Yielding and flow in uniaxial, constant-strain-rate tensile tests of single-crystal sapphire filaments oriented with the tensile axis parallel to the c axis were studied between 1760° and 1875°C. The existence of a strain-aging effect leading to non-reproducible upper yield points was established. The flow stress exhibited a power-law dependence on strain rate, with stress exponents ranging from 8.50 at 1775° to 12.4 at 1875°C. The apparent activation enthalpies calculated from constant-temperature experiments reflect a dependence of flow stress on temperature which includes both substructure and deformation-mechanism temperature dependencies. The preliminary activation enthalpies calculated from differential temperature and differential strain-rate (constant-structure) experiments are comparable to the value for defect diffusion in sapphire, 80 kcal/mol. From direct evidence, the {10inline image1} planes are identified as the dominant slip planes with the 1/3 〈inline image101〉 Burgers vectors inferred from the testing geometry.

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