Plastic Deformation of C-Axis Sapphire Filaments.
ESSEX UNIV COLCHESTER (ENGLAND) DEPT OF PHYSICS
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The yielding and flow behavior in uniaxial, constant strain rate tensile tests of single crystal sapphire filaments oriented with the tensile axis parallel to the filament axis was studied in the temperature range from 1760C to 1875C. The existence of a strain-ageing effect leading to non-reproducible upper yield points was established. The flow stress followed a power law dependence on strain rate with stress exponents ranging from 8.50 at 1775C to 12.4 at 1875C. The apparent activation enthalpies calculated from constant temperature experiments reflect a flow stress dependence on temperature which includes both substructure and deformation mechanism temperature dependencies. The preliminary activation enthalpies calculated from differential planes are identified as the dominant slip planes with the 13 -1,1,0,1 Burgers vectors inferred from the testing geometry. Author
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