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Dislocation structures in sapphire deformed by basal slip at 1200" to 15OO'C were studied by transmission electron microscopy. Long dislocation dipoles of edge character are formed by interactions of dislocations on parallel basal planes ("edgetrapping"); screw dislocations annihilate by cross-slip. The accumulation of dislocation dipoles leads to work-hardening, but the dipoles also break up into smaller loops by climb, causing recovery. Eventually a steady state of zero workhardening is reached, where the rate of accumulation of dipoles by edge-trapping is equal to their rate of annihilation by climb. From these observations, it is suggested that dislocation climb plays an important role in the deformation process for basal slip in the range 1200' to 1500'C.

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