The orientation dependence of dislocation slip in NaCl single crystals

Results are presented of investigations into the role of dislocation motion in deforming NaCl single crystals, using the technique of pulsed N.M.R. In particular, the spin-locking pulse sequence is used to measure T 1p, which is the spin-lattice relaxation time in the presence of a resonant r.f. magnetic field. T 1p, depends strongly on the mean free path L which is covered by the dislocations during successive jumps between obstacles in their glide plane. The mean free path is determined in crystals compressed in different directions, in which cases either the {110} or the {100} planes are primarily activated. It is shown that both the mean free path, measured as a function of strain rate and of the applied stress, and the work hardening differ remarkably for the two different primary slip planes. The magnitude of the mean free path is compared with the mean distance between dislocations in the crystal and the activation length of dislocations at obstacles, as obtained from mechanical stress relaxation experiments