Pressure and strain rate dependence of dynamic recovery in NaCl

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Abstract
Crystals of NaCl have been deformed at room temperature in compression at pressures up to 10 kb at two different strain rates having a ratio of 24. At both strain rates, τIII (the stress for the onset of stage III work hardening) decreases with pressure up to a pressure of about 5 kb, whereupon, within experimental error, no further change is observed. The decrease in τIII (up to 5 kb) is more rapid at high strain rate (d In τIII/dP ≃ -0·34/kb) than at low strain rate (d In τIII/dP ≃ -0·25/kb) so the strain-rate sensitivity of τIII, (δ In τIII/δ In ∊)T,P, is decreased by about an order of magnitude between 1 atm and 5 kb.Stage III work hardening in NaCl is believed to be controlled by the thermally activated, stress-assisted, cross-slipping of screw dislocations. The decrease of τIII with pressure may be qualitatively associated with an increase in the stacking-fault energy γ, which is dependent on pressure through a strong dilatation of the lattice in the vicinity of the fault. From cross-slipping theory the dependence of the strain-rate sensitivity of τIII on pressure may be calculated. The small increase predicted is, however, in clear disagreement with the present results.