Activation analysis of the steady-state deformation of single- and polycrystalline sodium chloride

Single crystals and polycrystals of NaCl were deformed in compression either at constant load or at constant compression rate at temperatures above 150°C. After some transient deformation a range of steady-state deformation characterized by dynamic equilibrium of work hardening and recovery was established. The extent of transient deformation increases strongly with stress σ. For σ ≳ 2 MN/m2 the steady-state relationship between a and strain rate σ can no longer be represented by a power law with constant stress exponent: n = δ log ∊/δ log σ determined from load change or strain rate change tests increases strongly with σ. It is shown that n yields a lower boundary of the activation area of that process of thermally activated dislocation movement determining the rate of steady-state deformation. From the magnitude of the lower boundary it may be inferred that thermally activated glide of dislocations (not climb of long edge dislocations) must be rate-con trolling. No difference was observed between single- and poly-crystals of the same material. There is close qualitative agreement between steady-state deformation of NaCl and that of metals.