The rate-controlling mechanism(s) during plastic deformation of polycrystalline NaCl at 0.28-0.75 TM

The plastic deformation kinetics of polycrystalline 99.9% NaCl were determined in compression at 23-532 degrees C (0.28-0.75T(M)) and a strain rate (epsilon) over dot = 8.3 x 10(-4) S-l. The rate-controlling mechanism at 0.28-0.65 T-M (sigma/mu > 3 x 10(-4)) was deduced to be the intersection of forest dislocations with a Helmholtz free energy Delta F* = 113 kJ/mol (0.16 mu b(3)). The forest dislocation obstacles become ineffective at similar to 0.65T(M). The kinetics at 0.75T(M) (sigma/mu < 3 x 10(-4)) were in accord with the Weertman-Dorn creep equation. At T < 0.5 T-M the decrease in strain hardening with strain and temperature was attributed to cross slip, leading to a brittle-to-ductile transition at 0.5 T-M. Dislocation climb was deduced to become more important at higher temperatures. The stress-strain curves were described reasonably well by the Bergstrom-Roberts dislocation multiplication model. (C) 1999 Kluwer Academic Publishers.