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

Abstract

The plastic deformation kinetics of polycrystalline 99.9% NaCl were determined in compression at 23–532°C (0.28–0.75TM) and a strain rate ε = 8.3 × 10−4 s−1. The rate-controlling mechanism at 0.28–0.65 TM (σ/μ < 3 × 10−4) was deduced to be the intersection of forest dislocations with a Helmholtz free energy Δ F* = 113 kJ/mol (0.16 μ b3). The forest dislocation obstacles become ineffective at ∼0.65TM. The kinetics at 0.75TM (σ/μ > 3 × 10−4) were in accord with the Weertman-Dorn creep equation. At T > 0.5 TM the decrease in strain hardening with strain and temperature was attributed to cross slip, leading to a brittle-to-ductile transition at 0.5 TM. Dislocation climb was deduced to become more important at higher temperatures. The stress-strain curves were described reasonably well by the Bergström-Roberts dislocation multiplication model.