TEMPERATURE AND STRAIN-RATE DEPENDENCE OF THE TENSILE FLOW-STRESS OF HIGH-PURITY ALPHA-IRON BELOW 250-K .1. STRESS TEMPERATURE REGIME III

Successive tensile deformations at different temperatures of high-purity alpha-iron monocrystals, combined with stress-relaxation tests, reveal that in stress/temperature regime III, i.e. below almost-equal-to 120 K, an Arrhenius equation with practically constant pre-exponential factor is valid for the temperature and strain-rate dependence of the flow stress. The experimentally determined stress dependence of the activation enthalpy follows very closely theoretical predictions of the line-tension approximation for kink-pair formation in <111> screw dislocations. The agreement between experiment and theory allows to derive numerical values for parameters which characterize kinks and dislocation structure. From these results it can be concluded that kink-pair formation, i.e., the elementary step of slip, occurs on {110} planes in this stress/temperature regime.