Deformation kinetics and constitutive relation analyses of bifurcation in work-hardening of face-centred cubic metals at cryogenic temperatures

Abstract

Abstract Crystal plasticity phenomena are described as anomalous at cryogenic temperatures if back-extrapolated trends observed at ambient temperatures are not found based on kinetic models of flow stress. The theoretical predictions are based on the Orowan relation which relates the dislocation velocity to the applied strain rate. The usual kinetic relation for plastic flow correlate the strain rate to the probability of dislocation overcoming obstacles with stress-assisted thermal activation. However at cryogenic temperatures, the obstacles can become athermal such that dislocation velocity can be approximated by a power-law relation. This change in kinetic reaction is attributed to be responsible for the observed bifurcation of work-hardening in face-centred cubic metals. The operative temperature range of these kinetic relations can be illustrated using the activation work versus temperature plot. The temperature-independent range of activation work give rise to one master curve wherein the stress-strain curve collapse into a common locus and a different master curve for the range dependent on thermal activation. The examinations of the theory and experiments which led to these deductions are elucidated.