The application of strain-rate cycling data to thermally activated deformation

Abstract

The validity of using strain-rate cycling data to describe low temperature deformation in the b.c.c. alkali metal potassium, was examined using the suggestion by Li (5) that thermally activated deformation should obey the third law of thermodynamics, i.e. ΔS† = 0 at 0°K. In particular, the relations developed by Michalak (3) to separate the applied stress into its effective stress and internal stress components were demonstrated to be completely consistent with the above analysis. By the use of these relations, work hardening in polycrystalline potassium was examined and found to be strongly temperature dependent. At very low temperatures the predominant hardening mechanism appeared to be due to a decreasing mobile dislocation density with strain, leading to an increasing effective stress. At high temperatures, the internal stresses developed by the deformation built up rapidly and for strains in excess of about 5%, they provided the major contribution to the flow stress.