Effect of the mode of deformation on activation volume of a material

This investigation is aimed to examine the compatibility of activation volumes for plastic deformation under tensile and compressive modes of deformation for a material. A series of tension, compression, stress relaxation (SR) and strain rate change (SRC) tests have been carried out to fulfil the objectives using a low carbon steel; in addition microstructural characterization of the steel has also been carried out. The values of activation volume (V) for plastic deformation and the athermal stresses operative at different strain levels have been estimated by thermal activation analyses using the results of SR and SRC tests. The magnitudes of effective activation volume (V*) for the steel are found to vary between 164 b3 and 245 b3 for the tensile and between 149 b3 and 358 b3 for the compressive mode of deformation. The obtained results assist to infer that: (i) the magnitudes of V* estimated by the different tests in both the modes of deformation are in reasonably good agreement, (ii) activation volume decreases with increasing stress/strain in both tensile and compressive modes of deformation. But in the former mode of deformation, V* exhibits an inflexion in its variation with stress/strain due to sharp alteration in the deformation characteristics as revealed by strain hardening analyses using modified Crussard-Jaoul method as well as due to changes in the dislocation substructure as assessed by the trend of variation of athermal stress with flow stress, and (iii) the operative deformation mechanisms in the selected steel are dislocation-dislocation intersection and cross slip.