Thermally activated flow in soft and hard regions: Getting information on work hardening strain and recovery strain from rate change tests

Abstract

The investigation of thermally activated glide processes by stress reduction tests is reviewed. The tests reveal that two mechanisms of inelastic deformation are superimposed, namely dislocation glide connected with work hardening by defect storage and recovery strain related with relaxation of internal stresses and defect recovery. The coupling of the two is proposed to be modeled within the composite model. A new kind of transient testing is proposed that combines the conventional rate change test with an intermediate stress reduction. Its application to nanocrystalline Ni shows similarity of the main parameters of thermally activated dislocation glide and recovery strain found for conventional pure single and polycrystals: spacings of thermal obstacles in units of free dislocation spacing ≈ 1, back flow starting after ≈ 20 % stress reduction, similar magnitude of relative contribution and stress dependence of recovery strain. K e y w o r d s : thermally activated flow, activation area, composite model, subgrain boundaries, dislocations, recovery