The role of point defect production during deformation was examined by sealing the vacancy sinks in the grain boundaries with solutes to magnify its effect upon instantaneous strain-rate changes. AA1100 aluminium sheets were thermal-mechanically treated to result in a grain size of about 25µm and in grain boundaries that were not capable of acting as efficient vacancy sinks. Tensile tests performed at 78 to 300K showed that above 195K, the pinning effect could be quantitatively analysed. A rate equation analysis for mono- and di-vacancy recovery was adopted to perform fits to the deduced change in flow stress with time after strain-rate changed from which apparent activation energies were derived. This examination indicated that the migrating species were predominantly di-vacancies. It was concluded that point-defect atmospheres had the capacity to glide in unison with mobile dislocations and hence were sensitive to the magnitude of the strain rate and temperature.

Kinetic Analysis of Dynamic Point Defect Pinning in Aluminium Initiated by Strain Rate Changes. S.Saimoto, J.Cooley, H.Larsen, C.Scholler: Philosophical Magazine, 2009, 89[10], 853-68