Dynamic restoration of severely predeformed, ultrafine-grained pure Cu at 373Â K observed in situ

Microstructure changes of ultrafine-grained pure copper prepared by equal-channel angular pressing were investigated during in situ tensile testing inside a scanning electron microscope at constant total strain rate of 10−4 s−1 at 373 K (~ 0.28 Tm). After fast work hardening the flow stress saturated at an inelastic strain of 0.06. Significant local coarsening of grains was observed to start at about 2/3 of the maximum flow stress. However, these localized events did not significantly change the mean grain size up to an inelastic strain of 0.09. Surface observations showed that the coarsening was preferentially located at shear bands.