Plastic deformation mechanisms of ultrafine-grained copper in the temperature range of 4.2-300K

Main microstructural features of ultrafine-grained (UFG) polycrystalline oxygen-free copper (Cu-OF) obtained by direct and equal-channel angular hydrostatic extrusion were studied by EBSD and XRD methods. The effect of microstructure on the temperature dependences of the yield stress and strain rate sensitivity of the deforming stress was investigated using tensile and stress relaxation tests in the insufficiently studied temperature range of 4.2-300 K. Using thermal activation analysis it was established that in the range 77-200K the rate of plastic deformation is controlled by the thermally activated mechanism of crossing the forest dislocations and its empirical parameters were obtained. The experimental anomalies below 77K unaccountable by the forest crossing mechanism were explained by the inertial properties of dislocations revealed under conditions of high effective stress and low dynamic friction. The inversion of the temperature dependences of the activation volume observed above 200K was attributed to the thermally activated detachment of dislocations from local pinning centers within the grain boundaries. Published by AIP Publishing.