Microstructural stability of Cu processed by different routes of severe plastic deformation

The thermal stability of ultrafine-grained (UFG) microstructure in Cu processed by different routes of severe plastic deformation (SPD) was studied at both high and room temperatures (RT). It was found that the microstructures produced by multi-directional forging or twist extrusion were more stable than those obtained by equal-channel angular pressing (ECAP) or high-pressure torsion (HPT). During storage of the ECAP-processed specimen at RT for 4 years the vacancy concentration reduced significantly while the dislocation density and the crystallite size remained unchanged. In the case of the HPT-processed sample both grain-growth and reduction of the dislocation density were observed.