On the free volumes of severely deformed pure Fe and Cu, similarities and differences

The present study aims to investigate the formation of free volumes in pure Fe and Cu processed by severe plastic deformation process using cold shape rolling. Transmission electron microscope for microstructural studies as well as dilatometric analyzes, radio tracer technique and density measurement for quantitative and qualitative analysis of free volumes were used. The results showed that a significant decrease in density was achieved after severe cold rolling. The results of dilatometric studies and radio tracer technique also confirmed the formation of high amount of free volumes in the severely deformed metals in comparison with the annealed metals. It was found that the relative increase of free volumes in the severely deformed Fe was higher than that of Cu. It was indicated that the high concentration of free volumes presented in the microstructure of processed metals at vacancies, dislocations, non-equilibrium grain boundaries, triple junctions, and nanovoids. In fact, the severe cold shape rolling process led to the formation of an inhomogeneous and ultrafine microstructure with the increase in free volumes in both processed Fe and Cu metals in the equivalent strain of 4.5. However, deformation mechanisms, microstructure, grain size, density reduction, and free volumes concentration as well as thermal behavior of each metal varied depending on its crystal structure and intrinsic properties.