Investigation of microhardness inhomogeneity of pure copper disks by HPT Processing

Processing via severe plastic deformation (SPD) to achieve ultrafine grained (UFG) materials has been an attractive research topic in last two decades. HPT process is one of the most powerful techniques to prepare ultrafine-grained (UFG) materials owing to non homogeneous deformation with large strain gradient. Also processing by HPT generally produces materials with exceptionally small grain sizes, often lying in the lower submicrometer or nanometer range, and with a high fraction of boundaries having high angles of misorientation. In HPT, a thin disc or ring is held between two anvils under high pressure and severe plastic deformation is imparted by rotating the two anvils with respect to each other. In this paper disks of pure commercial copper were processed by high pressure torsion (HPT) with several turns and applied pressures at room temperature. The Vickers microhardness tests were carried out to show the evolution of homogeneity. According to experiment results, the hardness significantly increased with first turn of HPT, whereas the increases of hardness in edges was more than in center of disks, but with increasing of turns and pressures, the microhardness became more homogeneous. Transition electron microscopy showed that by increasing the number of turns and the pressure, microstructure reached to a notable homogeneity.