Microstructural evolution of pure copper subjected to friction sliding deformation at room temperature

Samples of commercial oxygen-free high conductivity Cu (99.9% purity) have been deformed at room temperature using a rapid platen friction sliding deformation (PFSD) process, under conditions of high friction and relatively large applied load. The microstructural evolution of the surface layers during PFSD over sliding distances from 7 mm to 242 mm has been characterized and analyzed. The process results in the development of a gradient nanostructure, extending to increasing depths with increasing sliding distance. After a sliding distance of 242 mm the microstructure consists of a 15-20 µm layer of nanoscale lamellae at the top surface, with a sharp transition to a layer consisting of fine deformed grains, with a smooth transition to deformed material below this. Micro-hardness measurements of the nanoscale lamellae and fine deformed grains reveal values of ≈1.85 GPa and 1.2-1.5 GPa, respectively. Analysis of the microstructural evolution suggests that the hardening of the surface layers results in a transfer of shear strain to deeper volumes, enhancing the efficiency of the PFSD process.