EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Friction stir processing (FSP) was applied on pure Cu to obtain a stir zone with very fine grain size with the aid of severe plastic deformation. Yet using FSP, it is impossible to obtain a uniform cross-section as far as the microstructure and mechanical properties are concerned. To reduce the effect of this limitation, in the current study, the material was processed on both sides, thus yielding a more rectangular homogenous stir zone. The influence of the processing parameters on the quality of the stir zone will be discussed based on X-ray inspection, optical metallography, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Although grain refinement was detected, the mechanical properties of the friction stir processed material are inferior to those of the parent material. The TEM study reported in the current paper revealed the existence of nano-sized grains in the FSP’ed material due to dynamic recrystallization (DRX) occurring during the processing stage. Since Both X-ray inspection and fractography showed that the FSP’ed material was defect free it is proposed that the material does not comply with the Hall-Petch relation due to lower dislocation density due to XRD occurring during FSP. The inverse Hall-Petch effect might be also considered as an assistive mechanism to mechanical propertied deterioration.