Effect of grain refinement on mechanical and electrochemical properties of severely deformed pure copper through equal channel angular pressing

Abstract

Equal channel angular pressing (ECAP) not only affects the mechanical properties of pure copper but also the electrochemical behavior of copper. Thus, it would be interesting to perform a comprehensive analysis from a practical perspective. A three-dimensional (3D) simulation is carried out to reveal the strain distribution and field emission scanning electron microscopy (FESEM) is employed to investigate the microstructural evolution of copper in the course of six ECAP passes. It is found that the ECAP must be repeated enough times to bring about a significant grain refinement. This processing route will lead to observation of an ascending trend in all mechanical properties of copper except total elongation. The dislocation density shows the same ascending trend before it becomes saturated at the sixth pass. In order for copper to regain the usual homogeneity with respect to hardness, six ECAP passes are necessary. On the other hand, potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) are all employed to understand the electrochemical behavior of ECAPed copper when immersed in 0.1 M NaOH solution. After the sixth pass, copper shows its best passive and protective behavior in this solution. Furthermore, Mott–Schottky analysis indicates that although the passive film of ECAPed copper still behaves as a p-type semiconductor, it becomes less defective or less conductive as the number of applied ECAP passes increase. Consequently, the most stable passive film forms on a copper sample that has gone through six passes of ECAP.