Influence of process temperature on fatigue crack growth rate of copper in equal channel angular pressing

Abstract

The mechanical properties including Vickers hardness, tensile properties and fatigue crack growth rate and also, the microstructure of pure copper severely deformed by the ECAP in different temperatures, were studied in the present work. The equal channel angular pressing (ECAP) is a process applied to make fine grains microstructure. On the other hand, high temperature provides an opportunity for recrystallization of materials and reduces required force for ECAP at the same time. In this paper we have tried to find optimized temperature to perform ECAP effectively and reduce required force. The results indicated that the grains size can reduce from 18.2 to 2.7 µm by ECAP process. This study shows that because of the recrystallization phenomenon and reducing the effect of stress concentration and increasing the number of grain boundaries, the fatigue crack growth rate can decrease significantly. Also, it was found that the major improvement in tensile properties in all the temperature conditions and due to the applied simple shear to the copper, all the ECAPed specimens have demonstrated an enhanced hardness and resistance to fatigue crack growth. Although, these improvements decrease when the temperature increases. Finally, the SEM images of the fatigue fraction sections revealed three areas including, crack initiation, stable crack growth, and final fracture zone. It seems that the final fracture appeared to be a ductile fracture in the ECAP copper sample.