Effects of ECAE process on the fatigue crack growth rate of copper metal

Abstract

In this study, the effects of the number of passes performed by the Equal Channel Angular Extrusion as a severe plastic deformation process on copper metal's microstructure and mechanical properties, especially its resistance to fatigue crack growth, have been investigated. The experimental results show that as the number of processes passes increases, the copper metal grains become finer and as a result less stress is concentrated at the starting points of the fatigue fracture, which delays the fracture. For example, after performing 8 ECAE process passes, the threshold values of fatigue crack growth increases by 113.2% relative to the base metal. Moreover, as the grains become smaller, the number of grains and consequently the number of grain boundaries will increase and thus more obstacles will be placed in the way of crack growth. Also, the SEM images indicate that many fine and equiaxed dimples in processed copper become smaller as the number of passes increases. This shows that finer and more equiaxed grains will be obtained by repeating the ECAE process and thus repeating the occurrence of recrystallization. It was cleared that this process improves the mechanical properties of the copper other than the failure strain. However, by increasing the number of process passes, this problem can be significantly reduced.

Highlights

The fine grains considerably delay the fatigue fracture

By ECAE process, the threshold value of fatigue crack growth increases by 113.2%

All zones resulting from fatigue fracture are recognizable in fractured ECAE sample

The SEM images indicate that a ductile failure has occurred in the tensile samples