Formation process of fatigue slip bands with unique configurations of ultrafine-grained high-purity Cu fabricated by severe plastic deformation

Abstract

Fatigue-induced grain growth was observed in ultrafine-grained (UFG) metals processed by the severe plastic deformation technique, and the slip bands (SLBs) formed on coarse grains served as potential crack initiation sites. The SLBs in conventional grain-sized materials are characterized as parallel linear-like configuration along with primary slip orientation. By contrast, four typical configurations of SLBs were commonly observed in UFG materials, including granular, square lattice-like, triangular lattice-like, and parallel linear-like configurations. In the present study, stress-controlled fatigue tests were conducted on oxygen-free copper processed by equal-channel angular pressing under constant stress amplitudes. In addition, two-step block loading fatigue tests were carried out to observe the formation behavior of SLBs in a large dynamically recrystallized grain subjected to a higher cyclic stress. The objective of this study was to investigate the formation process of SLBs with a variety of configurations in UFG high-purity copper based on the microstructural evolution and the change in surface morphology because of cyclic stressing.