Development of cyclic slip bands in UFG copper in gigacycle fatigue

Abstract

Ultrafine-grained (UFG) copper studied in this paper was produced by equal channel angular pressing (ECAP) method and tested in gigacycle fatigue region. In contrary to conventional grain size copper, the appearance of cyclic slip bands is quite rare and surface relief does not form well below the fatigue limit. The cyclic slip bands develop in regions of near-by oriented grains, where the neighbouring grains have very simmilar disorientation. Length of the cyclic slip bands substantially exceeds the average grain size of UFG Cu. No grain coarsening due to cycling was observed. Development of damage, which finally results in fatigue crack initiation, was observed below the surface relief.