Intrinsic high cycle fatigue behavior of ultrafine grained pure Cu with stable structure

Ultrafine grained (UFG) materials have attracted considerable attention owing to their unique microstructure and mechanical properties. However, the easy formation of large-scale shear bands and severe grain coarsening during cyclic deformation gives rise to enormous difficulties when investigating the intrinsic fatigue behavior of UFG materials. Herein, we discuss the fabrication of an ideal model material, based on pure Cu, by friction stir processing (FSP), which exhibits equiaxed ultrafine grains, low dislocation density, and a high ratio of high-angle grain boundaries. This model material was used to investigate the intrinsic high cycle fatigue behavior of UFG material. It was found that an enhanced fatigue limit and fatigue ratio can be achieved by FSP Cu due to its uniform and stable UFG structure. Instead of traditional large-scale shear bands, protrusion was found to be the main surface damage morphology for FSP Cu during high cycle fatigue deformation, and no obvious grain coarsening was observed. Dislocation related activity also dominated, but was limited to the ultrafine grains without the formation of regular dislocation structures.