Cyclic stress–strain response and low-cycle fatigue damage in ultrafine grained copper

We report on the fatigue behavior of ultrafine grained (UFG) copper obtained by equal channel angular extrusion (ECAE). Cyclic stress–strain response and fatigue life data were determined in fatigue tests conducted in the low-cycle fatigue (LCF) regime. The early stages of the fatigue process were examined in a scanning electron microscope equipped with a small-scale load frame that allowed for in situ fatigue observations. AE route 16E gives superior fatigue performances as it provides for stable cyclic stress–strain response and more homogeneous plastic deformation than routes that are composed of lower number of ECAE passes. Still, the in situ fatigue tests indicated that fatigue damage occurs on a very localized scale, and thus, additional strengthening mechanisms need to be exploited to obtain UFG materials that display enhanced microstructural stability.