On the possabilities to enhance the fatigue properties of ultrafine-grained metals

Abstract

Cyclic deformation behaviour of ultrafine-grained (UFG) materials processed by severe plastic deformation is reviewed in the light of possabilities to enhance the fatigue properties of UFG materaals. Based on the well-known laws from Coffin-Manson and Basquin the fatigue behaviour of UFG materaals for both, the low-cycle fatigue as well as the high-cycle fatigue regimes, are analyzed. The beneficial effects of an annealing heat treatment or a back-pressure modified equal channel angular pressing (ECAP) technique on the fatigue behaviour of UFG materials are demonstrated and critically discussed. In particular, the positive influence of an annealing heat treatment on the fatigue behaviour is explained in terms of an improved cyclic stability of the microstructure after ECAP and of an enhanced ductility. A back-pressure modified ECAP technique was used in order to achieve a ultrafine-grained, high-strength material with increased ductility, which itself is related to a combination of crystallographic slip and grain boundary sliding. The potential of enhancing the fatigue properties of UFG materials by the back-pressure ECAP technique is discussed in the context of the Coffin-Manson and Basquin relations.