Low cycle fatigue behavior of an austenitic Fe25Mn8Al1C alloy containing grain boundary precipitates

An austenitic Fe25Mn8Al1C alloy was aged at 700 °C for 24 h. The cyclic deformation behavior of this aged alloy was then investigated at various total strain amplitudes. Furthermore, the microstructural changes induced by fatigue were examined by transmission electron microscopy. Electron microscopic observations reveal that the microstructure of the aged Fe25Mn5Al1C alloy is characterized by the presence of a high density of coarse κ-phase carbides at the austenite grain boundaries. Moreover, fine κ-phase carbides within the grains are effective barriers to slip dislocations during fatigue. As a result, planar arrays of dislocations and incomplete cell structure tend to form within the grains. Thus, an inhomogeneous distribution of a high density of intergranular carbide and the formation of planar arrays of dislocations lead to an observed two-slope behavior in the Coffin-Manson relationship. © 1995.