The cyclic deformation response of an austenitic stainless steel was characterised in terms of its cyclic peak tensile stress properties by three stages of behaviour: a hardening stage followed by a softening stage, and finally a stable stress response stage. A series of tests were performed and interrupted at selected numbers of cycles in the different stages of mechanical response. At each interruption point, specimens were examined by transmission electron microscopy with different beam directions by means of the tilting function in order to investigate the formation and the development of dislocation structures from the as-received condition until the end of fatigue life. A new 3D representation of dislocation structure evolution during cyclic loading was proposed on the basis of the microstructural observations. The 3D representation provides a deeper insight into the development of dislocation structures in AISI316L during low cycle fatigue loading at room temperature. By investigating the dislocation evolution, the study showed that the hardening response was mainly associated with an increase of total dislocation density, whereas the softening stage was a result of the formation of dislocation-free regions. Further development of the dislocation structure into a cellular structure was responsible for the stable stress response stage.

Dislocation Structure Evolution and Its Effects on Cyclic Deformation Response of AISI316L Stainless Steel. M.S.Pham, C.Solenthaler, K.G.F.Janssens, S.R.Holdsworth: Materials Science and Engineering A, 2011, 528[7-8], 3261-9