Surface relief evolution and fatigue crack initiation in René 41 superalloy cycled at room temperature

Abstract Surface relief evolution and fatigue crack initiation of Rene 41 superalloy was studied. The material was tested in two thermodynamical states: solutionised and aged. Cylindrical specimens were cycled at total strain amplitude 0.8% at room temperature. In order to study relevant mechanisms resulting in surface relief formation and eventually fatigue crack initiation, cycling was interrupted at definite number of elapsed cycles. After each interruption, the specimen surface was observed by means of scanning electron microscopy and thin lamellae were cut out of the surface and observed by means of transmission electron microscopy. Cyclic deformation was found to localise since the first cycle, causing the formation of persistent slip bands and persistent slip markings in the form of slip steps, extrusions and later intrusions as well. Continuous cycling led to the formation of new persistent slip markings as well as widening of the already existing ones. The role of persistent slip markings in fatigue crack initiation at room temperature was found to be crucial in this superalloy. The results were thoroughly discussed in relation to theoretical models of surface relief formation.