Abstract
The influence of a monotonic predeformation at room temperature on the very high cycle fatigue (VHCF) behaviour was studied on polycrystalline nickel-based superalloys (Nimonic 75 and Nimonic 80A) in three characteristic precipitation (precipitationfree, peak-aged and overaged) and different predeformation conditions. Isothermal fatigue tests were executed at temperatures up to 800 °C. With increasing intermediate temperature (400 °C–600 °C) the effect of predeformation becomes weaker which might partially be explained by the beginning of a recovery of the dislocation arrangement as well as attributed to effects not related to the strain hardened microstructure, such as the formation of oxide layers and the materials notch sensitivity for the testing conditions used given pronounced surface roughening due to the prestraining. Isothermal cyclic deformation at 800 °C revealed a pronounced decrease of cyclic lifetime for all precipitation conditions with or without a mechanical prehistory. Transmission electron microscopy was carried out in order to characterize the influence of the microstructure, the resulting dislocation slip behaviour and the relevant dislocation/particle interaction mechanism on the VHCF behaviour.
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