Effect of γ′ size on room temperature low cycle fatigue behaviour of a nickel base superalloy

The results of a study on the effect of gamma' particle size on the room temperature (23 degrees C) low cycle fatigue (LCF) behaviour of a Ni base superalloy, Nimonic 90, is reported. The gamma' particle sizes were estimated from transmission electron micrographs. Ranges of particle sizes corresponding to underaged, peak aged, and overaged conditions were identified by examining the age hardening response curve. The solutionised samples had longer LCF lives compared with the aged alloys. Coffin-Manson and cyclic stress-strain plots showed bilinearity at a plastic strain amplitude of around 0.4% in the solutionised, underaged and peak aged conditions. The observed bilinearity could be attributed to a change in the deformation mode from single slip to multiple slip. The cyclic stress response showed relatively stable behaviour for the peak aged and the overaged specimens compared with the underaged and the solution treated specimens. MST/3854.