Room temperature LCF behaviour of superalloy in 718

Abstract

Low cycle fatigue (LCF) behaviour of Ni-Fe based superalloy IN 718 was studied at room temperature in the solution treated as well as aged condition. It was found to exhibit dual slope behaviour in the Coffin-Manson (C-M) relationship in both the above heat treated conditions; however, there is opposite trend in the slopes of the segments, corresponding to regimes of low and high strain amplitudes, in the two conditions. Interrupted LCF tests were carried out to investigate deformation behaviour, both at low and high strain amplitudes. These studies have revealed planar slip and cross slip as the dominant mechanisms of deformation operating at low and high strain amplitude respectively in both the conditions. Shearing of γ ∥ panicles, increasing with strain amplitude, was observed in the aged condition.