Effect of the LCF loading cycle characteristics on the fatigue life of INCONEL 718 at high temperature

A series of both stress-controlled and strain-controlled low cycle fatigue tests were conducted on alloy Inconel 718 to investigate the impact of various parameters on the behaviour of the material. Namely, focus was placed on the influence of major parameters such as the cycle frequency, the strain/stress rate, the holding time at various stress levels, the stress relaxation and the fatigue stress ratio. A detailed characterisation of the fatigue-induced rupture surfaces was performed to analyse the role of the alloy microstructure on the mode of crack propagation. In order to account for the time dependent effect of the mechanical response of the alloy, the Portevin-Le Châtelier effect and the oxidation behaviour of the material are discussed. Results are analysed, in terms of Manson-Coffin plots, to discriminate the relative impact of the various tested parameters on the stress/strain response and the fatigue life of the material. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.