The effects of environment and loading waveform on fatigue crack growth in Inconel 718

The influence of environment and fatigue waveform shape on crack growth behaviour has been evaluated in a workhorse turbine disc material, Inconel 718, at 600 degrees C through an experimental programme that investigated crack growth from a notch geometry. Crack growth data are presented for a variety of stress and air pressure conditions, with specific combinations typifying model component test conditions of particular interest. The effect of waveform characteristics covering a range of loading/unloading rates and different dwell periods at peak stress was evaluated. The rates of propagation and the resultant crack profiles were found to be significantly affected by the environmental conditions through control of the dominant fracture mechanisms of transgranular and intergranular cracking. Evidence for environment controlled fatigue crack growth is presented. (C) 1999 Elsevier Science Ltd. All rights reserved.