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

The influence of environment and fatigue waveform shape on crack growth beh aviour has been evaluated in a workhorse turbine disc material, Inconel 718 , at 600 degrees C through an experimental programme that investigated crac k growth from a notch geometry. Crack growth data are presented for a varie ty of stress and air pressure conditions, with specific combinations typify ing model component test conditions of particular interest. The effect of w aveform characteristics covering a range of loading/unloading rates and dif ferent dwell periods at peak stress was evaluated. The rates of propagation and the resultant crack profiles were found to be significantly affected b y the environmental conditions through control of the dominant fracture mec hanisms of transgranular and intergranular cracking. Evidence for environme nt controlled fatigue crack growth is presented. (C) 1999 Elsevier Science Ltd. All rights reserved.