Nondestructive Evaluation of High Temperature Low-Cycle Fatigue Damage Accumulation in Inconel 718 by Chemical Method

Abstract

In order to develop nondestructive evaluation procedure of fatigue damage in Inconel 718 which is used for components of H-II rocket engine, we investigated correlation between the fatigue life fraction and cracks and slip bands which were observed on the etched cross sectional surface of the fatigued specimens. The main results obtained are as follows. (1) The number of cracks and maximum crack depth become large with increased the fatigue life fraction N/Nf. However, maximum crack depth does not remarkably increase in early stage of the fatigue life, while cracks propagate rather fast in the latter half of the fatigue life. (2) The slip band density can be uniquely correlated with the fatigue life fraction N/Nf. The fatigue damage represented by N/Nf can be evaluated by the chemical etching technique and the damage can be evaluated from the early stage to the last stage of fatigue life.