Mean vs Life-Limiting Fatigue Response of a Ni-Base Superalloy, Part 1: Mechanisms (Preprint)

摘要

The fatigue variability behavior of a powder metallurgy (P/M) Nickel- base superalloy, IN100, was studied from the perspective of the prediction of useful-lifetime. We found that stress level produced separate effects on the mean-fatigue behavior and the life-limiting mechanism. In the present IN100 material, this separation of responses is suggested to be related to the different levels of heterogeneity induced by the number density and the size distribution of constituent particles vs. those of voids, and by the sequence of selection of the failure modes. Furthermore, and perhaps of greater implication, in Part II we show that the life-limiting mechanism can be described in terms of the variability in smallcrack growth from the relevant microstructural size. We also demonstrate that the above description of fatigue variability leads to a probabilistic life-prediction method based on crack growth, having the potential of significantly reducing the uncertainty in the lower-tail of fatigue variability, which is often described simply as the extrapolation of the deviation from the expected mean-response.