Effect of Non-Metallic Inclusions on Notched Low Cycle Fatigue in P/M IN100 Nickel-base Superalloy

摘要

The notched low cycle fatigue (LCF) behavior of a P/M (Powder Metallurgy) gas turbine disk superalloy (IN 100) was investigated to determine the role of inclusions, such as oxides, that are intrinsic in the process of making powder superalloys. Tests were carried out at temperatures ranging from 426℃ to 621℃ at several applied stresses. The majority of LCF failures initiated from inclusions (oxides) with minority initiation sites being grain facet in the microstructure. The locations of initiation sites were surface or subsurface, and reduced LCF life was generally associated with surface initiation at the notch root. However, surface initiation was infrequent and observed only at high stresses (i.e., in the presence of large plasticity at the notch root). The stress gradient at the notch root coupled with inclusion size determined the critical conditions for fatigue initiation. In the present paper, these failures and the associated LCF life are discussed in terms of inclusion size and its proximity to the notch root.