Abstract
The temperature dependence of fatigue crack growth in the near-threshold region of a Ni-based superalloy was investigated using constant K_<max> and ΔK decreasing test method at 800℃, 850℃, and 900℃ in a vacuum below 5.0×10^<-4> Pa and in the air. It was found that the so-called "apparent threshold" behavior, below which crack may grow upon change in loading condition, had the temperature dependence and had a peak about 850℃ in a vacuum. It was suggested that oxidation films had effects on those behaviors. Observations of fracture surfaces after those experiments were made by AFM. Fractal analysis was applied to the data and quantitative evaluations for those fracture surfaces were attempted. It was found that fractal dimensions increased as K_<max> increased.
