抄録
Loading frequency dependence of near-threshold fatigue crack growth behavior of Ni-based conventionally cast superalloy at elevated temperatures was examined in the air and in a vacuum below 5.0×10^<-4> Pa using constant K_<max> and ΔK decreasing test method. Loading frequency was changed from 30Hz to 3Hz and vice versa, and crack growth rates at f=30Hz and 3Hz were compared. It was found that the crack growth behavior at 850℃ and 900℃ in both environments was dependent on loading frequency below the so-called "apparent threshold". Observations of fracture surfaces after those experiments were made by digital microscope and SEM. Characteristics fracture surfaces were observed.
