Abstract
Fatigue strength of single crystal of a nickel-base superalloy (PWA1480) was studied. The stress-controlled fatigue tests were performed at 700°C and 5Hz using triangular waveforms. In this study, two kinds of testing procedures were adopted. One is the conventional zero-tension fatigue test (R=0). Another is the procedure in which the maximum stress was held at 1000MPa and the minimum stress was varied from zero to 1000MPa (R=0-1) at 24 and 700°C. The fatigue tests at higher mean stress levels caused creep-induced damage, which resulted in the inversion of the S-N curves at 700°C. The results of fatigue tests at 700°C indicated that the fracture mechanism changed depending on mean stress and also on stress range.
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