Influence of stress wave form on fatigue strength of single crystal nickel base superalloy
Kakehi Koji
Abstract:Fatigue strength of single crystal of a nickel base superalloy (PWA1480) was studied. The stress controlled fatigue tests were performed at 700 deg. and 5 Hz 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 1000 MPa and the minimum stress was varied from zero to 1000 MPa(R = 0 - 1) at 24 and 700 degree. The fatigue tests at higher mean stress levels caused creep induced damage, which resulted in the inversion of the S-N curves at 700 degree. The results of fatigue tests at 700 deg. indicated that the fracture mechanism changed depending on mean stress and also on stress range. Key Words:single crystals, crystallographic orientation, a nickel-base superalloy, creep and fatigue strength, transition of fracture mechanisms, dislocation structure