Influence of High Frequency Vibrations on the Low Cycle Fatigue Behavior of a Superalloy at Elevated Temperature

Abstract

The influence of relatively high-frequency, low-amplitude vibrations on the low-cycle fatigue (LCF) behavior and its fractographic feature for a GH36 Fe-Ni alloy at 600°C is studied. It is found that the influence is rather complicated and significant. The nature and extent of the influence depended upon the ratio of the amplitude of high-cycle to low-cycle stress range, Q. As Q approaches Qc (the critical value of Q), there is no appreciable influence on the total LCF life; as Q < Qc, it will prolong the lifetime slightly; and as Q > Qc, the fatigue life will decrease progressively. The variation of fatigue life was ascribed to the occurrence of some considerable interactions between creep, high-cycle fatigue (HCF), LCF, and environmental effect under different values of Q at elevated temperature, and the change of damage mechanism of the material. The total LCF life, especially crack propagation life, will be markedly reduced by the high-cycle vibrations when Q is much greater than Qc. Meanwhile, the mixed failure of creep, HCF, LCF, and environmental attack will gradually change into combined cycle fatigue failure with increasing Q. The fractographic analysis is in agreement with these results.