EFFECTS OF LOADING WAVEFORM ON FATIGUE CRACK GROWTH AT ELEVATED TEMPERATURE IN NICKEL BASE SUPERALLOYS

摘要

The effects of loading waveform on fatigue crack growth in Alloy X at 650℃ have been examined. Fatigue crack growth behaviour was studied at frequencies from 0.001 to 2.5Hz using triangular and sawtooth waveforms. The fracture mode was found to be predominantly mixed trans/ intergranular. Further research was carried out under dwell waveforms with dwell at maximum load from 1 to 1000 s. Effects of dwell became significant with dwell times above 120 s. All tests were carried out under constant , load ratio and temperature conditions. Fatigue mechanism maps have been produced for Alloy X , showing the different modes of failure under various loading waveforms. The results have been compared with those of U720Li and Waspaloy and correlated with models by Gayda (2) and Tong & Byrne (1).