FATIGUE BEHAVIOR OF THE NICKEL-BASED SUPERALLOY IN718 AT ELEVATED-TEMPERATURE

This paper presents the fatigue crack propagation results obtained at 600-degrees-C from CT specimens of the nickel-based superalloy IN718 used in turbine discs of aeroengines. Firstly, the influence of the stress ration on the fatigue crack growth rate was assessed for a baseline trapezoidal load waveform with a frequency of 0.25 Hz and a 1 s duration in each step. These results were then compared for three crack growth laws. The results of a preliminary study of dwell time at maximum load are also presented. The da/dN versus DELTAK results were obtained for dwell times of 2 and 5 min. A fatigue crack propagation analysis was carried out and the fatigue crack growth data were compared against the results obtained with the baseline trapezoidal load waveform. Scanning electron microscopy observations of the fatigue fracture surfaces are also presented.