Effect of frequency and orientation on fatigue crack growth behavior of forged turbine disc of IN 718 superalloy

The fatigue crack growth behavior of forged turbine disc of IN 718 superalloy in radial and tangential direction has been studied in air at 650 °C at two frequencies, 1 Hz and 0.1 Hz at a stress ratio of 0.1. The alloy shows a strong frequency and directionality effect. In both the directions, the forged turbine disc of IN 718 superalloy exhibits higher crack growth rate at 0.1 Hz as compared to that at 1 Hz. This was attributed to oxidation induced creep fracture under the selected test conditions. Further, higher crack growth rate has been observed in radial direction than tangential direction.