Simultaneous creep–fatigue damage accumulation of forged turbine disc of IN 718 superalloy

In the present study, simultaneous creep–fatigue interaction of rim, hub and bore section of forged turbine disc of IN 718 superalloy as per the Kartik–Vikas test method has been presented. Metallographic assessment of interrupted test specimens confirmed the ‘true interaction’ mode of simultaneous creep–fatigue interaction where transgranular initiated crack gets perturbed by accumulating creep damage and becomes intergranular. The cause of intergranular cracking can be attributed to the combined effect of planar slip and oxidation. The superalloy showed significant reduction in fatigue life under simultaneous creep–fatigue interaction as compared to pure fatigue loading conditions. This was attributed to high activity of dislocations and grain boundary damage in creep–fatigue interaction as compared to pure fatigue loading conditions.