THE CYCLIC CREEP-BEHAVIOR OF NICKEL-BASE SUPERALLOY IN738LC

The cyclic creep response of the polycrystalline nickel base superallo y IN738LC at 950 degrees C was investigated. The effect of applied str ess and hold time at the reduced stress was studied and the behaviour was compared with that of static creep. Both the static and the cyclic creep tests showed a distinct softening behaviour with increasing str ain. As compared to cyclic creep without hold and static creep, the cy clic creep with hold time shows substantially higher strain rate, frac ture strain, fracture time and number of cycles to fracture. A signifi cant recovery of the dislocation structure during the hold time at the reduced stress level is responsible for the enhanced fracture life an d strain rate under these deformation conditions. The cyclic behaviour is rationalised on the basis of observed change in gamma' morphology and dislocation recovery during the hold period.