The high temperature low cycle fatigue behavior of cast nickel based superalloy K417

Fully reversed total strain-controlled low cycle fatigue tests were conducted on cast nickel based superalloy K417 at 650 degreesC and 900 degreesC in air. It was found that a substantial reduction in fatigue life occurred as the testing temperature was increased from 650 degreesC to 900 degreesC under lower total strain amplitudes. The cyclic stress response of the alloy is mainly related to the total strain amplitude and testing temperature. Optical and scanning electron microscopes (SEM) revealed that during testing at 900 degreesC gamma' precipitates coarsened and a rafting microstructure developed. The SEM analysis of fracture surfaces shows that the fatigue crack initiation was frequently associated with porosities. At temperatures of 650 degreesC and 900 degreesC the fatigue crack initiation and propagation are both transgranular for all the total strain amplitudes under consideration.