Multiaxial Low Cycle Fatigue Life Evaluation of Nickel Base Single Crystal Superalloy Cruciform Specimen

Abstract

This paper describes the multiaxial low cycle fatigue life of cruciform specimen of YH61 Ni base single crystal superalloy at high temperature. Biaxial tension-compression low cycle fatigue tests were performed using the cruciform specimen at 1173K under y-directional strain amplitude (ε_y) constant condition with varying x-directional strain amplitude (ε_x). Low cycle fatigue lives were influenced by the strain biaxiality and the maximum lives were obtained at ε_x/ε_y being equal to 0.5. The maximum principal strain and Mises equivalent strain ranges gave a large scatter in the correlation of the multiaxial low cycle fatigue lives. The principal stress and Mises equivalent stress ranges showed far better correlation than the strain ranges. Cracking mode was also discussed by observing the fracture surface at failure. Cracks propagated in the 45 degree direction to x direction at ε_x/ε_y = -1 test while those in the x direction in the other cases. Cracks were initiated at the life ratio less than 0.2 at Ni₃(Al+Ta) eutectic alloy part and propagated with cycles.