Fatigue and short crack propagation behaviour of cast nickel base alloys in 713 C and MAR-M-247 LC at high temperatures

Cast nickel base alloys are used for integral turbine wheels of turbochargers and small gas turbine engines. Fatigue tests on unnotched specimens under constant strain amplitude loading were carried out in the temperature range of 400 degree C to 760 degree C without and with hold times in order to determine the monotonic and cyclic stress-strain and failure behaviour including crack initiation and propagation of short cracks starting from natural material defects. Additional CT- specimen tests showed that the crack propagation rate of short cracks is much higher than that of long cracks.