Interaction of fatigue and creep in MAR-M 247 superalloy

Abstract

Lifetime of MAR-M 247 Ni-based superalloy was experimentally studied under high-frequency cyclic loading (120 Hz) with constant tensile mean stress m = 300 MPa at temperature 900 °C in air. The stress amplitude a was changed in order to investigate the superalloy lifetime in a wide range of conditions, from pure creep to pure fatigue. The superposition of the stress amplitude on the mean stress does not influence the specimen lifetime until a threshold value is reached. Scanning electron microscopy was utilized for the fracture surface observation with the aim to identify the governing damage mechanisms for particular test conditions.