Low cycle fatigue properties and microstructure evolution at 760 °C of a single crystal superalloy

Low cycle fatigue (LCF) behavior of a single crystal superalloy was investigated at 760 degrees C. Microstructure evolution and fracture mechanism were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results show that the fatigue data fluctuation was small and the fatigue parameters of the alloy had been determined. On increasing the cyclic number, the alloy initially showed slight cyclic softening at the early two or three cycles and slowly hardened to some extent afterwards, then kept stable for the most of the remaining fatigue life. The LCF of the alloy at 760 degrees C can be attributed to the main elastic damage in fatigue processing. The initiation site of fatigue crack was at or near the surface of the samples. Crack propagated perpendicularly to the loading direction at first and then along {111} octahedral slip planes. The fatigue fracture mechanism was quasi-cleavage fracture. The gamma' phase morphology still maintained cubic shape after fracture. There were a number of slip bands shear the gamma' precipitates and gamma matrix near the fracture surface of the specimen. The inhomogeneous deformation microstructure was developed by dislocation motion of cross-slip and a limited gamma' precipitate shearing by slip band, stacking faults or single dislocation was observed. (C) 2015 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.