An assessment of three creep-fatigue life prediction methods for nickel-based superalloy GH4049

High-temperature low-cycle fatigue tests with and without a 10-s strain hold period in a cycle were performed on a nickel base superalloy GH4049 under a fully reversed axial total strain control mode. Three creep-fatigue life prediction methods are chosen to analyse the experimental data. These methods are the linear damage summation method (LDS), the strain range partitioning method (SRP) and the strain energy partitioning method (SEP). Their ability to predict creep-fatigue lives of GH4049 at 700, 800 and 850 degrees C has been evaluated. It is found that the SEP method shows an advantage over the SRP method for all the tests under consideration. At 850 degrees C, the LDS and SEP methods give a more satisfactory prediction for creep-fatigue lives. At the temperatures of 700 and 800 degrees C, the SRP and SEP methods can correlate the life data better than the LDS method. In addition, the differences in predictive ability of these methods have also been analysed. The scanning electron microscopy (SEM) examination of fracture surfaces reveals that under creep-fatigue test conditions crack initiation mode is transgranular, while crack propagation mode is either intergranular plus transgranular or entirely intergranular, dependent on test temperature.