Low-cycle fatigue behavior and creep-fatigue life prediction of three superalloys

The low-cycle fatigue tests with and without hold times were conducted in laboratory air at 816 degreesC and 927 degreesC under a total axial strain range control mode to investigate high-temperature fatigue and creep-fatigue interaction behavior of three superalloys, including HAYNES (R) 188, 230, and HASTELLOY (R) X. The fatigue life of three alloys at various total strain ranges and temperatures were compared. It was found that under both low-cycle fatigue and creep-fatigue loading conditions, the strain fatigue life of three superalloys were dependent on the type of the alloy, imposed total strain range, and test temperature. The different strain fatigue life behavior exhibited by three superalloys seemed to be related to the difference in the damages from creep and oxidation. The scanning electron microscopy examination on the fracture surfaces of the tested specimens revealed that both transgranular and intergranular crack propagation modes could be observed. In addition, the frequency-modified tensile hysteresis energy modeling was used to correlate the present strain fatigue life data. The result showed that this modeling could give a satisfactory prediction on the creep-fatigue life of three superalloys.