Low-cycle fatigue behavior of DZ125 superalloy under prior exposure conditions

Low-cycle fatigue (LCF) behavior of the directionally solidified (DS) nickel-based DZ125 superalloy was studied at elevated temperature (980 °C). Specimens were, respectively, exposed for 0, 2, 25, 50, and 100 h in air. The fatigue life of pre-exposed specimens is lower than that of unexposed specimens. The result is closely associated with fatigue crack initiation and propagation due to oxygen embrittlement and cycle loading. Detailed fractographic evaluations indicate the fatigue life is closely related to the surface microstructural modification. The resulting changes in microstructure cause the decrease in the effective area and the increase in actual stress. A methodology based on the continuum damage mechanics is developed to describe the correlation between the residual LCF life and pre-exposed time.