Fracture failure analysis of DZ125 directionally solidified superalloy under combined high and low cycle fatigue

Fracture failure behaviors of DZ125 directionally solidified nickel-base superalloy under combined high and low cycle fatigue (CCF) loads are investigated in this study. It is found that competitive cracking behaviors are present in DZ125 alloy while subjected to different CCF loads. An increase in the maximum low-cycle fatigue (LCF) nominal stress or high-cycle fatigue (HCF) stress amplitude results in a transition of crack initiation sites from subsurface pores or carbides to surface oxides. As the cycle ratio of HCF to LCF rises, crack initiation sites shift from subsurface carbides to surface oxides.