Effects of Hold Time on the Elevated Temperature Fatigue Crack Growth Behavior of Alloy 247LC‐DS

ABSTRACT Creep–fatigue crack growth (CFCG) experiments were performed at 850°C and 950°C on nominally 12.70‐mm‐thick compact‐type specimens of alloy 247LC‐DS, a Ni‐base superalloy. The loading cycles consisted of trapezoidal waveforms with hold times of 2 and 20 min at the maximum force. The crack plane was oriented normally to the solidification direction. The fracture surfaces and the crack path‐microstructure interactions were characterized. Competing time‐ and cycle‐dependent mechanisms contributed to crack growth during these tests. Time‐dependent crack growth rates, , at 850°C and 950°C correlated with for 2‐min and 20‐min hold durations. These CFCG rates were also comparable to the creep crack growth (CCG) rates previously reported. Crack growth rates showed significant variability under all test conditions. This scatter was attributed to the formation of microcracks connecting into secondary cracks in the interdendritic regions aligned with the solidification direction. Material models representing the CCG and CFCG data are described.