New insights of the microcrack initiation induced by Mo addition in Ni-based single crystal superalloys during creep at 900 °C

Mo has received much attention in Ni-based single crystal superalloys as a main strengthening element at elevated temperatures above 1000 °C. However, the effects of Mo addition in new generation single crystal superalloys at medium temperature conditions are still not clear. This paper investigated the creep property at 900 °C and 392 MPa in a 4th generation Ni-based single crystal superalloy with different Mo contents, indicating that Mo addition decreased the creep life and induced large amounts of microcracks. Higher Mo content could weaken the interface strength by inducing more stacking faults, causing crack initiation along the interface. The elemental segregation along the stacking faults triggered the nucleation of other precipitates, which could further lead to cracks. The precipitation of topologically close-packed (TCP) phases introduced by more Mo addition caused crack initiation along the interfaces between the TCP phases and γ′ phase. By investigating the microcrack formation induced by Mo during creep at 900 °C, we provided a new perspective for the alloy design.