Creep-Fatigue Crack Initiation and Incipient Growth Behavior for Ni-Base Single Crystal Superalloy

Abstract

The fatigue and creep-fatigue crack initiation and growth behaviors of Ni-base single crystal superalloy TMS 12 were investigated at room temperature and 920°C using double edge notched specimens. At room temperature the fatigue incipient crack growth from the notch occurred by failure on the (111) plane, and the crack growth was not dependent on the number of cycles. At 920°C the crack growth behavior did not exhibit anisotropic fracture, which is caused from multiple slips. Under creep-fatigue and creep, rhombic cavities were observed at the crack tip vicinity. Alpha wolfram precipitates were observed at the sites of cavities. Cracks initiated from the interface rafted γ' and γ at alpha wolfram precipitates in (100) plane, which formed square-type cavities.