Low cycle fatigue crack detection using A.C. potential drop method for CoCrAlY coated 738LC Ni base superalloy
Takaki Keisuke; Sakane Masao; Ohnami Masateru; Okabe Nagatoshi; Fujiyama Kazunari
Abstract:This paper studies the low cycle fatigue crack detection using the A. C. potential drop (ACPD) method for CoCrAlY coated 738LC Ni base superalloy. Push-pull low cycle fatigue tests were carried out at 1123 K in air using solid specimens with fast-fast and slow-fast waves. The low cycle fatigue life of the coated specimen was somewhat smaller than that of the uncoated specimen, but there exists no large difference between the two lives. In the fast-fast wave of the coated specimen, cracks were initiated at the specimen surface and propagated inside. In the slow fast wave test, some cracks were initiated at the interface between the coating and base metal in addition to the crack initiation at the specimen surface. ACPD method was able to detect the cracks initiated at the specimen surface and the interface. Especially low frequency ACPD is more sensitive than high frequency ACPD. The result of the electromagnetic FEM analysis agreed well with the experimental ACPD measurements. Key Words:superalloy, coating, creep-fatigue, low cycle fatigue, high temperature, crack propagation, A.C. potential drop(ACDP), electromagnetic field, finite element method(FEM)