Effect of coherency and morphology of γ’ precipitates on fatigue crack growth in a single crystal Ni-base superalloy

Abstract

In order to investigate the effect of coherency and morphology of γ’ precipitates on fatigue crack growth in a single crystal Ni-base superalloy, fatigue crack propagation (FCP) tests were carried out at room temperature and 450°C using rafted specimens which had incoherent plate-like γ’ precipitates. The rafted specimens were extracted from a predeformed specimen which had been subjected to creep loading and then had fully rafted microstructure. The FCP behavior using rafted specimens was compared with the behavior in virgin state specimens which had cuboidal precipitates with coherency. A series of the experiments revealed that the FCP behavior and FCP rate are depending on the coherency and morphology of γ’ precipitates, which affects the plastic deformation around the crack tip and resultant preferential crack path.