Fundamental mechanisms of surface damage associated to the localization of the plastic deformation in fatigue

Nowadays fatigue damage is becoming a very important issue for it may lead to a service failure at any moment. In low cycle fatigue, the crack initiations influence strongly the fatigue life of a material. The study done here is carried out on Waspaloy™at its under-aged state, a superalloy based Nickel characterized by the hardening precipitates, γ′ in matrix Nickel, γ. Fatigue resistance depends on the material microstructure. Damage mechanisms due to the localization of plastic deformation by fatigue are studied on the precipitate and grain from nano to meso scale. This work aims to have a better understanding on the crack initiation mechanisms related to the metallurgical parameters: the influence of the grain and γ′ size. Complete investigation is performed by using multiple analysis instruments: SEM and AFM.