Effects of deformation behavior on fatigue fracture surface morphology in a nickel-base superalloy

Abstract Fatigue crack propagation fracture surface morphologies in nickel-base superalloys vary substantially with changes in loading parameters such as temperature, Δ K , load ratio, frequency, and additionally microstructure. Quantitative fracture surface roughness can vary from sub-micron levels to a maximum value of approximately half the grain size. Atomic Force Microscope studies of surface slip traces in compression specimens revealed a clear relationship between slip homogeneity in compression testing and fracture surface roughness under similar fatigue loading conditions. It has been shown in this study that changes in Δ K , strain level, temperature, grain size, and load ratio can all affect slip heterogeneity, which in turn controls the fracture surface roughness. Finally, a model is developed that quantitatively predicts fracture surface roughness and roughness-induced crack closure stress intensity values from measurements of slip line spacing in a compression specimen.