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

Fatigue crack propagation fracture surface morphologies in nickel-base superalloys vary substantially with changes in loading parameters such as temperature, ΔK, 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 ΔK, 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.