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Fatigue Crack Initiation and Mechanism of GH4133B Superalloy Used in Turbine Disk of Aero-Engine

The fatigue crack initiation life at various stress ratios for GH4133B superalloy specimen with different circular notch radios are studied at ambient temperature and atmospheric pressure utilizing the fracture mechanics method. It is shown that a controlling parameter ΔKI/ρ0.5 can be adopted to characterize the fatigue crack initiation life, and the effect of notch radius on fatigue crack initiation life increases with increasing control parameter, while the fatigue crack initiation life firstly increases and then decreases with increasing stress ratio. The fatigue fracture surfaces of circular notched compact tension specimens of GH4133B superalloy for fatigue crack initiation tests at various stress ratios are investigated using a scanning electron microscopy, and the fracture surface morphologies in the fatigue source region are analyzed. It is found that the separation between carbide inclusion on the surface or subsurface and matrix, or the separation between nickel-rich second phase particle and matrix, or the interaction between persistent slip bands and inclusion, mainly results in the fatigue crack initiation.