Fatigue growth of surface cracks in nickel-based superalloys

Abstract The fatigue growth of surface cracks in three nickel-base superalloys has been monitored using a DC electrical potential-drop technique at both 200°C and 600°C in air. A three dimensional finite element analysis stress intensity calibration has enabled these growth rates to be compared with standard data obtained from though-cracked compact tension specimens. Good agreement has been found between surface and through-crack growth rates over the range from threshold to ∼25 MNm −3 2 although for applied stress intensity ranges in excess of this the surface cracks propagated more slowly than expected, particularly at 200°C. This retardation has been suggested to arise from the increased proportion of a plane stress crack growth for the shorter surface cracks leading to both increased closure effects and a change in the crack growth mechanism.