Micromechanisms of fatigue crack growth in a forged Inconel 718 nickel-based superalloy

The micromechanisms of fatigue crack propagation in a forged, polycrystalli ne IN 718 nickel-based superalloy are evaluated. Fracture modes under cycli c loading were established by scanning electron microscopy analysis. The re sults of the fractographic analysis are presented on a fracture mechanism m ap that shows the dependence of fracture modes on the maximum stress intens ity factor. K-max, and the stress intensity factor range, Delta K. Plastic deformation associated with fatigue crack growth was studied using transmis sion electron microscopy. The effects of Delta K and K-max on the mechanism s of fatigue crack growth in this alloy are discussed within the context of a two-parameter crack growth law. Possible extensions to the Paris law are also proposed for crack growth in the near-threshold and high Delta K regi mes. (C) 1999 Elsevier Science S.A. All rights reserved.