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

The fatigue crack growth behavior of an experimental, single crystal alloy, of equivalent nominal chemical composition to Inconel 718 is presented. Fr acture modes under cyclic loading were determined by scanning electron micr oscopy. The results of the fractographic analyses are presented on a fractu re mechanism map that shows the dependence of the fatigue fracture mechanis ms on the maximum stress intensity factor, K-max, and the stress intensity factor range, Delta K. Crack-tip deformation mechanisms associated with fat igue crack growth were studied using transmission electron microscopy. The relative effects of Delta K and K-max on the fatigue crack growth behavior of this material are discussed within the context of a two-parameter crack growth law. The influence of rain boundaries on the fatigue crack growth re sistance of materials such as Inconel 718 is also discussed in light of the results of this investigation. (C) 1999 Acta Metallurgica Inc. Published b y Elsevier Science Ltd Ali rights reserved.