The fatigue behavior of a conventional, polycrystalline Inconel 718 alloy is compared to that of an experimental, single crystal aloy of equivalent nominal chemical composition. Differences between the fracture mechanisms exhibited by the two materials under cyclic loading were determined by scanning electron microscopy. The results of the fractographic analyses are presented on fracture mechanism maps that show the dependence of the fatigue fracture mechanisms on the maximum stress intensity factor, K_(max), and the stress intensity factor range, triangle openK. The relative effects of triangle openK and K_(max) on the fatigue crack growth behavior of these two allows are discussed within the context of a two-parameter crack growth law. The influence of grain boundaries on the fatigue crack growth resistance of materials such as Inconel 718 is also discussed in light of the results of this investigation.
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