Study on the anisotropic high cycle fatigue performance of L-DEDed Ni-based superalloy: Microstructure, failure mechanism and fatigue limit evaluation

Ni-based superalloys are usually utilized in hot-section components of gas-turbines and aeroengines, which are prone to fatigue failure under the rotational and vibrant working condition. The anisotropic mechanical properties of laser additive manufactured (LAMed) Ni-based superalloy is evident due to its unique microstructure of directional grown dendrites in columnar grains. This study assessed the anisotropic high cycle fatigue behavior of LAMed GH4169 Ni-based superalloy at ambient temperature. In this respect, vertical and horizontal specimens were tested, and the influence of microstructure on the anisotropy in fatigue resistance were studied. Results show that the vertical fatigue specimen has a higher fatigue resistance than the horizontal counterpart, which is mainly influenced by the combined effect of secondary phases and grain morphology during the short fatigue crack propagation period. A microstructure with less <001> -textured grains containing secondary phases parallel to the loading direction of vertical specimens shows lower short fatigue propagation rate than the horizontal specimen. Besides, higher tensile strength with less tensile residual stress, accompanied with longer fatigue crack propagation length during the long fatigue propagation period also minorly contributes to the higher fatigue resistance of the vertical specimen. Meanwhile, the fatigue limit was compared in the form of fatigue limit ratio of the vertical to horizontal specimen with the Murakami model, using the primary dendrite arm spacing lambda 1 as the Murakami parameter factor considering the effect of tensile residual stress has a closer predicted fatigue limit ratio to the experimental value.