| Abstract Scope |
Selective laser melting (SLM) produces unique microstructures (e.g., epitaxial columnar grains, texture, etc.) that influence mechanical properties. In this work, the fatigue crack growth behavior of SLM produced Alloy 718 was examined at 25°C and 650˚C in an air environment for two cracking orientations relative to the build plane, and two post heat treatments: 1) solutionized and duplex aged and 2) hot isostatic pressed (HIP), solutionized, and duplex aged. HIPing was found to recrystallize much of the columnar microstructure and eliminate a weak anisotropy in 25°C fatigue crack growth rates seen for the non-HIPed structure; however, growth rates and thresholds remained well below that of wrought material. At 650˚C, anisotropy in fatigue crack growth rates became more significant when the crack growth mechanism shifted to stress assisted grain boundary oxidation (SAGBO). Microstructure analysis, fractography, and observations of crack profiles were used to understand the microstructure influence on fatigue crack growth. |