High-cycle fatigue behavior of an additively manufactured Inconel-type Ni-based superalloy at 900 °C

This paper investigates the high-cycle fatigue behavior of an additively manufactured Inconel-type Ni-based superalloy, GH3625, at 900 °C. Stress-life responses were measured for specimens with different build orientations, and the fatigue mechanisms were examined using transmission electron microscopy, electron backscatter diffraction, and fracture-surface analysis. The results show that the fatigue performance is orientation dependent. At 900 °C and a stress ratio of 0.1, the transverse specimens exhibit a higher fatigue limit than the longitudinal specimens. Under high stress levels, fatigue failure is associated with low dislocation density, limited dislocation interaction, and rapid crack propagation. Under lower stress levels, a higher dislocation density and more developed dislocation structures help suppress crack initiation and extend fatigue life. EBSD results further indicate that fatigue life is influenced by grain orientation distribution, grain size, and the fraction of low-strain grains. A higher fraction of fine, low-strain grains improves resistance to fatigue crack initiation. Fracture observations support these mechanisms, showing rougher fracture surfaces for high-stress specimens and flatter surfaces with slower crack growth for low-stress specimens. These findings clarify the microstructural factors that control the high-temperature high-cycle fatigue behavior of additively manufactured GH3625 superalloy.