Defects-Induced Fatigue Failure Behavior and Life Prediction of Laser Powder Bed Fusion GH4169 Superalloy in High and Very-High Cycle Regimes

Laser powder bed fusion (LPBF) is a leading method for fabricating high-strength materials such as GH4169 superalloy. However, their deformation behavior must be thoroughly analyzed before they can be used in critical engineering applications. The fatigue behavior of LPBF GH4169, particularly in the very-high cycle regime, is not yet fully understood. Therefore, uniaxial fatigue tests are conducted to investigate high and very-high cycle fracture analysis and associated failure behaviors in the solution-aged condition under two stress ratios at room temperature. Subsequently, scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy are employed to observe the dislocation structures and fracture mechanism. Fracture surfaces reveal that cracks nucleate through a single site, typically on the surface or within the interior, driven by manufacturing or crystallographic defects. Interior failure is evident at lower stress amplitudes, with two distinct crack nucleation modes identified. Dislocation accumulation and interactions with δ phases are revealed. Furthermore, the coupling reinforcement of strengthening phases enhances the fatigue performance. Moreover, the threshold values as well as the transition sizes from small to long cracks increase as failures shift from surface to interior. Finally, a fatigue life prediction model is developed, demonstrating a strong correlation to the experimental results.