Fatigue crack initiation behaviors around defects induced by welding thermal cycle in superalloy IN617B

In this study, fatigue crack initiation behaviors around defects induced by welding thermal cycle in IN617B were investigated by in-situ fatigue tests combined with DIC (Digital Image Correlation) and EBSD (Electron Back Scattering Diffraction) characterization. Two mechanisms of fatigue crack initiation around defects were clarified and the distance of crack initiation position from defects was proposed to determine which mechanism was dominant. Intergranular fatigue crack initiation caused by pile-up of dislocations was dominant in the far-field region from defects, while intragranular fatigue crack initiation caused by cracking at the interface between dislocation bands and matrix was dominant in the near-field region from defects. Welding defects altered the fatigue crack initiation mechanism by changing the deformation mode of the near-field region, thereby accelerating the fatigue failure process of IN617B alloy.