Microstructure and Mechanical Performance of Inconel 617 Thin Wall fabricated via Wire Arc Additive Manufacturing

This study presents a comprehensive investigation into the microstructural evolution and mechanical performance of an Inconel 617 wall fabricated using the Wire Arc Additive Manufacturing (WAAM) process. Detailed microstructural characterization reveals a gradient in grain morphology along the build direction, driven by variations in thermal history. Equiaxed dendrites and columnar grains due to rapid solidification were noticed near the substrate and are mixed together in the bottom layers, while cellular structures and columnar dendrites are dominant in the middle layers. Elongated columnar dendrites are observed in the upper layers. In addition, Ti(C,N) secondary phases and precipitates such as M ₆ C and M ₂₃ C ₆ carbides are noticed within the austenitic matrix, are confirmed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The presence of these phases is further confirmed by X-ray diffraction (XRD), which finds their distinctive diffraction peaks. From hardness mapping, the build's average microhardness ranges from 237 HV at the bottom to 211 HV at the top, nearly matching the wrought Inconel 617's characteristics as outlined in ASTM B168-19. Anisotropy is clearly seen from the tensile tests, since the deposition direction achieves a higher average ultimate tensile strength (UTS) of 792 MPa than the build direction, which is 610 MPa. In all orientations, ductile fracture characteristics with dimples and voids are confirmed, suggesting significant plastic deformation before failure. The results demonstrate the importance of building orientation on material performance and validate the feasibility of the WAAM method for fabricating Inconel 617 components free of defects with desirable mechanical and microstructural integrity.