On Fabrication of Inconel 718 Slab by Wire Arc Additive Manufacturing: Study of Built Microstructure and Mechanical Properties

A slab of dimension (152 x 25 x 18) mm(3) is successfully fabricated through Cold Metal Transfer + Metal Inert Gas-based Wire Arc Additive Manufacturing (WAAM). 4.3 kg/h deposition rate is achieved. WAAMed Inconel 718 exhibits dendritic microstructure which grows along the build direction. In the solid solution matrix of Ni-Cr-Fe, the Laves phase, Nb-rich MC-type carbides, and delta (d) phases are detected. The average tensile strength along the horizontal direction is obtained as similar to 824 MPa. Location-specific microstructure evolution causes a significant extent of property anisotropy predominantly along the build direction. The horizontal tensile specimen extracted from the bottom region of the slab exhibits the highest tensile strength (UTS), while the lowest tensile strength is obtained for the specimen extracted from the middle zone of the fabricated slab. Temperature data as recorded by the thermocouples are utilized to understand the complex heat interaction phenomena during the WAAM process. Laves phase is completely dissolved during homogenization treatment thus microstructure of the aged specimen only consists of the strengthening phase, i.e., gamma'' (Ni3Nb) and Nb-rich MC carbides.