Microstructure, Mechanical Properties and Corrosion Behavior of Inconel 617 Superalloy Fabricated by Wire Arc Additive Manufacturing

In this work, the microstructural features, mechanical properties, and localized corrosion performance of a single-layered wall of nickel-based superalloy Inconel 617 produced via wire arc additive manufacturing (WAAM) were examined. Microstructural analysis revealed the existence of cellular and equiaxed dendrites in the bottom layers, while elongated columnar dendrites having a size up to 2 mm were observed in the middle and top layers due to different cooling rates and temperature gradients. Electron micrographs and energy-dispersive x-ray spectroscopy analysis confirmed the segregation of precipitates in the interdendritic regions of the austenitic matrix. Carbides such as Ti (C, N) and Cr23C6 existed in the interdendritic regions and are caused by the diffusion of Cr, Mo, and C elements during the WAAM process. Assessment of the mechanical properties revealed the excellent hardness (244-286 HV) and tensile properties of WAAM-printed IN617. The average yield strength, tensile strength, and elongation of IN617 specimens were 400 MPa, 724 MPa, and 43%, which is comparable with the ASTM B168-19 standard grade. The fracture surface analysis highlighted the ductile mode of fracture with dimples and micro-voids. Potentiodynamic polarization results illustrated the absence of significant anisotropic nature of the pitting resistance in 3.5% NaCl solution. The corrosion rate of the WAAM-printed IN617 specimens ranged between 1.02 and 1.07 mpy in 3.5% NaCl solution and the size of the pit was having a size of 30 to 100 mu m. Electrochemical measurements indicate that the excellent pitting behavior is attributed to the formation of stable passive films along with higher corrosion potential and lower current density values. This study shows that the WAAM process can be potentially applied to other alloys for fabricating structures to obtain critical information on the corrosion damage.