Effect of post-heat treatment on corrosion resistance and microstructural characteristics of CMT-WAAM Inconel 718 in 3.5 % NaCl solution

Abstract

This study investigates the electrochemical corrosion performance and microstructural evolution of Inconel 718 (IN718) produced via Cold Metal Transfer-based Wire Arc Additive Manufacturing (CMT-WAAM). The corrosion performance of as-deposited and API Heat-Treated (HT) samples was evaluated in a 3.5 % NaCl solution using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and Scanning Electron Microscopy (SEM). The API heat treatment involved solution treatment and homogenization at 1080 °C, followed by double aging at 720 °C and 620 °C. Heat-treated samples exhibited reduced corrosion current density (i_corr) and increased polarization resistance (Rp), alongside a more positive corrosion potential (E_corr) compared to as-deposited samples. EIS measurements confirmed enhanced passivation with lower passivation current density, while microstructural characterization revealed reduced Laves phase intensity, refined grains, and improved elemental distribution in heat-treated samples. AFM confirmed that heat-treated specimens exhibited a smoother surface morphology, while SEM revealed fewer surface cracks and enhanced passivation. These findings underscore the importance of API heat treatment in enhancing the corrosion resistance of WAAM-processed IN718.