Synergistic effect of transpassive film and gamma double prime phase on the electrochemical dissolution behavior of Inconel 718 manufactured by laser directed energy deposition

This study investigated the synergistic effect of transpassive film and γ″ phase on the electrochemical dissolution behavior of Inconel 718 manufactured by laser directed energy deposition. The investigation was based on samples after homogenization and aging with (γ + γ″) phases and homogenization with γ phase. The compositions of the transpassive films for two kinds of heat-treated samples were similar, mainly comprising porous Ni hydroxides. The incompact transpassive film induced the local preferential dissolution of the γ matrix and generated multiple dispersive pits on the surface. Compared with the sample after homogenization, the spatial distribution of the γ″ phase in the sample after homogenization and aging restricted the expansion of pits in the γ matrix, leading to superior surface quality. The detachment of the γ″ phase during electrochemical dissolution provided extra mass loss and higher current efficiency. A qualitative model was proposed to demonstrate the synergistic effect of the transpassive film and γ″ phase on the dynamic electrochemical dissolution process.