On the corrosion of additively manufactured Inconel 718 with different crystallographic orientations exposed to 3.5% NaCl

This study investigated the corrosion properties and behavior of laser powder bed fusion fabricated (LPBFed) IN718 with various crystallographic orientations using potentiodynamic polarization curves, electrochemical impedance spectroscopy, and electrochemical etching. Interestingly, the sample with the strongest texture did not exhibit the lowest corrosion rate in 3.5% NaCl solution; instead, the sample with a mixed orientation demonstrated the highest corrosion resistance. The corrosion resistance in a 3.5% NaCl solution increases in the order of mixed-ND (Normal Direction) (110)/ (111)> strong-ND (100)> weak-ND (100)> strong-ND (110)> strong-ND (120). A combination of multiscale characterization revealed that the critical factor influencing corrosion resistance is the proportion of cellular walls to the interiors rather than crystallographic orientation. This is attributed to the uneven distribution of elements within the cellular walls and interior, leading to a micro-galvanic coupling effect that drives corrosion behavior. The underlying reason is that a higher proportion of cellular walls, consisting of Laves phases and solute segregations, can enhance the stability of the passivation film. Increasing the proportion of cellular walls by adjusting laser parameters, even in a randomly orientated IN718, the as-built IN718 can attain a better corrosion resistance than the hot-rolled and as-cast IN718. The findings in this work offer insights into principles and methodology for enhancing the corrosion resistance of IN718 alloys in additive manufacturing.