Elucidating the role of nickel in the corrosion behavior of laser-powder bed fused Monel 400 via potentiodynamic electrochemical impedance spectroscopy

In this study, Monel 400 was successfully fabricated using the laser powder bed fusion (L-PBF) process and systematically compared with pure nickel and wrought Monel 400 in terms of microstructure, texture, and electrochemical behavior to elucidate the influence of Ni content on the passivity and corrosion performance of L-PBF Monel 400 in 3.5 wt.% NaCl solution. The L-PBF Monel 400 exhibited a heterogeneous microstructure, in contrast to the uniform microstructures observed in pure Ni and wrought Monel 400. Furthermore, close-packed crystallographic planes dominated the textures of pure Ni and wrought Monel 400, whereas the L-PBF alloy showed a predominant {220} orientation. Potentiodynamic polarization and potentiodynamic electrochemical impedance spectroscopy results demonstrated that pure Ni possessed the highest corrosion resistance, followed by L-PBF Monel 400 and then wrought Monel 400. These findings indicate that Ni content plays a critical role in enhancing the corrosion resistance of Monel 400, while microstructure and texture are not the primary factors governing its electrochemical response. Potentiostatic polarization combined with X-ray photoelectron spectroscopy further substantiated these conclusions, revealing that higher Ni content promotes the formation of a more compact and protective passive film on the alloy surface.