The Microstructure and Corrosion Resistance of Inconel 718 Coating by Plasma-Enhanced High-Velocity Arc Spraying

Abstract

The study aimed to investigate the effect of spraying distance on the microstructure and corrosion resistance of Inconel 718 coatings applied using the plasma-enhanced high-velocity arc spraying (PEHAS) technique, especially under the influence of hydrogen plasma gas. For this purpose, the coatings were produced at four different spraying distances: 100, 150, 180, and 200 mm, and the samples obtained were referred to as SA, SB, SC, and SD, respectively. In addition, the microstructure and phase composition of the coatings were investigated, as well as the corrosion behavior of the coatings when immersed for 0-168 h in a 3.5% wt.% NaCl solution. It was determined that the Inconel 718 coatings consisted mainly of Ni-Cr-Fe solid solutions with small amounts of oxides (NiO, Fe₂O₃, Cr₂O₃, Nb₂O₅). The oxide content within the coatings increased with greater spraying distances. Sample SC featured the lowest porosity (0.88 ± 0.08%) and the highest microhardness (505 ± 25 Hv_0.1). Electrochemical assessments, including polarization curves and electrochemical impedance spectroscopy (EIS), showed that samples SA, SB, and SC experienced an initial drop followed by a rise in corrosion potential and an initial increase followed by a decrease in corrosion current density during the immersion cycle. In contrast, the corrosion potential of sample SD consistently decreased. Over time, the formation and accumulation of corrosion products with inerts on the coatings surface helped seal the pores and prevent further corrosion. After a comprehensive analysis, it was concluded that sample SC had the most effective corrosion resistance after 168 h of immersion, evidenced by its elevated resistance to pore penetration (R_p), charge transfer (R_dl), and overall impedance modulus.