Revealing the role of sealing treatment on the electrochemical corrosion properties of HVOF-sprayed WC–20Cr3C2–7Ni/MWCNTs coating

Abstract

In this study, the WC–20Cr3C2–7Ni/MWCNTs coating was prepared by high-velocity oxy-fuel (HVOF) spraying. Coatings were sealed with two types of sealants (i.e., silicone resin and aluminum phosphate) using both conventional and vacuum impregnations. Sealing treatments were investigated for their effect on coating microstructure and electrochemical corrosion behavior by scanning electron microscopy (SEM), contact angle measurement, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. According to the results, all four sealing methods enhanced the coating's corrosion resistance. The vacuum impregnation sealing process removed residual air from pores and microcracks, permeating these defects as much as possible with the sealants. In contrast to silicone resin sealants, aluminum phosphate sealants had the opposite effect on sealing since bound water evaporated during heat treatment, which contributed to the formation of defects in the path as a result of the thermal stress. Among all four sealing methods, sealing with silicone resin organic sealant under vacuum impregnation had the highest charge transfer resistance (Rct) and polarization resistance (Rp), the lowest free corrosion current density (Icorr), and the largest capacitive arc radius and impedance modulus, which significantly improved the coating's corrosion resistance.