Corrosion Behavior of Ni-Based Coatings Reinforced with Chromium Carbide Particles Deposited by Plasma Transferred Arc in a Hydrochloric Acid Solution

The Ni-based coatings with different chromium carbide contents were deposited on H4140 steel by a plasma transferred arc process. The corrosion behavior of Ni-based chromium carbide coatings in a 0.5 mol/l HCl solution was studied by means of the potentiodynamic polarization curve, electrochemical impedance, and immersion corrosion test. The coatings were metallurgically bonded with the substrate. The addition of Cr₃C₂ particles resulted in more Cr-rich carbides in the coatings. In a 0.5 mol/l HCl solution, the four as-received coatings show active anodic dissolution due to the joint action of hydrogen and chlorine ions. With an increase in the Cr₃C₂ content, the corrosion potential of coatings shifts in the positive direction, the corrosion current density decreases, and the corrosive resistance of the coating is enhanced. The galvanic corrosion occurred between the Cr-rich carbides and the γ-Ni matrix phase, the coatings reinforced with chromium carbide particles showed preferential selective corrosion of the γ-Ni matrix phase. The cracks and pits are migration channels of the corrosion medium into the coating, causing a more serious corrosion damage.