Preparation and Properties of Ni60A-Cr₂O₃ Composite Coating on Surface of Automobile Piston Ring

The Ni60A-Cr₂O₃ composite coatings were prepared on surface of 45 steel for automobile piston ring by hypersonic plasma spraying. The effects of Cr₂O₃ content on the phase composition, microstructure, wear resistance and corrosion resistance of the Ni60A-Cr₂O₃ composite coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), frication and wear testing, electrochemical testing and immersion corrosion testing. The results show that in addition to the enhanced phase Cr₂O₃, FeNi₃, Fe(C, B)₆, Cr₂₃C₆ and other Cr precipitates were formed in the Ni60A-Cr₂O₃ composite coatings. With the increase of Cr₂O₃ content in the composite coatings, the wear-loss of the composite coatings decreased first and then increased, and the minimum value of the wear-loss was obtained when the Cr₂O₃ mass fraction was 35%, and the suitable amount of Cr₂O₃ added to the Ni60A-Cr₂O₃ composite coatings was 35%. The wear mechanism of the Ni60A coating and the 35% Cr₂O₃ + 65% Ni60A composite coating were adhesive wear and abrasive wear, respectively. The test results of polarization curves and immersion corrosion test showed that the corrosion resistance of 35% Cr₂O₃ + 65% Ni60A composite was better than that of the Ni60A coating both in 1.5 mol/L H₂SO₄ solution and in 3.5% NaCl solution.