Long-term Corrosion Behavior of WC-based Cermet Coatings by HVOF Spraying

WC-Ni and WC-Cr₃C₂-Ni coatings were prepared on Q235 steel substrate by HVOF spraying technology.X-ray diffractometer and metallurgical microscope were used to analyze the phase composition and structure of the coatings.The corrosion resistance of the coatings in 3.5wt% NaCl solution was studied by electrochemical workstation and full immersion experiment. The results show that the two coatings have uniform and dense structures, and the porosities of the WC-Ni and WC-Cr₃C₂-Ni coatings were respectively 1.71% and 1.15%. In the 3.5wt% NaCl solution, both coatings produce passivation, and the passivation film on the coating surface improve the corrosion resistance. During the long-term immersion corrosion process in 3.5wt% NaCl solution, the wear mass loss of the WC-Cr₃C₂-Ni coating is less than that of WC-Ni coating,implying that the corrosion resistance of the WC-Cr₃C₂-Ni coating is better than that of the WC-Ni coating. After being immersed for 28 d, the surface structure of the WC-Ni coating is relatively loose with small and densely distributed pores,while the surface of the WC-Cr₃C₂-Ni coating is relatively flat with large and sparsely distributed pores. The loose structure and high porosity cause corrosive ions to penetrate into the pores and grain boundaries of the coatings, then,the corrosion resistance of the coatings reduces.