Study Of Corrosion-resistance Of Plasma Sprayed Cr₂O₃-8TiO₂ Ceramic Coatings

In this paper, Cr₂O₃-8TiO₂ ceramic coatings (with and without bonding coating of NiCrAI) were prepared by Plasma Spraying (PS). Cr₂O₃-8TiO₂ ceramic coatings and hard chrome plating coatings' properties and their corrosion behaviours in different corrosion conditions were studied.The microstructures of ceramic coatings and hard chrome plating were observed by using Optical Microscopy (OM) and Scan Electron Microscope (SEM). X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS) were used to measure the components of the coatings. The microhardness, porosity and the bonding strength of Cr₂O₃-8TiO₂ coatings were tested.The plasma sprayed Cr₂O₃-8TiO₂ coating has a typical laminar structure with about 4 % porosity. The reasons for the porosity forming were discussed in this paper, and Cr₂O₃-8TiO₂ coating was dipped in epoxy resin in order to seal up pores or micro-cracks. A relatively high micro-hardness with large variation between 727²518Hv was observed for Cr₂O₃-8TiO₂ coating, nearly twice as hard as hard chrome plating with micro-hardness of 856Hv.The corrosion behaviours of Cr₂O₃-8TiO₂ coatings were studied and were compared with the hard chrome plating in salt mist, 10% (mass) NaOH, water (35℃, 65℃, 95℃) and 10%(mass) HCl. And an electrochemical system was used to measure the Tafel polarization curves of Cr₂O₃-8TiO₂ coating, hard chrome plating, and C45 steel in order to better understand the corrosion resistances of Cr₂O₃-8TiO₂ coatings and hard chrome plating. The results show that Cr₂O₃-8TiO₂ coating has a better corrosion resistance.In addition, Cr₂O₃-8TiO₂ coatings and hard chrome plating displayed different corrosion tendencies in different corrosion medium: 10%(mass) NaOH2O₃-8TiO₂ coating was uniform corrosion, which took place on the coating surface;the corrosion caused the decrease of the Cr₂O₃-8TiO₂ coating density.The temperature influenced coatings' corrosion resistances. An equation between coating cumulative weight loss and corrosion time, temperature for Cr2O3-8TiO2 coating was obtained in this paper: V =1.54x KT'W106Ar xt, V is the cumulative weight loss (g/m2);T is medium temperature (K);t is corrosion time (h).In conclusion, all the analysis indicated that the plasma sprayed Cr2C>3-8TiO2 ceramic coating has a better corrosion resistance than hard chrome plating.