Influence of Cr on Corrosion Resistance of HVAF WC-Co Coats to Neutral Salt Spray

Corrosion resistance of high-velocity-airfuel(HVAF) WC-Co and WC-CoCr coats was investigated in this paper.The coats were characterized by XPS and electrochemical analysis.XPS analysis showed that the chemical states of adhesive phase in HVAF WC-Co coat was simple substance Co and in WC-CoCr coat were Co and Cr₂O₃.Electrochemical polarization showed that the corrosion potential of steel substrate was improved after HVAF WC-Co treatment;while the potential was further improved when adding Cr into WC-Co.Neutral salt spray for 400h displayed that WC-CoCr coat exhibits better corrosion resistance than WC-Co coat.The SEM observation revealed that the adhesive phase is preferentially corroded due to micro-electrochemical corrosion and when the corrosion mediun comes to interface,corrosion of the substrate occurs.For HVAF WC coat,the corrosion were governed by corrosion of adhesive phase,pervasion of corrosion medium and final corrosion of interface between HVAF WC coatings and substrate.Cr exists as Cr₂O₃ passive phase,which is beneficial to the corrosion resistance of HVAF WC-Co coat.