Sealing HVOF Thermally Sprayed WC-CoCr Coatings by Sol-Gel Methods

The offshore industry faces challenges with corrosion resistance in hydraulic cylinders used in marine environments. Thermal spray coating appears to be a promising technique for replacing electroplated coating in many applications, but the performance of thermal spray coatings in highly corrosive environments must be improved. In the present work, a new sealing method for HVOF WC-CoCr coatings for their application on hydraulic cylinders for marine environments has been tested. The method consists of applying sol-gel solution that can penetrate, fill, and thus seal the pores and cracks in the coating. The sealed coatings have been tested with and without posttreatment and compared with as-sprayed coatings. Open-circuit potential (OCP) and tribocorrosion tests in 3.4% NaCl were performed to evaluate the performance of the sealing method. Both tests showed that the sealed coatings had the best performance.