Problems with corrosion resistance in hydraulic cylinders used in marine environments contribute to many failures. Thermal spraying has proven to be a reliable method for replacing electroplated coatings in aircraft, but performance in high corrosive environments is still a drawback. In the present work, a new sealing method to densify WC-CoCr HVOF coatings is tested, which appears to be applicable to hydraulic cylinders in marine environments. The method is based on the use of nanoparticle solutions that penetrate and fill pores and cracks to seal the coatings. Two such solutions are tested and compared to as-sprayed coatings. Open-circuit potential and tribocorrosion measurements in 3.4% NaCl show that sealed coatings are more resistant to corrosion and wear than as-sprayed layers.