Enhanced erosion-corrosion resistance of monolithic ENP coating on ductile cast iron by using electrochemical pretreatment and heat treatment

This research aims to enhance the erosion-corrosion durability of monolithic ENP coating used on ductile cast iron. The ENP coating does not usually adhere well to the cast iron surface due to the special characteristics and innertness of the graphite sphere so an electrochemical surface pre-treatment containing a cathodic treatment was implemented to ensure proper adhesion of the coating to the surface. A slurry pot erosion-corrosion test was performed at a linear velocity of 10 m/s for 16 h, and it verified the efficacy of the treatment. Three different heat treatments were carried out on coated samples at 200 °C, 400 °C, and 600 °C. The sample heat-treated at 600 °C exhibited a pseudo-passivation behavior and displayed the best corrosion resistance of 0.1407 μA/cm2. Nonetheless, in erosion-corrosion tests, it was outperformed by other coatings due to the removal of its oxide layer. The heat treatment at 400 °C resulted in the highest hardness of 871 Vickeres and the best erosion-corrosion resistance of 8.8 mpy compared to 11.74 mpy for the as-plated sample and 381.3 mpy for the cast iron substrate.