Study of Corrosion Behavior of Conventional and Nanostructured WC-Ni High Velocity Oxy Fuel (HVOF) Sprayed Coatings

Abstract

The current study is focused on WC-Ni cermet coatings, materials that are extensively used in applications requiring wear resistance. In this work, WC-10%Ni powder was thermally sprayed onto mild steel using High Velocity Oxy Fuel (HVOF) spray technique. The nanostructured specimen was produced from sprayed samples by heat-treating at 1100°C in a vacuum chamber. Their structures were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Polarization and electrochemical impedance spectroscopy (EIS) tests were performed on both types of coated samples in 3.5% NaCl solution. The amorphous phase in WC-10%Ni coating was transformed to crystalline phases by heat treatment at high temperatures. Heat treatment of these coatings at high temperature also resulted in partially dissolution of WC particles and formation of new crystalline phases. Generation of these phases produced the nanostructured coating with better mechanical properties. Comparative electro chemical test results showed that, the heat treatment could improve corrosion resistance of the nanostructured WC-10%Ni coating than the as sprayed coatings.