Wide range of thermal sprayed coatings applied in the basic industries with different combinations of coating substrate material are used for applying protective coatings to material surfaces as no other technology of coating deposition offers. HVOF is one of such technologies, which involves the deposition of molten or semi-molten droplets of powder onto a substrate to form a coating. It is found that this technique forms coatings with very small porosity (<2 %) and high adhesion strength (> 80 MPa). Recently this coating technique is often considered as a best alternate for the replacement of traditional electrolytic hard chrome (EHC) plating which pollutes the environment and has serious environmental and health concerns causes lung cancer by toxic hexa-valent Cr6+. The HVOF sprayed WC-based cermet hard coatings such as WC–Co, WC–Co–Cr have been investigated for obtaining the coatings of high hardness, wear resistance, thermal stability and corrosion resistance. Ni–Cr and other additives such as B, Si, W, Fe, and Mo can also be applied to protect steel articles. The tribological properties of part surfaces like wear, frictional force at the room and at higher temperatures is a serious problem occurring in many of the machine components like aircraft, automobile and metallurgical industries. One of the most serious problems of industries is corrosion which causes damage in billions of dollars each year. Materials are very often exposed to environments wherein the metallurgical reaction between the environment and the materials that are corrosive can affect the lifetime of the components and produce high maintenance costs.
Substrate selected for the application of the coatings was mild steel. Roughness of substrates prior to HVOF deposition is required, as a means of improving the mechanical bonding of the coating, the substrate material was cleaned with isopropyl alcohol followed by grit blasting with coarse Al2O3-24mesh.
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