A new technology to synthesize thin hard surface coatings by high velocity air fuel spray has been developed as an eco-friendly safe alternative to hard chrome plating used on various car parts, instruments and kitchen utensils. Has the potential to emerge.
Chrome plating is used because it is hard and wear resistant as a coating. However, it contains chromates, fluorites and hexavalent chromium which make it carcinogenic in nature. Now researchers have begun a search for a safe, eco-friendly alternative with equivalent or better resistance but crack-free coating. Deposition of thin coatings with industrially acceptable surface roughness is economically advantageous because there is less powder and many grinding processes are unnecessary.
Thermal spray is a group of techniques for depositing a variety of coatings to reduce wear and improve corrosion resistance during various industrial applications. Whereas with conventional thermal spray techniques, the layer thickness build up becomes higher and then processes like grinding and polishing have to be done multiple times to achieve the required thickness and roughness. A new technology called High Velocity Air Fuel (HVAF) which involves low temperatures and high particle velocities can deposit layers (coatings) using fine sized powders (5-15 µm).
Scientists at the International Advanced Research Center for Powder Metallurgy and New Materials (ARCI), an autonomous institute of the Department of Science and Technology (DST), have prepared alloy of tungsten, cobalt and chromium (WC-10Co-4Cr) by high velocity air fuel spraying. Synthesized thin hard coatings of. Thin layers were deposited using torches of different capacities and different nozzle sizes.
These coatings were obtained on stainless steel substrates with 50 µm thickness and surface roughness close to 1.5 µm. The type of torch and nozzle design significantly influenced the properties of the coatings. Better sliding wear performance was observed with HVAF sprayed thin WC-10Co-4Cr compared to conventional hard chrome plating (HCP). Similarly, corrosion studies conducted on the coating and comparison with HCP revealed that the new technology could be a better alternative to HCP for heavy load applications such as hydraulic shafts, valves, piston rods, balls, etc.
A comparison of hard chrome plating with as-spread thin ceramic-containing thermal resistant (cermet) coatings to assess the performance of the latter revealed that the thin thermally spread WC-10CO-4Cr coatings thus deposited The surface roughness is an order of magnitude higher than that of hard chrome coatings.
Additionally, the coating can be deposited in a machined condition to obtain a smooth surface and coating thickness of approximately 50 microns. This greatly reduces post-coating finishing operations resulting in significantly reduced processing and raw material costs with superior coating resistance compared to HCP.
