New Delhi: A groundbreaking method for synthesizing thin hard surface coatings through high-velocity air fuel spraying is poised to emerge as a safer, environment-friendly alternative to conventional hard chrome plating. Chrome plating, known for its hardness and wear resistance, contains carcinogenic elements, necessitating the quest for a safer alternative with equivalent or superior wear resistance and crack-free coating.
Researchers, spearheaded by scientists from ARCI, an autonomous institution under the Department of Science and Technology (DST), have successfully utilized high velocity air fuel (HVAF) spraying to deposit thin coatings of a composite alloy of Tungsten, cobalt, and chromium (WC-10Co-4Cr). Unlike traditional hard chrome plating (HCP), which poses environmental risks, the HVAF technique involves low temperatures and high particle velocities, enabling the use of finer-sized powders (5-15 µm).
The thin coatings achieved a thickness of 50 µm with surface roughness close to 1.5 µm on stainless steel substrates. The choice of torches with different capacities and nozzle sizes significantly influenced the properties of the coatings. Superior sliding wear performance was observed with HVAF-sprayed thin WC-10Co-4Cr coatings compared to HCP. Additionally, corrosion studies demonstrated the new technique’s potential as a superior alternative for heavy-load applications such as hydraulic shafts, valves, piston rods, and balls.
Comparisons between hard chrome plating and as-sprayed thin cermet coatings revealed that the as-deposited thermal sprayed WC-10Co-4Cr coatings exhibited a surface roughness an order of magnitude higher than hard chrome plating. Remarkably, the new coatings can be deposited on as-machined surfaces to achieve a smooth surface with approximately 50 µm thickness, significantly reducing post-coating finishing operations and associated costs, while offering better wear resistance than HCP.
Published in the Journal of Thermal Spray Technology, the study is expected to provide crucial insights into optimizing thermal energy requirements, ensuring dense microstructural features for enhanced wear resistance without excessive surface melting or oxidation. This breakthrough marks a significant step toward a safer, eco-friendly alternative in surface coating technologies.