In the pursuit of safer and environmentally friendly alternatives to hard chrome plating, researchers have unveiled a groundbreaking technique for synthesizing thin, hard surface coatings. This innovative method utilizes high-velocity air fuel spraying (HVAF), offering a potential solution for applications ranging from car parts and tools to kitchen utensils.
Traditionally, chrome plating has been favored for its hardness and wear resistance. However, the presence of carcinogenic elements like chromates, fluorites, and hexavalent chromium has spurred a quest for alternatives with comparable or superior wear resistance and a safer composition. Enter HVAF, a novel thermal spray technique that operates at low temperatures and high particle velocities, allowing for the deposition of crack-free coatings using finer-sized powders (5-15 µm).
Researchers at the Autonomous Research Centre for Innovations (ARCI), a department under the Indian Department of Science and Technology (DST), spearheaded the synthesis of thin hard coatings using a composite alloy of tungsten, cobalt, and chromium (WC-10Co-4Cr) through HVAF spraying. The process involved employing torches with varying capacities and different nozzle sizes to achieve coatings with a thickness of 50 µm and surface roughness close to 1.5 µm on stainless steel substrates.
The properties of the coatings were significantly influenced by the type of torch and nozzle design used. Superior sliding wear performance was observed in HVAF-sprayed thin WC-10Co-4Cr coatings compared to conventional hard chrome plating (HCP). Corrosion studies further validated the viability of this new technique for heavy-load applications such as hydraulic shafts, valves, piston rods, and balls.
Comparisons between hard chrome plating and as-sprayed thin cermet coatings demonstrated that the surface roughness of the as-deposited thermal sprayed WC-10Co-4Cr coatings was an order of magnitude higher than that of hard chrome plating. Additionally, these coatings could be deposited on as-machined surfaces to achieve a smooth surface with approximately 50 µm thickness, reducing the need for extensive post-coating finishing operations.
The findings, published in the Journal of Thermal Spray Technology, are expected to shed light on the optimum thermal energy required for enhanced wear resistance without inducing excessive surface melting or oxidation. This research not only presents a greener alternative to hazardous chrome plating but also promises significant cost reductions in processing and raw materials through minimized post-coating finishing operations. The HVAF synthesis technique emerges as a promising avenue for industries seeking both performance and environmental responsibility in surface coatings.