Performance Evaluation of Thin Cermet Coatings Produced by HVAF Spray: A New Approach for Hard Chrome Replacement

The electroplated chrome is a hard and wear-resistant coating and, therefore, is widely accepted in several applications. But due to its carcinogenic nature there is a demand for an alternative method to replace the hard chrome plating with a comparable or superior wear resistance but crack-free coating. Furthermore, deposition of thin coating with industrially acceptable surface roughness is economical as it requires less powder and elimination of several grinding processes. In the present study, synthesis of thin hard coatings of WC-10Co-4Cr by high velocity air fuel spraying, as an alternative to hard chrome plating is being explored using a specific particle size range. Thin coatings were deposited with multiple torch options and by employing different nozzle sizes. The objective was to understand the role of varied combustion heat flux and velocity components on the overall thin cermet coating characteristics. Detailed microstructural characterization was performed to correlate the sliding wear performance of the as-sprayed thin coatings with the phase characteristics. Further, a comparative study has been made with respect to the hard chrome plating in order to assess the performance of the as-sprayed thin cermet coatings. The obtained results indicated that the surface roughness of the as-deposited thin thermal sprayed WC-10Co-4Cr coatings is an order of magnitude higher than that of hard chrome plating, but it is less when compared to coatings deposited using conventional particle size range. Further, the advantages of using fine powders include reduced porosity and crack free deposits. In this direction, the outcome of the present study is expected to provide insights about the optimum thermal energy required without excessive surface melting and/or oxidation while retaining the dense microstructural features through sufficient kinetic energy for enhanced wear resistance.