A Comparative Analysis of Microstructure and Mechanical Properties of Cr3C2-NiCr Composite Coatings Deposited by APS and HVAF Techniques

Abstract

The Cr₃C₂-NiCr coating is well-known for its excellent mechanical properties and high resistance to wear/oxidation at elevated temperatures, making it a desirable material for protecting industrial steel components. The quality and properties of the as-sprayed coatings depend on various factors, with the spraying technique being a primary determinant. Atmospheric plasma spraying (APS) is a commonly used method for applying the coating at an industrial scale; meanwhile, high-velocity air fuel (HVAF) spraying is a novel approach known for superior quality and properties of as-sprayed coatings. Despite the advantages of the HVAF method, APS remains the competitive method for coating deposition due to its lower production costs, versatility in applying different materials, and requirements for powder quality and size. These advantages motivate further research and development of spraying equipment/modes for APS. The primary goal of the present work is to improve the quality and competitiveness of Cr₃C₂-NiCr coatings applied by the APS technique utilizing the state-of-the-art Metco TriplexPro-210 gun, in comparison with HVAF as-sprayed coatings by Kermetico C7 gun. The study involves comparing the microstructure and mechanical properties of APS and HVAF as-sprayed coatings. Microstructures were analyzed using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) methods. The XRD results were discussed based on quantitative Rietveld analysis as a guide for altering the carbide content during the spraying process. The assessment of microhardness and its distribution over the coatings were evaluated using the Weibull distribution of Vickers microhardness, while the elastic modulus and plasticity index were evaluated through a depth-dependent test using a Berkovich indenter. Additionally, the tribological properties of the as-sprayed coatings were investigated through a ball-on-disk sliding wear test, measuring the coefficient of friction and wear rate to understand their performance in relation to the coating's plasticity index.