In-Depth Microstructural Analysis of High-Performance Nickel Chromium Coating with Complex Composition

Abstract Recently, special types of high-temperature and corrosion-resistant nickel chromium coatings have been designed and applied on industrial equipment and tools. In addition to NiCr, a large number of alloying elements in small amounts are added to the coating composition. In this study, the high-velocity oxygen fuel (HVOF) technology has been utilized to deposit NiCrSiBMoFeCuC as an example of coating with complex composition. The microstructural characterization was carried out on the coating sample using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The coating microstructure exhibited low porosity content approximately 3%, which is in the acceptable range for an anti-corrosion protective coating. The coating exhibited strong adhesion to the substrate, with no evidence of delamination, indicating good interfacial bonding. Notably, a high density of dislocations within the grain core was observed in TEM micrographs. The x-ray diffraction (XRD) analysis of the powder identified the major peaks as expected, but the coating sample showed formation of some extra phases during HVOF process that may alter thermo-mechanical properties of the coating. The need for this study can be justified due to the unique composition of the coating that makes it suitable to be used as protective layer for corrosion protection in harsh environment for industrial parts and components. While the added boron content is expected to enhance the hardness of the coating, silicon may improve the wear resistance of the NiCr coating.