Analysis of microstructure, mechanical indentation and corrosive behavior of a thermally sprayed NiFeCrBSi-WC composite coating

Extending the lifetime of drilling bits primarily requires an in-depth understanding of the material's behavior from which they are made. Metal matrix composite coatings (MMCs) are mostly used to cover these industrial components to increase their efficiency and protect them from corrosion and wear. For the drilling bits, the best combination of characteristics can be assured through the design of an efficient multiphase metal matrix composite coating. Among these materials, nickel-based composites have been recently raised as alternatives to chromium and cobalt-based ones. This paper aims to unravel the underlying relationships between the microstructure and the mechanical indentation behavior and electrochemical response of thermally sprayed nickel-based composite coating. For that, a nickel-based composite coating is characterized. This coating was separately obtained after flame spraying of NiFeCrBSi feedstock wires by using acetylene as a fuel. The coatings were deposited in air on X18 carbon steel substrates. Our results reveal that the matrix of the coating mainly contains Ni-γ dendrites. The interdendritic space of the coating is filled withγ-Cr2.4W0.6Si eutectic. In this coating, The Ni- γ phase that represents a eutectic constituent is depleted in iron. The morphology of carbides differs from one precipitate to another. The indentation behavior differs depending on the elasto-plastic behavior of the present phases and the presence of voids. Moreover, the EIS curves proved that the increase in ion concentration augments the charge transfer at the coating/electrolyte interface and accelerates corrosion. In the sulfuric solutions, the coatings form a thin and compact passive film layer that makes the charge transfer permanently constant at high ion concentrations (35 g/l).