Advanced particle diagnostic technology has been applied to establish process parameters to deposit high quality nickel based carbide cermet coatings for marine hydraulic applications. The cermet coatings are produced via the kerosene fuelled high velocity oxygen fuel (HVOF) spray process, which uses a hypersonic flame jet to melt and accelerate feedstock particles onto the component surfaces. The traditional 'trial and error' procedure is not technically robust, as well as being costly and time consuming. Instead, a superior method is implemented in the current study that performs real time monitoring of the process parameters associated with the HVOF flame jets. Subsequently, coatings can be produced with the knowledge of the inflight particle size, temperature and velocity profiles. The analytical results allow identification of suitable coating process parameters, which translate to coatings of lower porosity and enhanced mechanical performance.

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Plasma ferritic nitrocarburising of carbon and low alloy 0·4%C steels was carried out at 570°C in a N2–H2 atmosphere containing CO2 gas additions. The influence of the atmosphere composition, the duration of treatment, and the composition and microstructure of the steels on the phase composition of the compound layer was investigated. The formation of a monophase ɛ compound layer was not possible with the parameters used in this study. The phase composition of the compound layer was found to be very dependent on the amount of CO2 in the process gas. A difference in the plasma nitrocarburising behaviour of the two low alloy steel grades was observed, and the formation of some austenite in the diffusion zone of one of the steels, at the interface with the compound layer, is proposed to explain this observation.

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