Investigation into the Biofouling and Corrosion Performance of Carbide Based Coatings, Subjected to Immersion in Australian Coastal Waters
Matthew Leigh, Andrew S.M. Ang, Richard Piola, Wayne Neil, Christopher C. Berndti, Hugo Howse, and Scott A Wade
Hydraulic components are used in numerous maritime applications in which they are exposed to environments that can seriously degrade performance, for example due to corrosion and/or biofouling. In many instances coatings are applied as a protective layer on such components to attempt to mitigate these effects. Previous work has reported that High Velocity Oxygen Fuel (HVOF) technology has the potential to produce carbide based coatings with dense, low porosity microstructures which have good corrosion resistance, high bond strengths and low oxide content. The current studies report on the performance of several types of HVOF coatings to resist biofouling and corrosion whilst also looking at the mechanical properties and evaluating the coatings’ function when used in hydraulic applications. Deployment around the Australian coastline in various marine sites with different climates was chosen to investigate the biofouling and corrosion rates of the HVOF coatings. Documenting growth rates of fouling, taking samples of both water and settlement allowed the closer investigation into any corrosion or biofouling which would impact the surface metrology, in turn putting a hydraulic system at risk of failure. The field tests after twelve months suggest that there are two potential HVOF carbide-based coatings that could be used for marine hydraulic application, particularly when the shaft material is Monel® K500. There were no delamination failures observed for WC-NiCr or WC- Hastelloy® HVOF coatings. The biofouling rate of HVOF coatings was 2-3 times lesser than ? those of the control- plasma spray alumina-titania coatings. Furthermore, a modified ASTM C633 coating adhesion test also indicated no detrimental loss of coating adhesion strength. The surface metrology results also show that the surface roughness of these HVOF coatings did not vary significantly over the field testing trials and is within the specification requirements of a functional hydraulic shaft. Performance in a hydraulic cycling test before and after the immersion period was also done to determine the impact to a hydraulic system’s seals and oil. The presentation will include an analysis of the data, applicability of the HVOF coatings in hydraulic applications and recommendations for future studies.