Friction and Wear Performance of Composite SiC-YAG Thermal Spray Coatings in Water-Based Lubricants for Maritime Applications

The tribological performance of four different thermal spray coatings has been tested against five different polymer seal materials in a fully formulated water-based lubricant. Water-based lubricants have been proposed for a marine application due to their environmental acceptability and their potential benefits when they are used in oil-to-sea interfaces minimizing the issues related to seawater contamination. The effect of normal load and speed on friction was studied for all seal-coating candidates. Hydrogenated acronitrile–butadiene rubber (HNBR) and ethylene–propylene–diene rubber (EPR) seals resulted in higher coefficient of friction (CoF) compared to ultra-high molecular weight polyethylene (UHMWPE), aliphatic polyketone (PK) and synthetic woven fabric impregnated with phenolic resin (SWF) plastic seals. This was attributed to the higher real contact area generated by the softer rubber seals compared to the harder plastic seals at the same normal load. From the point of view of the tribosurfaces tested in this work (hardened steel, WC-CoCr, Cr₃C₂-NiCr and SiC-YAG), friction and wear were controlled by two different mechanisms depending on the type of tribosurface. For metallic surfaces, the friction modifiers in the lubricant were adsorbed on the metals and controlled the frictional performance. The hardened steel (100% metallic surface) showed the lowest CoF, followed by the two cermet coatings (21-23 vol.% of metallic binder). The SiC-YAG coating (ThermaSiC) showed the best friction and wear performance due to the formation of a hydrated film on the SiC phase (77 vol.% of the surface) despite not having any metal matrix.