The Investigation of Support Effect from Hard Substrate to Soft Coating of Pi/Ep-Ptfe Under Different Coating Thicknesses and Frictional Contacts

Abstract

The engine bearings of ships may fail quickly under extreme working conditions, for example, seawater will enter the engine compartment when the ship encounters reefs or is attacked by missiles. To improve the self-lubrication and anti-wear properties of these bearings, a composite coating consisting of ZrO2-PI/EP-PTFE was designed. This coating was prepared using liquid spraying technology on the surface of A370 aluminum alloy, CuPb22Sn2.5 copper alloy and 15# carbon steel, respectively. Three different coatings under 20 μm, 30 μm and 40 μm were sprayed onto the three substrates. The tribological properties of these coatings on the three substrates were investigated under dry sliding wear and seawater corrosion conditions. The results showed that the tribological properties of these coating are influenced by the hardness of this coating, frictional contacts and the support effect of the substrate. The hardness and elastic modulus of the coatings decreased with an increase in coating thickness. The thicker the coating is, the less the support effect of the substrate will be. The adhesive wear of these coatings under dry sliding wear on these different substrates are presented. The CoFs (Coefficients of Friction) of these coatings on all three substrates increased with coating thickness. In contrast, wear rates decreased in accordance with an increase in coating thickness. The hardness of the coating was influenced by the support effect from the substrate. The main factors governing the tribological performance of the coating under dry sliding are the pinch action of the hard grinding ball against the soft coating on the hard substrate and contact pressure. Abrasive wear, spalling wear, plough grooves and spalling pits are observed under seawater corrosion conditions. These findings indicate that greater coating thickness is associated with lower CoFs and wear rates. Seawater corrosion and the scouring effect of high-frequency reciprocating friction are the main reasons.

Keywords: Coating thickness, Frictional contacts, Substrate support, Frictional behavior, Wear mechanism