Experimental Study of Various Low-Friction Coatings for High-Temperature Gas Foil Bearings Under Cold-Start Conditions

This article presents the experimental research carried out on five different materials with which the top foils have been coated. A foil bearing with these foils was tested under different load conditions. The key operating parameters were determined, such as the moment of friction during the run-up and run-down tests as well as the temperature of the top foil. The AS20 coating, like the TiAlN coating, was intact (with the exception of several places where it was worn and where the Inconel sheet was visible) and was suitable for further use. The WC/C coating was damaged in many places, which shows that this type of coating cannot be used in combination with a journal coated with chromium oxide. The foil coated with MoS₂/C had many areas where the coating was worn and also many areas where it was erased completely, so this type of coating was not durable. The use of a combination of TiAlN and MoS₂/C coatings resulted in minor wear of the outer coating (made of MoS₂/C) and the appearance of the inner coating, which is more resistant to abrasion. The tested materials will be used in the future to build a foil bearing resistant to operation at elevated temperatures in a gas microturbine.