NASA's Glenn Research Center has developed high-temperature solid lubricant materials suitable for foil gas bearings that enable the commercialization of a broad array of revolutionary oil-free gas turbines, compressors, blowers, motors, and other rotating machines that can operate from cryogenic to redhot temperatures. These tribological (friction and wear) coatings and composite powder metallurgy material innovations have immediate and proven spinoff potential for high-temperature steam turbine control valves, exhaust gas recirculation (EGR) valves, articulating ducts and piping joints, and other industrial and aerospace applications.
Oil-free foil bearings require innovative approaches to solid lubrication for start-stop sliding contact that occurs before the gas lubricating film forms. The PS300 and PS400 coatings and their powder metallurgy cousins are composites from a unique combination of metals, ceramics, and solid lubricant additives. Plasma spray coating deposition is used to apply a thick (0.010-inch) layer onto a metal surface that is then ground and polished before use. During rubbing contact, the lubricant phases migrate to the surface, forming a lubricious glaze that prevents wear and reduces friction.
Powder metallurgy techniques are used to make freestanding, self-lubricating components such as bushings and wear plates whenever a coating is not convenient or possible (e.g., inside small-diameter parts). These materials are made from thermochemically stable, nonsoluble, nontoxic constituents, and typically include nickel, molybdenum, chrome oxide, silver, and barium fluoride-calcium fluoride eutectic. Compositions can be easily tailored for specific applications. Operation of machinery using these tribo-materials has been proven over decades of use from subfreezing to over 650 °C.