Gas Turbines For Electrical Power Production

High Temperature Solid Lubricant Coatings PS304 Coating Cross-section During start-up and shut down, prior to developing a gas film, sliding occurs between the shaft and top (inner) foil surfaces. Solid lubrication must be provided to reduce friction and wear. Traditional solid lubricants (e.g., graphite, Teflon®) readily solve this problem at low temperature. High temperature operation, however, had been a key obstacle. Without a suitable high temperature coating, foil air bearing use is limited to about 300°C (570°F). A new chrome oxide based journal coating, designated PS300, has been shown to provide good friction and wear properties in foil bearings at least to 650°C (1200°F). Subsequent development of PS304 coating has promise of enabling the turbomachinery foil bearing coating objectives: Provide start/stop wear protection for foil bearings Operate from cold start to 815°C (1500°F) No vaporization or emissions Machineability (Download Accessible GIF Plug-in) NASA PS304 - US Patent No. 5866518 U.S. Patent No. 5,866,518 'Self-Lubricating Composite Containing Chromium Oxide', awarded 2 February 1999 60% NiCr - Binder 20% Cr2O3 - Hardener 10% BaF2/CaF2 - Hi-Temp Lube 10% Ag - Low-Temp Lube Wide temperature spectrum solid lubricant coating PS304 has successfully lubricated foil bearings at high loads for 100,000 start/stop cycles from 25° to 650°C (75° to 1200°F)

PS300 Series Development PS300 was originally conceived & put into practice in early 1995 In '96-'99 work continued on the coating tailoring the composition for various substrate alloys Oil-Free turbocharger with PS304 demonstrated at 95,000 rpm & 650°C (1,200°F) turbine inlet temperature, 17 March 1999 PS300 is fully developed 1st license awarded & 3 others in process

PM300 is being developed (powder metallurgy) Coating Process Development Thermal Spray Technique Evaluation Plasma spray Low pressure plasma spray (LPPS) HVOF Environmental Durability 1000's of hours of exposure Microstructural changes Environmental effects (air vs. inert) Coating Adhesion Enhancement Surface treatment Interfacial binder layers Adhesion testing Processing Steps Plasma spray coating is a well established thermal spray process in which the powder form of the desired coating material is injected into an electrically ionized Argon plasma in a plasma spray gun. The injected powders melt and are accelerated onto the substrate to be coated. Substrate preparation typically consists of undercutting the surface to accept the coating (usually 0.005-0.010" thick). The coating is oversprayed and then finish ground to achieve a specified or desired surface finish and dimension. Plasma sprayed coatings can be polished or put into use in the as ground condition. Porosity levels are low, typically less than 15%. Following repeated rubbing contact, wear debris often "fills in" surface pits and voids yielding mirror smooth surfaces. Undercut shaft Sandblast finish Plasma spray Finish grind After initial use

Success Stories PS304 coating enabled demonstration of first Oil-Free turbocharger PM304 used by ADMA Products, Inc. to manufacture high temperature bushings as bronze replacement for Lincoln Electric furnace conveyor system PS304 successfully lubricates steam turbine control valves for Elliot Turbines

Suppliers Hohman Plating (licensee for PS300 coating application) ADMA Advanced Materials (licensee for PS/PM300 powder and powder metallurgy bushing production) Reports Performance and Durability of High Temperature Foil Air Bearings for Oil-Free Turbomachinery, NASA/TM-2000-209187/REV1, Mar 01, 2000 Particle Size Effects on Flow Properties of PS304 Plasma Spray Feedstock Powder Blend, NASA/TM2002-211550, May 2002 Effects of Humidity on the Flow Characteristics of PS304 Plasma Spray Feedstock Powder Blend, NASA TM-2002-211549, May 2002 Particle Morphology Effects on Flow Characteristics of PS304 Plasma Spray Coating Feedstock Powder Blend, NASA/TM-2002-211206, January 2002 -------------------------------------------------------------------------------Note: The listings on this page do not constitute an endorsement by the Federal Government (also see the NASA Website Disclaimer Statement). Rather, they are used as a means to foster greater dissemination of information and use of foil bearing technology. Companies wishing to be added should contact the web page curator shown below. -------------------------------------------------------------------------------Responsible NASA Official: Dr. Christopher DellaCorte Curator: Michelle L. Beagle Last Update: April 7, 2008 Web Privacy Policy and Important Notices