Robust Solid Lubricant Coating for Gears of Cryogenic Fuel Turbopumps

Several advanced solid film lubricant coating processes are evaluated to be used for turbopump gears operating at high speeds and high contact pressures in an RL-10 rocket engine at cryogenic temperatures. Based on existing application data concerning the performance of the proposed advanced coatings a significant improvement in turbopump gear operation is expected. Improvements in coating uniformity, structure, wear life with a reduction in friction and vibrations yield improved turbopump operations. This study details specific characterization and cryogenic testing at appropriate loads and speeds similar to that of rocket fuel pump. Characterization includes microscopy, metallurgy and surface characterization. Cryogenic WAM testing is used to provide the proper tribological test conditions. Coating compatibility with liquid hydrogen is investigated. Advanced coatings include PVD, Spray, Burnish and Smart Surface Laser Textured solid film lubes and Soft Metallic coatings by PVD and Hybrid PVD. We deliver a reference database of the various coating properties and test results of the surface treatments as well as recommendations for treatment of the RL-10 turbopump gear based on our results with deliberate concern for economic industrial viability. Additionally we deliver a robust storage method for treated samples and gears which insures full protection from terrestrial coating degradation primarily caused by oxidation during storage, pre-assembly and ground transportation.