Comparison ofSeveral Different Sputtered Molybdenum Disulfide Coatings forUseinSpaceApplications RobertL.Fusaro_andMarkSiebert_ Abstract Tribology experiments ondifferent typesofsputtered molybdenum disulfide (MoS2) coatings (obtained fromdifferent vendors) usingaccelerated testing techniques wereconducted. Thepurpose wasto determine whichwouldbethebestcoating forusewithauxiliary journal bearings forspacecraft energy storage flywheels. Experiments wereconducted inmoistair(50%relative humidity) andindryair(<100 PPMwatervaporcontent) onaPin-on-Disk Tribometer todetermine howwellthecoatings wouldperform inair.Experiments werealsoconducted onaBlock-on-Ring Tribometer indrynitrogen (<100PPMwater vapor)tosimulate howwellthecoatings wouldperform invacuum. Friction, counterface wear,coating wear,endurance lifeandsurface morphology wereinvestigated. Introduction NASAGlenniscurrently developing magnetic bearings tobeusedforlevitating energystorage flywheels fortheInternational SpaceStation andforsatellites. Toinsuresafety(ifmagnetic bearings shouldfail) andtoprevent damage from"bumps," mechanical auxiliary bearings mustalsobedeveloped forthis application. Several different typesofmechanical bearings arebeingconsidered aswellasseveral different lubrication systems. Ifsolidlubricants areselected, theonewiththelongest endurance lifewith reasonable frictionandwearproperties inavacuum environment isthemostdesirable. However, many oftheMoS2basedlubricants beingconsidered donotworkwellinambient air.Itispossible thatexposure ormishandling inairmightreduce thelifeorperformance solidlubricant usedforanauxiliary bearing. Thusitisdesirable tochoose asolidlubricant thatworkswellunderallenvironmental conditions. Sputtered MoS2coatings werechosen forthisstudybecause theyhavebeenshowninmanyprevious studies tobeexcellent lubricants inavacuum environment [1-7].Theproblem isthatMoS2oxidizes inair [8-15]andcanleadtodamage tothecoatings beforetheyevengetintospace. Recently, newsputtered UoS2coatings havebecome available andhavebeentested[16-20] thatareco-sputtered withvarious materials thatimprove theirperformance inair. Inordertohelpdetermine whichofthesecoatings mightbethebestforthisapplication, anaccelerated testingprogram wasdeveloped toevaluate theirtribological properties ofthesecoatings underdifferent environmental conditions. Thispaperdealswithtribological accelerated testsonseveral different sputtered molybdenum disulfide (MoS2) coatings ina50percent relative humidity (-10,000 PPMmoisture content) airatmosphere andinaverydryairatmosphere (<100PPMmoisture content) usingaPin-onDiskTribometer. Inaddition, thesamecoatings werealsoevaluated inadrynitrogen atmosphere (<100 PPMmoisture content) usingaBlock-on-Ring Tribometer tosimulate avacuum condition. Materials Sixdifferent sputtered MoS2 coatings wereevaluated thatweresupplied from5different vendors. Table1 liststhevendors andtheadditives inthefilms.Thecoatings wereapplied tothedisksofthePin-on-Disk Tribometer andtotheringsoftheBlock-on-Ring Tribometer. AfewBlock-on-Rings testswerealso conducted withblocksthatwerecoated withtheCSEM-Ti orCSEM-AI coating. Thedisks,blocksand ringsusedinthisstudyweremadeof440Cstainless steelwithaRockwell hardness ofC-57toC-59.The diskswerelappedandpolished toasurface finishof0.040_+0.015#mcenterline average (CLA).Instead ofusingpinsinthePin-on-Disk Tribometer, thepinholderwasmodified toholdandconstrain fromrolling NASAGlennResearch Center, Cleveland, OH _*University ofToledo, Toledo, OH Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 305