LessonsLearned Measurements oftheCOFbetween common spacemechanism materials haveshowntheimportance of considering thecomposition ofthesurfacelayerwhenanalyzing theperformance ofamechanism. We havealsoshownthatthemechanism environment duringtesting,storage, andoperation canexerta stronginfluence ontheCOFbetween thecomponent materials. Tosummarize, forthematerials testedinthisstudywehavefoundthat: •TheinitialCOFatametal/metal interface waslessthanhalfofthesteadystatevalue,asthesurface oxidesandcontaminants werewornaway. •TheCOFbeforeandafterwearremoval ofametaloxideinairwasapproximately twothirdsofthe COFinvacuum. •TheinitialCOFatametal/unburnished-solid-lubricant interface wasfourtimesthesteadystateCOF because theMoS2wasnotyetpresentatthephenolic bindersurface. •TheCOFatametal/solid-lubricant interface wasgreaterinthepresence ofairduetothelesser lubricating qualities ofoxidized MoS2. Theextentofthisdifference wasdependent uponload. •TheCOFatametal/solid lubricant interface inairdepended upontheappliedload. •TheCOFneartheinterface between asolid-lubricated regionandacleanmetalsurfacecan decrease afterveryfewcyclesduetothetransferoflubricant duringslidingacrosstheinterface. •Onlyasmallamountoftransferred lubricant wasnecessary toreducetheCOF,andthesesmall amounts weredifficulttoremovebywipingwithsolventsaturated wipes. •Asmallamountofoilcontamination decreased theCOFbymorethan50%duringthefirstseveral cycles. Theseobservations underscore thesignificance ofobtaining anaccurate andreliablequantityforthe COFthatisvalidforthespecificapplication environment. ItisevidentthattheCOFbetween oxidized materials mayvaryremarkably fromthequantitydetermined forcleanmaterials, andtheCOFcan dependsensitively onthetestingorapplication environment. Thus,whenanapplication allowsforonlya narrowdistribution offrictioncoefficients, itisimperative tocarefully scrutinize thevariability oftheCOF withtheconditions ofthetesting,storage, andapplication. Furthermore, weassertthatquantification of thisenvironmental variability canonlybeobtained empirically. Inpractice, attention mustbegiventothesurfacecomposition duringstorageandtesting.Forexample, whenalubricant hasbeenappliedintheproximity ofaregionwherehighfrictionisrequired, aminimum numberofdevicetestsshouldbeallowedtoreducethetransferoflubricants toothersurfaces (particularly inair,wherethespreadismoreeffective). Bycontrast, inasituation whereabondedfilmis appliedtoprovideaminimum COF,alargenumberoftestsmaybedesiredtoburnishaweartrackinthe film.Finally,attention mustalwaysbegiventotheproperties oftheoxidized materials, whichare ubiquitous untilwornawayinvacuum. References 1.Buckley, D.H."Surface EffectsinAdhesion, Wear,andLubrication." ElsevierScientific, NewYork, NY,1981. 2.Singer,I.L."SolidLubrication Processes," inFundamentals ofFriction,Macroscopic and Microscopic Processes, Singer,I.L.andPollock, H.M.(eds.)pp237-261, Elsevier, Amsterdam, 1992. 3.McMurtrey, E.L."HighPerformance SolidandLiquidLubricants: AnIndustrial Guide." NoyesData Corporation, ParkRidge,NJ,1987. 4.Claus,F.J."SolidLubricants andSelfLubricating Solids"Academic Press,NewYork,1972. 5.Peterson, M.B.andJohnson, R.L."Friction andWearCharacteristics ofMolybdenum Disulphide. I. EffectofMoisture." NACA-TN-3055, 1953. 6.Fleischauer, P.D.andBauer,R.,"TheInfluence ofSurfaceChemistry onMoS2Transfer Film Formation," ASLETrans.,30(1987),160-t66. 33O