Theresultsofthefirsttest,notshownhere,indicatethatthefrictionontheinitiallyunlubricated sideofthe diskdoesnotappeartobereducedbyeffectivelubricanttransferundertheselowerloadconditions. In particular,thefrictioncoefficients stayhighontheunlubricated portionofthedisk,regularlyexceeding1.0 overthecourseofthetest.However,frominitialtestmeasurements, itdoesappearthatsomereduction infrictionisevidentnearthecrossoverpointfromthelubricatedtotheunlubricated sideofthedisk.The effectisnotnearlyasdramaticasthatobservedathigherloads,consistentwiththepremisethatlower loadswouldbelessefficientattransferring lubricantundertheconditionsstudied.Thetransfereffectwas moreobviouswiththetestsconductedinair,whichmightalsobetrueunderthelowloadconditions. Thefrictionofacleandiskunderthe0.3Nloadshowedthatthefrictionundertheseconditionsremains fairlylowthroughoutthefirst8softhetest.Infact,theaveragefrictioncoefficientdetermined fromthis onetestwas0.47,avaluethatismuchlowerthanthe0.74obtainedearlier.Thisresultmostlikely occursbecauseofthelightloadsusedinthisparticulartest.Thesurfaceoxidelayerswouldhaveamore prolongedeffectunderlowerloadconditions,astheywearawaymoreslowly. OilContamination Tests Surfacecontaminants havethepotential ofchanging thefrictioncoefficient inamechanical contact. In thepresentcase,weinvestigated theeffectofcontamination byathinfilmofanesterpumpoil.Thisoil wouldbeexpected toalterfrictionifitexistedinlargeenoughquantities. Weareexploring theextentto whichasmallamountofoilcontamination impactsthefrictioncoefficient. RecallFigure8,whichpresents theinitialfrictionmeasurement obtained inaironaclean, uncontaminated 440C/superalloy pair.Theseresultsshowedthattheaverage, steadystatefriction coefficient forthiscombination inairwasapproximately 0.56,andthatthefrictioncoefficient onthevery firstrevolution undersimilarconditions wasapproximately 0.2-0.25. Thefrictionisobserved toincrease witheachsuccessive revolution, achieving theexpected average valuesafter3to5revolutions. Figure13andFigure14,presentthesamematerial paircoatedwithoilfilmsof15nmand60nm thickness, respectively. Thesefiguresdemonstrate theoilcontamination effectsonthefriction.As expected, wefoundthattheinitialfrictionwiththeoilfilmpresentislowerthanthefrictionobtained onthe cleansurface. However, thesignificant conclusions tobedrawnfromthisdataarethattheinitialfriction coefficient waslessthanhalfofthesteadystatevalue,andthatthiscondition persisted formanycycles. Specifically, onthe15nmfilm,thefrictioncoefficient isintherangeof0.15to0.20forthefirst3-4cycles, thenincreases tovaluesapproaching nominallevelsafter2to3morecycles.Inaddition, duringthefirst fewcycles,thenoiseinthefrictiondataismuchreduced, aswouldbeexpected fromalubricated contact. Theseeffectsareevenmorepronounced inthedatafromthe60nmfilm.Thislowerfrictionisalogical extension ofwhatwasobserved inthe15nmdata,andshowsthatfilmsinthisthickness regimewill impactthefrictioncoefficient, potentially bringingittovaluescloseto-0.1.Somescatteriscertainly tobe expected intheseresultsbecause theuniformity ofthefilmcoatingcannotbeguaranteed andbecause thickercoatings inareaswherethetestwasrunningwouldleadtolowerfrictionandmorepersistent low friction.Atlongertesttimes,thefrictionvaluesdoreachthoseexpected forthecleanmaterials, presumably afterthelubricating surfacelayerhaswornaway.Experiments conducted withavaryingload regimen showedsimilarresults,withfrictioncoefficients andnoiselevelsgreatlyreduced earlyinthetest, followed byhigherandmoreerraticfriction. 328