_i_ /,,,.LL,- WearandCorrosion Resistant PMToolSteelsforAdvanced Bearing Applications B.Hann*,P.Kilonsky*, D.Smith** andM.Sperber* Abstract Aneedexistsfornewbearing materials thatpossess properties notattainable withconventional bearing materials suchasM50,52100,and440C.Thesematerials musthaveacombination ofthefollowing: high attainable hardness, highhothardness, dimensional stability athightemperature, wearresistance, corrosion resistance, toughness, androllingcontact fatigue resistance. WithPowder Metallurgy (PM) technology, higheralloycontents withgreater volume fractions offine(<5pro)primary carbides maybe achieved, without theadverse segregation inherent inconventional materials. Various PMalloymaterials areindevelopment toaddress thecurrent andfutureneedsofthebearing users. Several papers havebeenpublished discussing CPM®VIMCRU®20TM,acobalt-free PMhigh-speed steel,whichhasexhibited somesignificant property advantages compared toM50and52100. Though CPM®VIMCRU®20TMshowspromise formanybearing applications, theneedforahighhardness, corrosion resistant bearing material hasyettobeaddressed. Several highhardness, corrosion resistant PMtoolsteelshaverecently beendeveloped. Newmaterials havebeendeveloped withcorrosion resistance properties comparable tocommercially available bearing gradestainless steels, butwith substantially improved wearresistance. Introduction Anissuethatstillexistsfortheaerospace designer istheneedforacorrosion resistant material thatmay beusedtoproduce criticalbearings requiring highhardness, dimensional stability, andtoughness. More andmoreaerospace bearings areoperating inamoreopenenvironment thanwasrequired inprevious designs. Insomeinstances, bearings arenotonlyexposed tohardabrasives inthelubricating media,but alsotocorrosive attackbymoisture, acids,orlubrication breakdown constituents. Asecondary, butequally important issuethatneedstobeaddressed isshelflife.Aconventional bearing material maybesuitable foragivenapplication, butoftencorrosion takesplacewhileininventory that precludes thematerial frombeingusedforitsintended application. Corrosion resistant bearing materials exist,buttheattainable hardness, andtherefore compressive strength andwearresistance, arenot equivalent totheirconventional counterparts, like52100orM50.Bearing candidate materials with excellent corrosion resistance, goodtoughness, andhardness levelgreater than62HRchavebeen developed. Employing thesameprinciples usedtodevelop CPM®VIMCRU®20TM,thePMprocess hasbeenapplied todevelop anewadvanced bearing material thatisbothwearandcorrosion resistant. Background PMmaterials havebeensuccessfully commercialized fornon-corrosive bearing environments. CPM®VIM ® TM CRU20,avacuum induction melted(VIM)version ofM62high-speed toolsteel,hasbeendiscussed invarious papers [1-3].CPM®VIMCRU®20TMhasexhibited rollingcontact fatigue lifecomparable to siliconnitrideandsuperior toconventional bearing grades, likeM50andM50NiL [1].CPM®VIMCRU® 20TMhasalsobeenusedinbearing raceways withsiliconnitrideballs,toprovide forahybridbearing design withhigherloadcapacity andlongerlifethan52100[2,3].Currently fourlifetestsofReaction Wheels andControl Moment Gyroscopes arerunning usingthesehybridbearings. OneoftheCMGtests *Crucible Compaction MetalsDivision, Oakdale, PA **Honeywell Satellite Systems Operation, Phoenix, AZ Proceedings ofthe35thAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 139