Fretting behavior of the AISI 304 stainless steel under different atmosphere environment

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FrettingbehavioroftheAISI304stainlesssteelunderdifferentatmosphereenvironments

M.Estevesa,n,A.Ramalhoa,F.RamosbaCEMUC,UniversityofCoimbra,Coimbra,Portugal

bHufPortuguesa,Tondela,Portugal

articleinfoArticlehistory:Received7October2014Receivedinrevisedform19November2014Accepted10February2015Availableonline3March2015Keywords:FrettingWearOxidativeEnergyabstractTheresponseofhomologouspairsofAISI304stainlesssteeltofrettinginvariousconditionswasstudiedonalinearreciprocatingtribometerwithsphere-on-flatcontact.Thestudywasfocusedonthebehaviorofthecontactunderdifferentatmospheres(nitrogenandoxygen),displacement(20–60mm)andrelativehumidity(10–85%).Evolutionwasassessedbyfrictionandfriction-dissipatedenergyregardingthewear,measuredby3Dprofilometryandopticalmicroscopy.TheoxidationrateswerealsoevaluatedbySEMandRamanspectroscopy.Atmospherecompositiondirectlyinfluencestheoxidationprocess,consequentlythefrettingregimesandwear,althoughthenatureoftheoxidesisdefinedbytheavailabilityofO2andH2O.&2015ElsevierLtd.Allrightsreserved.

1.IntroductionLossofmaterialisoftenassociatedwiththespecificphenom-enoncausingsaidmaterialremoval,usuallyfretting,sliding,roll-ingandimpact.Allofthesecanbecategorizedasacombinationofwearmechanisms,includingabrasive,adhesive,flow,fatigue,corrosive,meltanddiffusivewear[1].Thefrettingphenomenon,mainlygovernedbyvibrationslidingandoneormorewearmechanisms,isoneofthemaincausesoffailurebetweenmatedsurfacessubjectedtovibration.Itischaracterizedbytherelativemovementbetweentwosurfaces,typicallyintherangeofmicrons,dependingonthedimensionsofthematedsurfaces.Thewornsurfacecausedbythistypeofwearissimilartothecontactinterfacegeometrywithdirectionalitymarks[2].Relativemovementscausingfrettingaredivided,usually,intofourtypesofdisplacement,thesebeingtangentialfretting,radialfretting,rotationalfrettingandtorsionalfretting[3–5].Tangentialfrettingconsistsofaunidirectionallinearrelativemovementoftwomatedsurfaces;radialfrettingistypicallyanormal/compressingloadvariationinducedmovementthatalterstherealcontactsurfacebetweensurfaces;rotationalfrettingconsistsofrotationwithanaxisperpendiculartotheappliedloadofonebodyoveranotherwithoutbreakingthecontact(accom-modationofthecontactconditions,ballbearings);andtorsional

frettingischaracterizedbyarotationofonebodyoveranotherbutwheretherotationalaxisiscoincidentwiththeappliedload(spinning).Itshouldbenotedthateverydisplacementisoftheorderofmicrons(verysmallcomparedwiththecontactsurfaces),andcontactisalwaysmaintainedonaspecificzoneandisalwaysareciprocatingmotion[3–5].Frettingregimescanbedividedintopartialslip,grossslipandmixedslipregimes.Thepartialslipregimeisviewedasasmallslidingarea(peripheries)andalargestickingarea(center)inthecontact,resultinginclosedcyclesoffrictionforceversusdisplace-mentplots(frettingcycles).Thegrossslipregimeisthemajorityortotalslidingareaofthecontactandresultsinopencyclesoffrictionforceversusdisplacementplots.Themixedslipregimeisacombinationoftheprevioustworegimes,asaresultofthechangeinthecontactconditionsduringthetest[5].Itisestablishedthatfretting,asafrictionprocess,isgovernedbythecombinationofcontactconditions(tribo-systemcharacter-istics)andnotonlybymaterialproperties[6].Theseconditionsincluderoughness,tribologicallytransformedfilms,environmentconditions,frictionparameters,contactconditionsandmechanicalproperties.Frictionparametersareusuallydefinedbythetypeofapplica-tionineachsystemonworkingconditions,dependingonappliedload,relativedisplacement,andthefrequencyofthemovement[7–9].Also,theinfluenceofthevariationineveryoneoftheseparametersisalsodependentonsystemcharacteristics.Theinfluenceofroughnesshasbeeninvestigatedinanumberofstudies[7,9–11]andtheinfluenceofthisparameteronwear

ContentslistsavailableatScienceDirectjournalhomepage:www.elsevier.com/locate/tribointTribologyInternational

http://dx.doi.org/10.1016/j.triboint.2015.02.0160301-679X/&2015ElsevierLtd.Allrightsreserved.

nCorrespondingauthor.Tel.:þ351239790736.

E-mailaddress:miguel.esteves@student.dem.uc.pt(M.Esteves).

TribologyInternational88(2015)56–65andthecoefficientoffrictionisobvious,suggestingthattheworkenvironmentshouldbeafactorintheallowedtopographictolerances.Amechanicalpropertythatisknowntoinfluencethefrettingbehaviorishardness,whichshouldbehighwhenitcomestomaintainingasinglecomponent.Thiscannotbetruewhenthecontactiscomposedofmultiplehardsurfacesandthegoalistokeepallcomponentsinagoodworkingcondition[12,13].Duringthefrettingprocess,thehardnessmayvarythroughworkhardeningorsoftening,anidentifiedmechanisminfrettingfatigue[13].Thecompositionoftheatmosphere,relativehumidity,ambientpressureandtemperaturearetheenvironmentconditionswiththegreatestinfluenceonfretting.Thecompositionoftheatmo-spherecandictatethechemicalreactionsinthecontactzoneandthereforechangethefrettingresponse[14,15]aswellastherelativehumidity,whichcandirectlyinfluencethecoefficientoffrictionandtransformationsoftheweardebrisinthecontact[11,16–21].Theambientpressure(vacuum,ambientandhighpressure)[7,22,23]andthetemperature[15,24,25]areparameterswhosevariationhasadirectcorrelationwiththeoxidationofwearparticlesandcontactfilmsandconsequentlythewearvolume.Somestudiesregardingtheinfluenceofthesekindsofparameterscanbefound,specificallyonmechanicalworkalloysandsomecomposites,butwithlittleemphasisontheausteniticstainlesssteels.Oxidationphenomenaarecharacterizedbytheformationofoxidelayersinthecontact,dependingontheparametersmentionedabove,whichlargelydeterminesthebehaviorofthefrettingprocess[11,15,19,25].Theoxidesthatareexpectedtobefoundinasteelcontactshouldbeironoxides(Fe2O3andFe3O4)[15],althoughtheformationofthesecompoundsishighlyrelatedwithalloyelementsand/orwithsurfacemodificationtechniques[11,15,19].Also,thereisadistinctionbetweenoxidesthatareeitherbeneficial(protectivefilms)orharmful(damagingdebris)[11].Thefrettingfailuremechanism,understoodasthedisplace-mentvariationinmultiplebodiesincontactduringtime[6,16,26,27],canalsobeenhancedifthestressesonthebodiesincontactinducedbythemovementsvarysignificantlyduringtime,surpassingthematerialproperties[7,12,27–29].Averygoodtoolforwearestimationisthewearmap,specificallyinthisproject,duringtheworklifemaintenanceorfailingphases.Frettingmapscanbedividedintotwogroups:mapsunderfrettingwearconditionsandmapsunderfrettingfatigueconditions[27],dependingsolelyonthetypeoffrettingfailuremechanismonwhichitisbased.Therearecharacteristicallythreeregionsidentifiedinthefrettingprocess:theinitialstage(directcontactwiththesurfacesorthesurfacefilms),initiationofdebrisformation(beginningofthewearprocess)andthesteadystate(accommodationorexpellingofdebris)[30].Thedevelopmentoffrettingbehaviorisproposedbytwokindsofmodel:theArchardmodelandtheenergeticapproach.TheArchardmodelissuitableforlowvariationofthefrictioncoeffi-cientandadirectrelationbetweenappliedloadandwearvolume[31].Theenergeticapproachissuitableforanalyzinganenergeticparameterwhichvariesalongtheworkduration,forinstance,friction-dissipatedenergy[9,32–36].Theusualpalliatives/solutionsinfrettingaimtoattenuatetheextremeconditionineverysystem,sothatthelifetimeofthecouplingismaximized.Someofthosetechniquesaresurfacemodification(surfacetreatmentsandcoatings),directfrictionmodifiers(liquidorsolidlubricants),geometrymodificationandmaterialadaptation[8,23,29,32,36,37].Nowadays,stainlesssteelsarewidelyappliedintheelectricandelectronicindustriesmainlyforthecombinationoftheirlowcostandgoodmechanical,oxidationandelectricproperties.Afewstudiesfocusdirectlyonthisspecificapplication,althoughtheanalysisisnotusuallymultiparametricordoesnotfocusonthefrettingphenomena,solimitingtheapplicationoftheirresults[6,7,9,15,22].Someauthors[23,38]havestudiedthebehaviorofstainlesssteelswhensurfacemodificationtreatmentsareapplied.Thepresentstudyaimstoestablisharelationbetweendis-placement,relativehumidity,thenatureoftheatmosphereandtheinfluenceofmaterialpropertiesthroughtheenergeticapproach,regardingthedissipatedfrictionenergy,andtogenerateadimensionlessmodelfortheprojectandtheexpansionofthelifecycleofAISI304,anausteniticstainlesssteel.