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eeringimage/AnirbanMahatoResearchershavediscoveredapreviouslyunknownmechanismforwearinmetals:aswirling,fluid-likemicroscopicbehaviorinasolidpieceofmetalslidingoveranother.
Thefindingscouldbeusedtoimprovethedurabilityofmetalpartsinnumerousapplications.
"Wearisamajorcauseoffailureinengineeringapplications,"saidSrinivasanChandrasekar,aPurdueUniv.professorofindustrialengineeringandmaterialsengineering."However,ourfindingshaveimplicationsbeyondwearitself,extendingtomanufacturingandmaterialsprocessing."
ThefindingsaretheresultofacollaborationofresearchersfromPurdue,theIndianInstituteofScienceinBangalore,India,andM4Sciences,apanyinWestLafayette,Ind.
"Usinghigh-resolutionimagingofslidingcontactsinmetals,wehavedemonstratedanewwaybywhichwearparticlesandsurfacedefectscanform,"saidPurduepostdoctoralresearchassociateAnirbanMahato,whoisworkingwithChandrasekar,NarayanSundaram,anassistantprofessorattheIndianInstituteofScience,andYangGuo,aresearchscientistatM4Sciences.
FindingsaredetailedinaresearchpaperappearinginProceedingsoftheRoyalSociety.
Theresearchers,usingamicroscope,high-speedcameraandothertools,hadpreviouslyrevealedtheformationofbumps,foldsandvortex-likefeaturesonslidingmetalsurfaces.Thenewfindingsbuildonthepreviouspaper,publishedin2016inPhysicalReviewLetters,toshowhowthebehaviorleadstocracksandwearparticles.
Thefindingswerecounter-intuitivebecausetheexperimentwasconductedatroomtemperature,andtheslidingconditionsdidnotgenerateenoughheattosoftenthemetal.Yet,theswirlingflowismorelikebehaviorseeninfluidsthaninsolids,Chandrasekarsaid.
Theteamobservedwhathappenswhenawedge-shapedpieceofsteelslidesoveraflatpieceofaluminumorcopper.Themetalsaremonlyusedtomodelthemechanicalbehaviorofmetals.
"Wespeculatedintheearlierpaperthattheswirlyfluid-likesurfaceflowdiscoveredonslidingmetalsurfacesislikelytoimpactwearinslidingmetalsystems,"hesaid."Nowweareconfirmingthisspeculationbydirectobservations."
Theobservationsshowhowtinybumpsforminfrontofthewedge,followedbytheswirlingmovement.Whenthewedgeangleisshallow,theflowislaminar,orsmooth.However,itchangestoaswirlyflowwhentheangleisadjustedtoaless-shallowangle,mimickingwhathappensinactualslidingmetalparts.Asthewedgeslidesacrossthemetalspecimen,foldsformbetweenthebumps,andthenthefoldstransformintotearsandcracksinthewakeofthewedge,eventuallyfallingoffaswearparticles.
"Asingleslidingpassissufficienttodamagethesurface,andsubsequentpassesresultinthegenerationofplatelet-likewearparticles,"Chandrasekarsaid.
Thebehaviorwascapturedinmoviesthatshowtheflowincolor-codedlayersjustbelowthesurfacesofthecopperandaluminumspecimens.
Thedefectsrangeinsizefrom5to25micronsandaresimilartothosefoundinslidingponentssuchaspartsinautomotiveengines,pressorsandnumeroustypesofequipmentandmachinery.
"Inthepastweonlysawthesefeaturesaftertheyhadformed,andweattributedthemtovariouspossiblemechanisms,"hesaid."Here,weshowamechanismforhowtheyareformed.Thedefectfeaturesobservedalsooccurinsurfacescreatedbymanufacturingprocesseslikegrinding,polishing,burnishing,peening,drawing,extrusion,rolling,andsoon,whichareallmonlyusedinmakingstructuralandmechanicalponentsinthegroundtransportation,aerospace,sheet-andwire-metalsprocessing,andenergysystemssectors."
Ongoingresearchwillexplorepotentialroutestoreduceweararisingfromthistypeofmechanism.Metalsaremadeofgroupsofcrystalscalledgrains.Futureworkwillstudyhowamaterial'sgrainsizeandductilityinfluencethistypeofwear,howthesetypesofsurfacedefectsinmanufacturingprocessescanbeeliminatedthroughthemodifieddesignoftoolsanddies,improvedmodelsforslidingwearandwear-controlstrategies.
"Wewanttolookatthismechanisminmaterialsthathavesmallercrystals—inthe5to30micronrange,"Chandrasekarsaid."Wewanttoshowthatthemechanismismoregeneralandextendsdowntoevenfiner-grainedmetals."
Source:PurdueUniv.
金属在滑动部位磨损的关键发现
图像的序列揭示了在一个固体金属片没过另一个固体金属处时出现的令人惊讶的流体状行为,这形成了最终导致金属零件磨损的缺陷.(上)显示出这些缺陷是如何在接触之后出现的两个材料流动的图像帧.(下)呈现出撕裂和裂缝的相应磨损表面的扫描电镜照片.磨损颗粒是在撕裂和裂纹从表面分离时形成的.图片:普渡大学工业工程学院图像/艾米班马哈头
研究人员已经为金属的磨损发现了一种以前未知的机制:在一个固体金属片滑过另一个固体金属片时其内部存在的一个漩涡流体状的微观行为.
该研究结果可以被用来提高在众多应用中的金属部件的耐久性.
"磨损是工程应用失败的一个主要原因,"普渡大学工业工程和材料工程学教授斯里尼瓦桑钱德拉塞卡尔表示."然而,我们的研究结果具有超越磨损本身的影响,延伸到了制造和材料的加工."
这一发现是普渡大学的研究人员与印度班加罗尔的印度科学研究所以及印第安纳州拉斐特西部的M4科学公司一同协作的结果.
"使用金属中滑动触点的高分辨率成像,我们已经展示了一种新的方式,磨损颗粒和表面缺陷能够通过这种方式形成,"与钱德拉塞卡尔一同工作的普渡大学博士后研究助理艾米班马哈头,印度科学研究所的助理教授纳拉扬孙达拉姆,以及M4科学公司的一名研究科学家郭扬表示.
研究论文中的详细结果发表于《英国皇家学会论文集》.
使用显微镜,高速摄像机等工具的研究人员在此前曾透露出滑动金属
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