机械毕业设计英文外文翻译金刚石刀具机械研磨过程中材料的去除机理.docx

机械毕业设计英文外文翻译金刚石刀具机械研磨过程中材料的去除机理.docx

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机械毕业设计英文外文翻译金刚石刀具机械研磨过程中材料的去除机理

附录

外文翻译：

MaterialRemovingMechanismforMechanical

LappingofDiamondCuttingTools

LIZeng-qiang，ZONGWen-jun，SUNTao，DONGShen

（CenterforPrecisionEngineering，HarbinInstituteofTechnology，Harbin150001，China）

Abstract：

Thematerialremovingmechanismformechanicallappingofdiamondcuttingtoolswasilluminatedattheatomisticscale.Inlappingprocess，phasetransformationofthelappingregionwasthemainreasonforthematerialremoval.Thusathree-dimensionalmodelofaspecimenofthediamondmonocrystalandrigiddiamondgritwasbuiltwiththeaidofthemoleculardynamics（MD）simulation.TheforcebetweenalloftheatomswascalculatedbytheTersoffpotential.After

that，lappingwithacertaincuttingdepthof1.5latticeconstantswassimulated.Bymonitoringthepositionsofatomswithinthemodel，themicrostructureinthelappingregionchangesasdiamondtransformedfromitsdiamondcubicstructuretoamorphouscarbonwereidentified.Thechangeofstructurewasaccomplishedbytheflatteningofthetetrahedronstructureindiamond.Thiswasverifiedbycomparingtheradialdistributionfunctionsofatomsinthelappingandun-lappingregions.Meanwhile，thedebrisproducedinlappingexperimentwasanalyzedbyXRD（X-raydiffraction）.Theresultsshowthatthephasetransformationhappensindeed.

Keywords：

diamondcuttingtools；mechanicallapping；materialremovingmechanism；moleculardynamicssimulation

Itisanimportantwaytoturntheopticalsurfacewithnaturaldiamondcuttingtoolstoobtainhighaccuracy.Theprocessedwork-pieces’surfacehaslowersurfaceroughnessandresidualstress，andsmallermetamorphicregionthanthosemachinedinusualways.

Diamondisthemostimportantmaterialtomakecuttingtoolsintheultra-precisionmachining，foritisanidealbrittlesolidwiththegreatesthardnessandresistancetoplasticdeformationofanymaterialandhasveryhighdimensionalhomogeneity.Thesharpeningmethodofdiamondcuttingtoolsisthekeytechnologytoobtainsharpcuttingradius，goodsurfacequalityandsmallgeometrictolerance[1].Therearemanysharpeningmethodssuchaslapping，ionbeamsputtering，thermalchemistrypolishing，plasmapolishing，oxideetchingandlasererosion，etc.Themostcommonandeffectivemethodislapping[2].Themechanismofthematerialremovalinlappinghasalotofstatementssuchasthemicro-cleavagetheory[3]，thethermalabrasiontheory[4]，electro-abrasiontheory[5]andtheoryoffracturetakingplaceintheharddirection[6]，etc.However，theseexplanationsareonlysatisfactoryintheparticularsituation.Theexplanationacceptedbymostpeopleisthatthehybridizedorbitofthecarbonconvertsfromsp3tosp2inlapping，asdemonstratedbyvanBouwelen[7]，Grillo[8]，HirdandField[9].Asyet，fewmanhasverifieditattheatomisticlevel.

Theextremelypowerfultechniqueofmoleculardynamics（MD）simulationinvolvessolvingtheclassicalmany-bodyproblemincontextsrelatingtothestudyofmatterattheatomisticlevel.Sincethereisnoalternativeapproachcapableofhandlingthisbroadrangeofproblemsattherequiredlevelofdetail，moleculardynamicsmethodshavebeenprovedindispensableinbothpureandappliedresearch，asdemonstratedbyRapaport[10].Moleculardynamicsanalysisisaneffectivemethodinstudyingindentation，adhesion，wearandfriction，surfacedefectsandnano-cuttingattheatomisticscale.Nowadays，MDanalysishasalreadybeenemployedtoinvestigatetheAFM-basednanolithographyprocessusinganAFMtool[11]andatomicsurfacemodificationinmonocrystallinesilicon[12].Therefore，itisanefficientwaytoapproachthemechanismofthematerialremovalinlappingusingmoleculardynamicssimulation.

Fromalltheabove，thisstudywillfocusonthematerialremovingmechanismindiamondmechanicallappingusingthree-dimensionalMDsimulation.Andthemicrocosmicphenomenainmechanicallappingwillbepresentedanddiscussed.

1Methods

1.1Simulationmodeling

Atthebeginning，themechanicallappingprocessofdiamondcuttingtoolsisintroduced.Thescaifeusedwasmadefromagreycastironandwasmedium“striped”（radialgroovestoholddiamondgrit）.Itwas

preparedforusebyapplyingafilmofoliveoiltothesurface，beforeafewcaratsofgradeddiamondgritswererubbedevenlyintoit.Withthescaiferunningatahighspeed，adiamondcuttingtoolwaslappedbyapplyingaload.Inthisprocess，thediamondgritwasfixedinthescaife.So，theprocessbelongstothefixedabrasivepolishingcategory[13].Therefore，amodelofaspecimenofthediamondmonocrystalandrigiddiamondgritwasbuilt，asshowninFig.1.

Fig.1Moleculardynamicssimulationmodelofmechanicallappingofdiamondcuttingtools

Thecrystallatticeofthespecimenandthegritbelongedtothediamondcubicsystem.Thelatticeconstantofthissystemwas0.35667nm，whichwasrepresentedasa.Thecontrolvolumeofthespecimenmustbelargeenoughtoeliminateboundaryeffects.Takingthisintoconsideration，anoptimumcontrolvolumewaschosenbasedonaniterativeprocessofincreasingthecontrolvolumesizeuntilfurtherincreasesdidnotaffectthedisplacementsandvelocitiesoftheatomsduetolapping.Anoptimumsizeof50a×15a×30awasobtained，consistingof183,930atoms.Moreover，theperiodicboundaryconditionwasusedinthez-directiontoreducetheeffectsofthesimulationscale.Thespecimenincludedthreekindsofatoms，namely：

boundaryatoms，thermostatatomsandNewtonianatoms.Torestricttherigid-bodymotionofthespecimen，theboundaryatomsintheleftandbottomlayersofthespecimenthatwerefixedinspacewereusedtocontaintheNewtonianatoms.Thermostatatomswerealsousedtoensurereasonableoutwardheatconductionawayfromthecontrolvolume.ThermostatatomsandtheNewtonianatomsobeytheNewton’ssecondlaw.Thetopsurfaceofthespecimenwas（100）surface，whichwasexposedtothegrit.Thesphericaldiamondgrithadaradiusof8a，consistingof17,116atoms.Anditslidonthespecimenwiththedepthofh.

Beforecarryingoutthemoleculardynamicssimulationonthelappingofdiamond，itisimportanttoensurethatthechosenpotentialfunctiongivesareliableresultforthesimulation.Tersoffpotentialwasusedinthepresentsimulationtodictatetheinteractionamongthediamondatomsinthissimulation[14].TheparametersinTersoffpotentialforcarbonwereasfollows：

A=1,393.6eV，B=347.6eV，λ=34.879nm.1，μ=22.119nm.1，β=1.572,4×10.7，n=0.727,51，c=380,49，d=4.384，h=.0.57058，R=0.18nm，andS=0.21nm.PositionsandvelocitiesoftheatomsweredeterminedbytheVerletmethodasdemonstratedbyMaekawaandItoh[15].Tosimulatelappingunderroom-temperatureconditions，thediamondatomswerearrangedinaperfectdiamondcubicstructurewiththelatticeparametersequaltotheirequilibriumvaluesatanambienttemperatureof293K.Theambienttemperaturewasmaintainedbyscalingthevelocitiesofthethermostatatomsateveryspecialtimestep.Inthissimulation，the0.5fswasselectedasthetimesteptoobtainahighaccuracy.

ThissimulationwascalculatedbytheLammpssoftware[16]，andvisualizedbytheVMDsoftware[17].Thevelocityofthelappingwas100awith1.5aincuttingdepthand40ainlappinglength.Beforethesimulation，thespecimenhadbeenrelaxedfor10000timestepsinordertomaintainthethermalbalance.

1.2Experiment

ThetestapparatusoflappingexperimentisshowninFig.2.Theabrasiveusedwasdiamondgritwithanaverageradiusof0.1μm.Theywerecoatedonthescaifeinaringwitharadiusof120mm.Thediamondcuttingtoolwasfixedonthearmbyaspecialfixture.Then，the

toolwaslappedwiththescaiferunningat3000r/min（ca.38m/s），underaloadof5Nwhichwasobtainedbyadjustingtheplaceoftheweight.Thedebriswascollectedafter30minlapping.Thereafter，theXRDstudieswerecarriedoutbySHIMADZUXRD-6000.

Fig.2Schematicdiagramofthelappingapparatus

2Resultsanddiscussions

2.1Moleculardynamicsanalysis

The3Dviewandcross-sectionviewofthesimulationareshowninFig.3.Thecrystallatticesnearthediamondgritaredistortedwhenthediamondgritcutsintothespecimen.Theregionincludingthesecrystallatticesishalf-ellipseinshape.Theregionisunderthediamondgritandabitlefttothecentero.Andthemajoraxisoftheellipseisinthesamedirectionasthecompositionofforces.Furthermore，thisregionmovesleftasthediamondgritslides.

AsshowninFig.4，A1+A2

Fig.3Microstructureofspecimenafterthegritsliding

Fig.4Sectionofthegroovesinthelongitudinaldirection

Therearethreekeypointsinlapping，asshowninFig.5.Firstly，atomsnearthediamondgritareforcedtomakesomedisplacementfromtheirinitialposition.Thecrystallatticesincludingtheseatomsdistortalittle.Theboundarybetweenthedistortedlatticesandtheperfectlatticesisalongthediamond（111）surface（theblacklines）asshowninFig.5（a）.Thedisplacementsoftheatomsbecomebiggerandbiggeralongwiththediamondgritslidingleft.Moreandmoreatomsdeviatefromtheirinitialposition.Thelatticesincludingtheseatomsdistortseriously.Thephasetransformationthatthediamondcubicdiamondtransformsintoamorphousgraphitestartsonafewatoms（inthedarkcircles）attheendofthismoment.Thatistosaythatthehybridizedorbitconvertsfromsp3tosp2.Secondly，thelatticesbelowthediamondgrithave