Characterization of nanostructured TiN coatings fa

CharacterizationofnanostructuredTiNcoatingsfabricatedbyreactiveplasmasprayingDongliZou⁎,DianranYan,LisongXiao,YanchunDongSchoolofMaterialsScienceandEngineering,HebeiUniversityofTechnology,Tianjin300132,ChinaReceived16May2007;acceptedinrevisedform16August2007Availableonline24August2007AbstractThenanostructuredTiNcoatingsarefabricatedbymeansofreactiveplasmasprayingmicrometerstitaniumpowdersintheatmosphere,andthemicrostructureandperformanceofthecoatingsareanalyzedbyXRD,SEMandTEM.TheexperimentalresultsshowthatthecoatingsaremainlycomposedofTiNandTi3Ophases,andthecoatingshavethetypicalsprayedlamellaestructures.Inparalleltosubstratesurfacedirection,thenanoscalegrainswithparticlediametersrangingfrom60to120nmareobservedinthecoatings,andbothfineequiaxedandcolumnargrainsarefoundinsomezonesofthenanostructuredTiNcoatings.Butinverticaltosubstratesurfacedirection,thecontraryisthecase.ThusitcanbeconcludedthattheTiNcoatingsarecomposedofthecolumnargrains,andthecolumnargrainsarenanostructuralequiaxedgrainsintheircross-section.Inaddition,alargenumberofdeformationtwinscausedbythestressesconcentrationarefoundinTiNcoatings.Meanwhile,thenanostructuredTiNcoatingshaveahigherbondingstrengthandbetterfracturetoughnessthanotherobservedas-sprayedcoatings.©2007ElsevierB.V.Allrightsreserved.Keywords:Reactiveplasmaspraying;TiNcoatings;Nanostructuredcoatings1.IntroductionTitaniumnitride(TiN)hasgoodcorrosionresistance,heatresistance,andwearresistanceproperty[1–3].Manyresearchershavestudiedtheformationprocess,microstructureandphysicalpropertiesofreactiveplasmasprayingTiNcoatings[4–7].ButthepropertiesofTiNcoatingsdeviateobviouslyfromthebulkTiNmaterialsduetothefactsthatthemicrostructureofcoatingsisrathersensitivetothecoatingprocessparameters.Therefore,acontinuousattemptisstillmadetoimprovethemicrostructureandpropertiesofTiNcoatingsdepositedusingvariousprocessparameters[8].Inaddition,depositionefficiencyofthecoatingsisveryimportanttolowerthecoatingcost.VeryhardtitaniumnitridecoatingscanbedepositedbyPVDandCVDtechniquebuttheireffectivenessislimitedbytheirlowthicknessandtheirlowdepositionefficiency[2].Reactiveplasmasprayingtechniquecanpositivelybeemployedtoincreasethecoatingshardness,toobtainthethicktitaniumnitridecompositecoatingsandtoimprovethewearperformances.Inthepresentwork,thenanostructuredTiNcoatingsarefabricatedbyreactiveplasmasprayingtitaniumpowderintheatmosphericconditions,andthedensitiesofthecoatingsimprove.Furthermore,themicrostructureofthereactiveplasmasprayingTiNcoatingsisanalyzedbyTEM,andthegrainsizeanddeformationtwinsincoatingsarestudied.2.Experimental2.1.FabricationoftheTiNcoatingsTheexperimentsarecarriedoutbyaplasmasprayingsystem,whichconsistedofaGP-80electricpowerof80KWandaBT-G3gunmanufacturedbyTaixingYeyuanDeviceCompanyinChina.Thepuretitaniumpowderusedinthepresentworkiscom-merciallyavailableandproducedbyBeijingGeneralResearchInstituteofMiningandMetallurgy,China.Theaverageparticlesizedistributionofthetitaniumpowderisabout30–40μm.TheAvailableonlineatwww.sciencedirect.comSurface&CoatingsTechnology202(2008)1928–1934www.elsevier.com/locate/surfcoat⁎Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](D.Zou).0257-8972/$-seefrontmatter©2007ElsevierB.V.Allrightsreserved.doi:10.1016/j.surfcoat.2007.08.022substratematerialusedisQ235(Fe,and1.4–2.2wt.%C)steel,whichismachinedintosamplesof10mm×12mm×10mm,andgroundtoroughsurfacesusingquartzsand(120mesh).PriortoreactiveplasmasprayingTiNcompositecoatings,Ni–10wt.%Alself-meltingalloybondlayerwithathicknessofabout100μmissprayedontosurfacesofsamples.ThegraindistributionofNi–10wt.%Alpowdersisrangingfrom20μmto50μmandthesprayingparametersareshowninTable1.Duringtheprocedure,titaniumpowderswerecarriedbynitrogengasintotheArandN2containingplasmajet,wherechemicalreactionoccurredbetweenpurenitrogengasandtitaniumpowders.Thus,aTiNcompositecoatingwithathick-nessofover300μmwasproducedwithinafewminutes.ThecompositionsofsprayingtitaniumpowderareshowninTable2andthesprayingparametersareshowninTable3.2.2.CharacterizationXRDcharacterizationwasperformedonthesurfaceofthecoatingsbymeansoftheJEOLRigakuX-rayDiffractometer2500/PCdiffractioninstrumentwithaCuKaradiation(100–900).Allspecimensaregroundandpolished,thenthespecimenswereobservedbyaPHILIPSXL33-TMPscanningelectronmicroscope.SelectedspecimenswerescrapedfromsubstrateforTEM,followedbymechanicalpolishingtoathicknessof70μm.Finallythestandard3mmdiscswerepunched,thenthinnedtoelectrontransparencywasachievedbyelectronthinningforobservation.TransmissionelectronmicroscopywascarriedoutinPHILIPSTECNAI-20at200kV.ThebondingstrengthtestoftheTiNcoatingswasmeasuredbythetensiletestsample.ThedetailprocedureisthatthesamplesurfacewassprayedTiNcoatingswithabout0.5mmthickness,thenadhibitedanothersampleuptothecoatingssampleusingadhesiveemulsion.Whentensiletestexperimentwithtensiletestspeedabout9807N/minwasproceeding,theloadwastrackrecordeduntilsamplerupture,thenthebondingstrengthoftheRPSTiNcoatingwasobtainedbyequation.Micro-indentationofthecross-sectional