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Laseradditivesynthesisofhighentropyalloycoatingonaluminum:CorrosionbehaviorYoukangShona,SameehanS.Joshib,ShravanaKatakamb,RaviShankerRajamureb,NarendraB.Dahotreb,naTexasAcademyofMathsandScience,UniversityofNorthTexas,1155UnionCircle305309,Denton,TX76203-5017,USAbLaboratoryforLaserAidedAdditiveandSubtractiveManufacturing,DepartmentofMaterialsScienceandEngineering,UniversityofNorthTexas,1150UnionCircle305310,Denton,TX76203-5017,USAarticleinfoArticlehistory:Received22September2014Accepted29November2014Availableonline9December2014Keywords:LaserprocessingHighentropyalloysCoatingsabstractHighentropyalloycoatingsweresynthesizedonaluminumsubstratebylasersurfaceengineering.Dilutionfromthesubstratewasminimizedwiththeaidofmultilayeredcoatings.Furthermore,higherlaserinputenergyduringprocessingleadtouniformmixingamongstthecomponentsresultinginformationofevenlydistributedhighentropyalloyphasesthroughoutthematrix.ThisresultedinenhancedcorrosionresistanceforthecoatingsinnearneutralNaClsolution.&2014ElsevierB.V.Allrightsreserved.1.IntroductionHighentropyalloys(HEAs)areemergingclassofalloyswhicharebasedonthepresenceofmultiplecomponents,inequimolarornearequimolarratio.Multiplecomponents/elementsgiverisetoincreas-ingeffectsofconfigurationalentropyresultinginstabilizationofarandomizedsolidsolutionphase[1,2].HEAshavebeenreportedtopossesexcellentsetofbulkpropertiessuchasmechanicalstrengthandductility[3,4],softmagneticproperties[5].Theyalsohavesuperiorsurfacepropertieslikehighhardness[6,7],betterwearperformance[8,9]andsuperiorcorrosionresistance[7,10,11]mak-ingthemsuitablecandidateascoatingmaterial.Additionally,con-sideringthecomplexnatureofthesystem,itismorefeasibletouseHEAsascoatingsratherthanbulksoastotakeadvantageofthepropertiespossessedbythesesmaterials.ThefieldofHEAcoatingsisnewandsomeoftherecentstudieshavereportedsynthesisofHEAcoatingsbyvariousmethodslikemagnetronsputtering[12],electrosparkprocess[13],plasmaarccladding[14],andalsobylaserprocessing[15–18].Laserprocessingisparticularlyattractivemethodwhichprovidesquickheatingofthecoatingmaterialstohightemperaturesfollowedbytherapidquenching.ThermalentropycontributionsaddtotheconfigurationalentropyathightemperaturesmakingconditionssuitableforHEAformationandrapidquenchingensuresretentionoftheHEAphaseatroomtemperature[18,17].Yeetal.[15]synthesizedAlxFeCoNiCuCr(xvaryingfrom1to2)HEAalloyonaluminumbylasercladding.Thehightemperaturehardness,abrasionperformance,andcorro-sionresponseofthecoatingssynthesizedwithvaryingamountsofAlweretested.OptimumsetofpropertieswereobtainedforintermediateAlcontentof1.8byatomicratio.Zhangetal.[17]havereportedthesynthesisofFeNiCoSiCrAlTiHEAcoatingonQ235steelsubstrateusinglaserprocessing.ItwasobservedthatHEAcoatingformedforhigherconcentrationofFe(6FeNiCoSiCrAlTi).Theevolu-tionofasimpleBCCHEAphase/microstructurewasattributedtotherapidquenchingduringlaserprocessing.Therearemanycomposi-tionspossibleunderHEAcategoryandoneofthewellknownsystemsisAl–Fe–Cr–Co–Nisystem,possessingattractivesetofpropertiessuchasmechanicalproperties[4],highhardnessand[6,7]corrosionresistance[7,11]andgoodelevatedtemperatureproperties[19].Bettermicromechanicalpropertiesofthissystemhavebeenpredictedbytheoreticalcalculations[20].PreviousinvestigationfrompresentresearchgrouphasreportedsuccessfulsynthesisofAl–Fe–Cr–Co–Nibylasersurfaceengineering[18].DetailedinvestigationaboutmicrostructureevolutionwascarriedoutandinfluenceofprocessingandthermodynamicparametersonstabilityofHEAphasewereinvestigated.CurrentreportfocusesoncorrosionpropertiesoflasersynthesizedAl–Fe–Cr–Co–Nicoating.Effectofadditivelyproduceddoublelayeredcoatingsondilutionfromthesubstrateandsubsequentcorrosionresistanceisreported.2.MethodsandmaterialsTheHEAcoatingsweresynthesizedusinghighpowerYtter-biumdopedNd-YAG(YLS-3000IPG)continuouswavelaserwithContentslistsavailableatScienceDirectjournalhomepage:://dx.doi.org/10.1016/j.matlet.2014.11.1610167-577X/&2014ElsevierB.V.Allrightsreserved.nCorrespondingauthor.E-mailaddress:Narendra.Dahotre@unt.edu(N.B.Dahotre).MaterialsLetters142(2015)122–125awavelengthof1064nmandlaserbeamdiameterof0.6mm.Energyinputsof21Jmm2and25Jmm2wereobtainedwithcombinationofinputpowerof1000Wand1200Wwithfillspacing/lasertrackoverlapof0.4and0.3mmrespectively.Thebeamscanningspeedwaskeptconstantat100mm/s.Al,Fe,Co,Cr,andNielementalpowders(withaverageparticlesizesrangingfrom1to3μm)withapurityof99.99%inequiatomicratioweremixedwithawatersolubleorganicbinder(LISIW15853obtainedfromWarrenPaintandColorCompany,Nashville,TN,USA)toformathickslurry.Theslurrywasthenuniformlydeposited(averagethickness300μm)onto1100Alsubstrateusingair-spraytechnique.Thesubstrateswerethoroughlycleanedinacetoneanddriedpriortodepositionofthepowders.Thelaserparameterswereselectedbasedonpriorexperienceaftermanytrialsinordertoobtainauniformandsoundcoating.Althoughtheseparametersarenotthemostoptimum,primarypurposeofthispreliminarystudywastoproduceHEAcoatingsusinglaserprocessingandstudytheircorrosionbehavior