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Vacuum73(2004)643–648
Amechanicalaspectofboridesformedonthe
AISI440Cstainless-steel
IbrahimOzbeka,SadumanSena,MedihaIpeka,CumaBindala,
SakinZeytina,A.HikmetUcisikb,*
aDepartmentofMetallurgyandMaterialsEngineering,EngineeringFaculty,SakaryaUniversity,54187EsentepeCampus,Sakarya,TurkeybBogaziciUniversity,DepartmentofProstheses,MaterialsandArtificialOrgans,InstituteofBiomedicalEngineering,Bebek-Istanbul80815,Turkey
Abstract
Inthepresentstudy,somepropertiesofboridesformedonAISI440Cstainless-steelhavebeeninvestigated.BoronizingwascarriedoutinasolidmediumconsistingofEKaborspowderatatemperatureof950Cfor2–8h.Thepresenceofboridese.g.FeB,Fe2B,CrB,Cr2B,Mn2BandMnBwererevealedbymeansofX-raydiffractometry,scanningelectronmicroscopy,andopticalmicroscopy.Thehardnessofborideswhichwasover1500VHNandboridelayerthicknessweremeasuredanditwasobservedthat,thethicknessesoftheboridelayerswerestronglydependentontheprocesstime,andchemicalcompositionofthesubstratematerials.Itwasalsofoundthatthelongerboronizingtimeresultsinanincreaseinthicknesslayer;thethicknessofboridelayersrangedfrom10to50mm.OpticalmicroscopyexaminationsoftheboridesformedonthesurfaceofAISI440Cstainless-steelsubstraterevealedasmoothandcompactmorphology.TodeterminedistributionofalloyingelementsfromsurfacetotheinteriorenergydispersiveX-rayspectroscopywasused.r2004ElsevierLtd.Allrightsreserved.
Keywords:Boronizing;Stainless-steel;Microstructureofboridedzone;Indentation
1.Introduction
Boronizingisathermochemicaldiffusionsur-
facetreatmentinwhichboronatomsarediffused
intothesurfaceofworkpiecetoformhardborides
withthebasematerial[1–4]anditisaprominentchoiceforawiderangeoftribologicalapplications
wherethecontroloffrictionandwearisof
primaryconcern[5].Boronizingcanbeapplied
toawiderangeofsteelalloysincludingcarbon-
steel,lowalloy-steel,tool-steelandstainless-steel.
Inaddition,materialssuchasnickelbasedalloys,
cobaltbasedalloys,molybdenumandtitanium
canbeboronizedtoobtainveryhighhardnessand
wearresistantontheirsurfaces[6–11].Inparti-
cular,boronizingcanincreasetheresistanceof
lowalloysteeltoacidssuchassulfuric,phosphoric
andhydrochloricacids.Inaddition,boronized*Correspondingauthor.BogaziciUniversity,DepartmentofProstheses,MaterialsandArtificialOrgans,InstituteofBiomedicalEngineering,Bebek-Istanbul80815,Turkey.Fax:+90-212-227-79-34.E-mailaddress:hucisik@hotmail.com(A.HikmetUcisik).
0042-207X/$-seefrontmatterr2004ElsevierLtd.Allrightsreserved.doi:10.1016/j.vacuum.2003.12.083austeniticstainless-steelhasexcellentresistanceto
hydrochloricacid[2,12–14].Inthisstudy,we
investigatedsomepropertiesofboridesformed
onAS440Cstainless-steelwhichisextensively
usedforball-bearingsandraces,seats,pump
parts,surgicaltools,implantmaterialandcutlery.
AISI440Cstainless-steelshasalsohighcarbon
andchromiumcontentandtherefore,itmaybe
hardenedandtemperedtoincreasewearresis-
tance.
Atpresentstudy,weattempttoelucidatesome
propertiesofboronizedAISI440Cstainless-steel,
e.g.distributionofalloyingelements,microstruc-
tureofboridedzoneetc.Specifically,weuseda
Vickersindenterandanopticalmicroscopeto
determinehardnessandmicrostructuresofbor-
onizedAISI440Cstainless-steel.Todetermine
distributionofalloyingelementsfromthesurface
totheinteriorenergydispersiveX-rayspectro-
scopy(EDS)wasused.
2.Experimentaldetails
2.1.Substratematerials
Thesubstratematerialusedinthisstudywas
AS440Cstainless-steelwithchemicalcomposi-
tiongiveninTable1.ThetestpiecesofAISI440C
stainless-steelhadadimensionof15mmÂ
15mmÂ3mm.
2.2.Boronizing
Boronizingwascarriedoutinasolidmedium
consistingofEKabor2spowders(BorTec
GmbH).Testsamplestobeboronizedwereplaced
incontactwithEKabor2spowdersandthen
placedinelectricalresistancefurnace.Thetest
sampleswereheatedtoatemperatureof950C
underatmosphericpressureandholdforapredeterminedamountoftime(about2–8h).This
isfollowedbyquenchinginair.
2.3.Filmcharacterization
Thestructureandtypeofboridesformedon
AS440Cstainless-steeliscloselyrelatedtothe
chemicalcompositionofAISI440Cstainless-steel
substrateusedinthisstudy.Thepresenceof
boridesformedincoatinglayerwasconfirmedby
meansofX-raydiffractometry(XRD),andoptical
microscopy.APhillipshighresolutiondiffract-
ometerwasemployedforXRDanalysisofthe
boridesformedonAISI440Cstainless-steel
surfaces.ACoKaradiationwithawavelengthof
1.790(Awasusedovera2yrangeof20–90.
OlympusBHM-313opticalmicroscopewasalso
utilizedforexaminingmicrostructures.Thedis-
tributionofalloyingelementswasconfirmedvia
EDSfromsurfacetointerior.
2.4.Hardnessandthicknessofcoatinglayer
Themicrohardnessofborideswasmeasuredby
usingaVickersmicrohardnesstesterandaloadof
0.5N.Atleastfiveindentationsweremadeoneach
coatingfilmundereachexperimentalconditionto
checkreproducibilityofthehardnessdata.The
thicknessesofthecoatinglayerweremeasuredby