research article the tribological property and...

Research ArticleThe Tribological Property and Microstructure of Ni-Ti CoatingPrepared by Electrodeposition and Heat Treatment

Chufeng Sun12 Yanbin Wang1 Qiong Su1 Zhiguang Guo2 and Lei Shi2

1College of Chemical Engineering Northwest University for Nationalities Lanzhou 730030 China2State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of SciencesLanzhou 730000 China

Correspondence should be addressed to Lei Shi leishilicpcascn

Received 13 November 2015 Accepted 24 January 2016

Academic Editor Somchai Thongtem

Copyright copy 2016 Chufeng Sun et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Ni-Ti coatings were fabricated by the electrodeposition in a Ni plating bath containing Ti power and heat treatment in nitrogenatmosphere The surface morphology and microstructure of the Ni-Ti coating before and after heat treatment were analyzed bymeans of scanning electron microscopy and X-ray diffraction The friction and wear behaviors of two different coatings wereevaluated on a ball-on-disk UMT-2MT test rig It was found that the phase structure of Ni-Ti coating heated in nitrogen wasmuch different from that of the as-deposited Ni-Ti coating Namely the new intermetallic compounds including Ni

3Ti NiTi and

NiTi2 and TiN were detected in the coating after heat treatment by the XRD analysis and contributed to greatly increasing the

hardness and tribological property of the Ni-Ti coating owing to the strengthening effect of the hard intermetallic compounds andTiN phase At the same time a small amount of intermetallic compounds and TiN was transferred from the composite coating tothe rubbing surface of the counterpart steel ball during the sliding which also contributed to decreasing the friction coefficient andincreasing the wear resistance

1 Introduction

Ni-Ti alloys or coatings usually have various special prop-erties such as biocompatibility [1 2] shape memory effect[3 4] good wear resistance and corrosion resistance [5ndash7] This is why Ni-Ti alloys or coatings have been findingincreased application in the fields of biomedical technologyelectronic industries aerospace automobile and so forthNi-Ti alloys or composites have been fabricated by varioustechniques and methods such as spraying [8 9] magnetronsputtering [10 11] and powder metallurgy [12ndash14] Amongthose methods electrodeposition is of particular significanceas a technique for producing various composite coatingsat a normal pressure ambient temperature low cost andhigh deposition rate Such a significance of electrodepositioncould not be underestimated since it is feasible to preparemetal-particulates doped metal-matrix composite coatingssuch as Ni-Ti Ni-Al and Ni-Cr making use of the in situcodeposition of themetallic particles in the electrodeposition

process [15ndash17] By means of heat treatment of the as-deposited metal-matrixmetal particle composite coatingsome new compounds are formed which needless to sayusually would be difficult or impossible to produce usingconventional electrodeposition methods

Ni-Ti coating prepared by the electrodeposition in anickel plating bath containing Ti powers has been reportedby Budniokrsquos group [15 16] Hasannaeimi et al [18] andZhao et al [19] and so forth The intermetallic compoundscan be formed in Ni-matrix composites via heat treatmentof electrodeposited Ni-Ti coatings With a view to thecorrelation among the structures and performances of thecomposite materials it could be practicable by heat treatmentto endow Ni-Ti composite coating with special propertiesdifferent from properties of the electrodeposited Ni-Ti coat-ing because some intermetalic compounds possess highmicrohardness and good antifriction and wear resistanceUnfortunately most of the reports about electrodepositedNi-Ti coating are focusing on the effect of the preparation

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2016 Article ID 8750657 6 pageshttpdxdoiorg10115520168750657

2 Advances in Materials Science and Engineering

parameter for examplemetal powder amount in the bath anddeposition current density on the chemical composition [18]and structure and corrosion properties of the coatings [19]and so far little work has been reported on the tribologicalproperties of Ni-Ti coatings via electrodeposition and heattreatment The as-deposited Ni-Ti coating was heat-treatedin pure N

2atmosphere which was aiming at increasing the

mechanical strength of the coating by the generation of Ni-Ti intermetallic compounds and TiN with good chemicalstability high microhardness and good wear resistance Thesurface morphologies structures and hardness and tribolog-ical properties of Ni-Ti coatings before and after the thermaltreatment were comparatively investigated

2 Materials and Methods

The plating bath is composed of 200 gsdotLminus1 NiSO4 35 gsdotLminus1

NiCl2 30 gsdotLminus1 Na

3C6H5O7 30 gsdotLminus1 H

3BO3 and 2 gsdotLminus1 Ti

powders Analytical reagents and distilled water were usedto prepare the electrodeposition solution The pH value ofthe solution is about 38 plusmn 01 and the electrodeposition timewas 30min The Ti powders (diameter of grains sim20120583mpurity 999) were dispersed in the electrolyte before platingThe electrodeposition was performed on a model 273Apotentiostatgalvanostat device (EGampG Princeton AppliedResearch) at 45∘C and a current density of 50mAsdotcmminus2

During the electrodeposition process the bathwas stirredby a magnetic stirrer at a stirring rate of 150 rpm to ensurea homogeneous suspension and facilitate transportation ofthe Ti suspension towards the substrate A platinum meshof 40 times 40mm2 was used as the anode and a saturatedcalomel electrode (SCE) was used as the reference electrodeA 1Cr18Ni9Ti steel plate of a size 10mm times 10mm times 1mm anda surface roughness less than 005 120583m were used as the cath-ode substrate The steel plate was sequentially ultrasonicallycleaned in ethanol acetone and distilled water for 10minactivated in a mixture of HCl and H

2SO4for 30 s washed in

distilledwater and then immersed immediately in the platingbath to deposit Ni-Ti coating

The as-deposited Ni-Ti coating with the thickness ofabout 110 plusmn 10 120583m was heated at 850∘C for 20 h in purenitrogen atmosphere using a muffle furnace with the heatingrate of 5∘Cmin The morphologies of the coatings wereobserved using a scanning electron microscope (JEOL JSM-5600LV) The phase structures of the coatings were ana-lyzed using an X-ray diffractometer (XRD Philips X1015840 Pert-MRD) The hardness of the coatings was measured on aVickersrsquo microhardness instrument at a load of 50 g for 5 sFive measurements were processed on each sample and theresults were averaged Since the measurement of hardness isalways influenced by the substrate the Jonsson andHogmarkmethod [20] was used to dissociate the contributions of thesubstrate and coating of measured hardnessThe deviation ofthe average hardness is less than 4The tribological proper-ties of the coatings reciprocally sliding against SAE52100 steelball (3mm) were tested on a UMT-2MT test rig (see Figure 1)in a ball-on-disk configuration The amplitude of the slidingwas 5mm a normal load was 05sim40N and a frequencywas 30Hz All the tribological tests were performed under

Counterface ball

Specimen holder

Dead load

Specimen

Ball holder

Figure 1 Diagrammatic sketch of the friction couple contact

dry friction condition at room temperature and in ambientair The friction coefficient was automatically continuouslyrecorded during the test

3 Results and Discussion

31 Structures and Morphological Characterizations of Ni-Ti Coatings Figure 2 shows the XRD patterns of the as-deposited Ni-Ti coatings before and after heat treatment Itis seen that the as-deposited Ni-Ti coating is characterizedby two-phase structure that is the nickel and titanium(Figure 2(a)) Namely the XRDpattern of these coatings con-firmed presence of themetal particles embedded into a nickelcrystalline matrix This also confirms that crystalline solidparticles of Ti could be embedded into the Ni matrix duringthe electrodepositionThe Ti phase has a hexagonal structureand the Ni has a cubic structure After heat treatment in N

2

atmosphere the coatings consist of Ni3Ti phase with some

minor phases of NiTi TiN andNiTi2and a sporadic phase of

Ni (Figure 2(b)) N2gas reacts with Ti particles on the coating

surface and simultaneously permeate through pores to reactwith Ti particles inside the coating to product TiN phaseunder N

2atmosphere and high temperature In other words

Ni and Ti in the as-deposited coatings almost transforminto Ni-Ti intermetallic compounds and TiN during the heattreatment process

The electrodepositionmechanism of Ni-Ti coating can beexplained by the adsorption of Ni ions on the Ti particlessurface Ni2+ ions which partly lack the hydration wrappingcan be electrochemically active and liable to move towardsthe cathode Because of the electrical conductivity of metal Tiparticles Ni experiences transition reaction and is depositedboth on the surface of the subtrate and on Ti particles whichallows the generation of the composite coating structure [1618 21]

Figure 3 shows the SEM morphologies of the Ni-Ticoating before and after the heat treatment It is seen that as-deposited Ni-Ti coating has a particulate-like structure andgranular morphology (Figure 3(a)) which indicates that thecodeposited Ti particulates were uniformly distributed in theNi matrix of the coating It was also found that the presenceof metal particles embedded into the nickel matrix distinctlyenlarge the real surface of the coatings This is because thegrowth becomes more 3D in character leading to dendrites

Advances in Materials Science and Engineering 3

20 30 40 50 60 70 80 90

5000

10000

15000

20000

25000

30000

Ο

NiΟ Ti

Ο

Inte

nsity

(cps

)

2120579 (deg)

nabla

nabla

nabla

nabla

(a)

30 40 50 60 70 80 90

5000

10000

15000

20000

25000

30000

35000

bullloz

lozbullbull

Inte

nsity

(cps

)

bull NiTiloz

TiNNi

loz

bull

2120579 (deg)

Ni3Ti

NiTi2

nablanabla

nabla

Δ

Δ

Δ ⧫

⧫

⧫

⧫

(b)

Figure 2 XRD patterns of Ni-Ti coatings (a) before and (b) after the heat treatment

(a) (b)

Figure 3 SEMmicrographs of Ni-Ti coatings before heat treatment (a) and after heat treatment (b) under the same magnification (zoom intimes500)

embedded into the layer It could be observed that Ni + Ticoatings morphology clearly changes after heat treatment for20 h (Figure 3) Namely the heat treatment influenced thesurface development of the layers obtained This is a resultof total chemical reaction between Ni Ti and N

2which leads

to a homogenization of the surfaceThe surface of Ni-Ti com-posite coating after the heat treatment hasmuchmore flat andfiner particles in appearance than that of as-deposited coating(Figure 3(b)) It could be rational to suppose that Newlygenerated Ni-Ti intermetallic compounds could uniformlydistribute in the coatings Because N

2cannot completely

diffuse into the entire coating the content of TiN near theouter surface is predicted to be higher than that of TiN insidethe coating The hard intermetallic compounds and a smallamount of TiN may contribute to increasing the mechanicaland tribological properties of the composite coatings

32 Tribological Properties of Ni-Ti Coatings The productionof the intermetallic compounds and a small amount of TiNphases led to a significant increase in the surface microhard-ness of the composite coating Namely the microhardness ofthe coating after the heat treatment is as high as about 395Hvand that of the coating before the heat treatment is 198HvThis means the heat treatment nearly doubles the hardness ofthe Ni-Ti coatingThis is connected with the special structureof the composite coating containing a great amount of hardintermetallic compounds including Ni

3Ti NiTi and NiTi

2

and a small amount of TiNFigure 4 shows the variation in the friction coefficients

of the Ni-Ti coating after the heat treatment with the slidingcycles under the different load It is seen that the frictioncoefficients of the composite coating gradually increase withincreasing sliding cycles except that the friction coefficient


0 400 800 1200 1600 200000

01

02

03

04

05

06

Fric

tion

coeffi

cien

t

Sliding cycles

05N10N

20N40N

Figure 4 Friction coefficient of Ni-Ti coating after the heattreatment sliding against SAE52100 steel balls as a function of slidingcycles

at a load of 05N keeps almost unchanged with increasingsliding cycles For the hard materials such as intermetalliccompounds and TiN the load is an important factor in thevariation of the antifriction and wear resistance A similarresult is observed in other literatures [22 23] At the sametime as listed in Table 1 the average friction coefficient andwear rate of the Ni-Ti coating before and after the heattreatment increase with increasing normal load which isrational since a larger normal load usually refers to moresevere adhesion scuffing and cracking of the coatings whichis in accordance with Archardrsquos law [24] And it is worthyof note that the coating via the heat treatment is helpful forgreatly decreasing the friction coefficient and wear rate ofthe coating which is attributed to the strengthening effectof the hard NiTi intermetallic compounds and TiN producedduring the heating process

Figure 5 shows the SEMmorphologies of the wear scar onthe steel ball sliding against the Ni-Ti coating after the heattreatment and Fe Ni and Ti element distribution thereonIt is seen that a great amount of wear debris was embeddedin the worn steel ball surface (see Figure 5(a)) while a smallamount of Ni-Ti intermetallic compounds and TiN trans-ferred from the coating was detected on the rubbing surfaceof the steel ball (see Figures 5(b) 5(c) and 5(d)) similar towhat has been reported by Chang et al [25] Subsequentlyit could be rational to suppose that the Ni-Ti coating afterthe heat treatment possesses better tribological propertiesin the presence of hard Ni-Ti intermetallic compounds andTiN with good wear resistance and somewhat solid lubricity[22 23]

The SEMmorphologies of the worn surfaces of the Ni-Ticoating after the heat treatment at different loads are shownin Figure 6 It is seen that the wear track of the as-deposited

Table 1 Comparison of friction andwear properties of two differentcoatings at different loads

Coatings Load (N) Average frictioncoefficient

Wear rate(times10minus9mm3Nm)

a 05sim40 065sim075 397sim482b 05 014 123b 10 018 185b 20 024 256b 40 028 327Note a refers to the as-deposited Ni-Ti coating and b refers to Ni-Ti coatingafter the heat treatment

coating before heat treatment shows signs of severe adhesionscuffing and plastic deformation and some large wear debrisis generated thereon (see Figure 6(a)) Different from beforeheat treatment the adhesion and scuffing on theworn surfaceof the coating after heat treatment were significantly abatedthough the scuffing and plastic deformation signs are stillvisible in this case (see Figure 6(b)) Besides the wear track isshallower and the size of the wear debris obviously decreasedon the worn surface of heated coating compared with the as-deposited coating This could be attributed to the enhancedabrasive action of the wear debris detached from the coatingduring the sliding This was rational since the hard Ni-Ti intermetallic compounds and TiN transferred onto therubbing surface of the counterpart steel ball could serve asthe spacers to prevent the rough contact between the coatingand the steel ball which thereby contributed to reduce thewear of the frictional pair In general the Ni-Ti coating afterthe heat treatment showed obvious different worn surfacemorphologies at different normal loads which correspondedwell with the different friction and wear behaviors thereat

4 Conclusions

It is feasible to prepareNi-Ti coatingmaking use of electrode-position by incorporating the to-be-co-depositedTi powdersin the Ni plating bath and heating the as-deposited Ni-Ticoating in N

2atmosphere Ni-Ti coating after heat treatment

possesses much higher hardness than the as-deposited Ni-Ti coating which is attributed to the strengthening effect ofthe hard intermetallic compounds includingNi

3TiNiTi and

NiTi2 and TiN phase produced during the heating process

Namely the as-deposited Ni-Ti coating has characteristictwo-phase structure-hexagonal Ti phase structure and cubicNi structure Different from the as-deposited Ni-Ti coatingthe coating after heat treatment is composed of the Ni-Tiintermetallic compounds coexisting TiN generated and avery small amount of Ni The newly generated intermetalliccompounds and TiN phase with good wear resistance andsomewhat solid-lubricity contributed to significantly increas-ing the tribological properties of Ni-Ti coating The Ni-Ticoating has much smaller friction coefficients and wear rateafter heat treatment than before heat treatment under the


(a)

Fe

(b)

Ni

(c)

Ti

(d)

Figure 5 SEM morphologies of (a) wear scar of the steel ball sliding against Ni-Ti coating after the heat treatment at 05N and 3Hz (b) Feelement (c) Ni element and (d) Ti element distribution thereon

(a) (b)

Figure 6 SEMmorphologies of the worn surfaces of Ni-Ti coatings (a) before heat treatment and (b) after heat treatment at a load of 40N

same test conditions which is attributed to the existenceof the hard NiTi intermetallic compounds and TiN andthe formation of a transfer layer on the counterpart surfaceduring sliding

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper


Acknowledgments

The work was supported by the National Natural Sci-ence Foundation of China for financial support (Grantno 51405477) and the Fundamental Research Funds forthe Central Universities (31920150002) The authors grate-fully acknowledge financial support from China ScholarshipCouncil

References

[1] M H Elahinia M Hashemi M Tabesh and S B BhadurildquoManufacturing and processing of NiTi implants a reviewrdquoProgress in Materials Science vol 57 no 5 pp 911ndash946 2012

[2] S M Toker D Canadinc H J Maier and O Birer ldquoEvaluationof passive oxide layer formation-biocompatibility relationshipin NiTi shape memory alloys geometry and body locationdependencyrdquo Materials Science and Engineering C vol 36 no1 pp 118ndash129 2014

[3] T Zhao Y Li Y Liu and X Zhao ldquoNano-hardness wearresistance and pseudoelasticity of hafnium implanted NiTishape memory alloyrdquo Journal of the Mechanical Behavior ofBiomedical Materials vol 13 pp 174ndash184 2012

[4] F M Braz Fernandes K K Mahesh R M S Martins R J CSilva C Baehtz and J Von Borany ldquoSimultaneous probing ofphase transformations in Ni-Ti thin film shape memory alloyby synchrotron radiation-based X-ray diffraction and electricalresistivityrdquoMaterials Characterization vol 76 pp 35ndash38 2013

[5] R E McMahon J Ma S V Verkhoturov et al ldquoA comparativestudy of the cytotoxicity and corrosion resistance of nickel-titanium and titanium-niobium shape memory alloysrdquo ActaBiomaterialia vol 8 no 7 pp 2863ndash2870 2012

[6] S A Fadlallah N El-Bagoury S M F Gad El-Rab R AAhmed and G El-Ousamii ldquoAn overview of NiTi shapememory alloy corrosion resistance and antibacterial inhibitionfor dental applicationrdquo Journal of Alloys and Compounds vol583 pp 455ndash464 2014

[7] C Zhang and Z N Farhat ldquoSliding wear of superelastic TiNialloyrdquoWear vol 267 no 1ndash4 pp 394ndash400 2009

[8] S Tria O Elkedim R Hamzaoui et al ldquoDeposition and charac-terization of cold sprayed nanocrystalline NiTirdquo Powder Tech-nology vol 210 no 2 pp 181ndash188 2011

[9] J Stella E Schuller C Heszliging O A Hamed M Pohl and DStover ldquoCavitation erosion of plasma-sprayed NiTi coatingsrdquoWear vol 260 no 9-10 pp 1020ndash1027 2006

[10] S K Sharma and S Mohan ldquoEffect of chemical treatment onsurface characteristics of sputter deposited Ti-rich NiTi shapememory alloy thin-filmsrdquo Journal of Alloys andCompounds vol592 pp 170ndash175 2014

[11] L Zhang C Xie and J Wu ldquoOxidation behavior of sputter-deposited TindashNi thin films at elevated temperaturesrdquoMaterialsCharacterization vol 58 no 5 pp 471ndash478 2007

[12] M M Verdian K Raeissi M Salehi and S Sabooni ldquoChar-acterization and corrosion behavior of NiTi-Ti

2Ni-Ni

3Ti mul-

tiphase intermetallics produced by vacuum sinteringrdquoVacuumvol 86 no 1 pp 91ndash95 2011

[13] G Tosun L Ozler M Kaya and N Orhan ldquoA study onmicrostructure and porosity of NiTi alloy implants producedby SHSrdquo Journal of Alloys and Compounds vol 487 no 1-2 pp605ndash611 2009

[14] J Y Xiong Y C Li X J Wang P D Hodgson and C E WenldquoTitaniumndashnickel shape memory alloy foams for bone tissueengineeringrdquo Journal of the Mechanical Behavior of BiomedicalMaterials vol 1 no 3 pp 269ndash273 2008

[15] I Napłoszek-Bilnik A Budniok B Łosiewicz L Pająk and EŁągiewka ldquoElectrodeposition of composite Ni-based coatingswith the addition of Ti orand Al particlesrdquo Thin Solid Filmsvol 474 no 1-2 pp 146ndash153 2005

[16] A Serek and A Budniok ldquoElectrodeposition and thermal treat-ment of nickel layers containing titaniumrdquo Journal of Alloys andCompounds vol 352 no 1-2 pp 290ndash295 2003

[17] Z Dong X Peng Y Guan L Li and FWang ldquoOptimization ofcomposition and structure of electrodeposited NindashCr compos-ites for increasing the oxidation resistancerdquo Corrosion Sciencevol 62 pp 147ndash152 2012

[18] V Hasannaeimi T Shahrabi and S Sanjabi ldquoFabrication ofNiTi layer via co-electrodeposition of nickel and titaniumrdquoSurface and Coatings Technology vol 210 pp 10ndash14 2012

[19] Y Zhao C Jiang Z Xu F Cai Z Zhang and P Fu ldquoMicrostruc-ture and corrosion behavior of Ti nanoparticles reinforcedNindashTi composite coatings by electrodepositionrdquo Materials ampDesign vol 85 pp 39ndash46 2015

[20] B Jonsson and S Hogmark ldquoHardness measurements of thinfilmsrdquoThin Solid Films vol 114 no 3 pp 257ndash269 1984

[21] J Panek and A Budniok ldquoProduction and electrochemicalcharacterization of Ni-based composite coatings containingtitanium vanadium or molybdenum powdersrdquo Surface andCoatings Technology vol 201 no 14 pp 6478ndash6483 2007

[22] M Abedini H M Ghasemi and M N Ahmadabadi ldquoTribo-logical behavior of NiTi alloy against 52100 steel and WC atelevated temperaturesrdquo Materials Characterization vol 61 no7 pp 689ndash695 2010

[23] E E Vera M Vite R Lewis E A Gallardo and J R Laguna-Camacho ldquoA study of the wear performance of TiN CrN andWCC coatings on different steel substratesrdquoWear vol 271 no9-10 pp 2116ndash2124 2011

[24] J F Archard ldquoElastic deformation and the laws of frictionrdquoProceedings of the Royal Society A Mathematical Physical andEngineering Sciences vol 243 no 1233 pp 190ndash205 1957

[25] C H Chang M C Jeng C Y Su and T S Huang ldquoA study ofwear and corrosion resistance of arc-sprayed Ni-Ti compositecoatingsrdquo Journal of Thermal Spray Technology vol 20 no 6pp 1278ndash1285 2011

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


parameter for examplemetal powder amount in the bath anddeposition current density on the chemical composition [18]and structure and corrosion properties of the coatings [19]and so far little work has been reported on the tribologicalproperties of Ni-Ti coatings via electrodeposition and heattreatment The as-deposited Ni-Ti coating was heat-treatedin pure N

2atmosphere which was aiming at increasing the

mechanical strength of the coating by the generation of Ni-Ti intermetallic compounds and TiN with good chemicalstability high microhardness and good wear resistance Thesurface morphologies structures and hardness and tribolog-ical properties of Ni-Ti coatings before and after the thermaltreatment were comparatively investigated

2 Materials and Methods

The plating bath is composed of 200 gsdotLminus1 NiSO4 35 gsdotLminus1

NiCl2 30 gsdotLminus1 Na

3C6H5O7 30 gsdotLminus1 H

3BO3 and 2 gsdotLminus1 Ti

powders Analytical reagents and distilled water were usedto prepare the electrodeposition solution The pH value ofthe solution is about 38 plusmn 01 and the electrodeposition timewas 30min The Ti powders (diameter of grains sim20120583mpurity 999) were dispersed in the electrolyte before platingThe electrodeposition was performed on a model 273Apotentiostatgalvanostat device (EGampG Princeton AppliedResearch) at 45∘C and a current density of 50mAsdotcmminus2

During the electrodeposition process the bathwas stirredby a magnetic stirrer at a stirring rate of 150 rpm to ensurea homogeneous suspension and facilitate transportation ofthe Ti suspension towards the substrate A platinum meshof 40 times 40mm2 was used as the anode and a saturatedcalomel electrode (SCE) was used as the reference electrodeA 1Cr18Ni9Ti steel plate of a size 10mm times 10mm times 1mm anda surface roughness less than 005 120583m were used as the cath-ode substrate The steel plate was sequentially ultrasonicallycleaned in ethanol acetone and distilled water for 10minactivated in a mixture of HCl and H

2SO4for 30 s washed in

distilledwater and then immersed immediately in the platingbath to deposit Ni-Ti coating

The as-deposited Ni-Ti coating with the thickness ofabout 110 plusmn 10 120583m was heated at 850∘C for 20 h in purenitrogen atmosphere using a muffle furnace with the heatingrate of 5∘Cmin The morphologies of the coatings wereobserved using a scanning electron microscope (JEOL JSM-5600LV) The phase structures of the coatings were ana-lyzed using an X-ray diffractometer (XRD Philips X1015840 Pert-MRD) The hardness of the coatings was measured on aVickersrsquo microhardness instrument at a load of 50 g for 5 sFive measurements were processed on each sample and theresults were averaged Since the measurement of hardness isalways influenced by the substrate the Jonsson andHogmarkmethod [20] was used to dissociate the contributions of thesubstrate and coating of measured hardnessThe deviation ofthe average hardness is less than 4The tribological proper-ties of the coatings reciprocally sliding against SAE52100 steelball (3mm) were tested on a UMT-2MT test rig (see Figure 1)in a ball-on-disk configuration The amplitude of the slidingwas 5mm a normal load was 05sim40N and a frequencywas 30Hz All the tribological tests were performed under

Counterface ball

Specimen holder

Dead load

Specimen

Ball holder

Figure 1 Diagrammatic sketch of the friction couple contact

dry friction condition at room temperature and in ambientair The friction coefficient was automatically continuouslyrecorded during the test

3 Results and Discussion

31 Structures and Morphological Characterizations of Ni-Ti Coatings Figure 2 shows the XRD patterns of the as-deposited Ni-Ti coatings before and after heat treatment Itis seen that the as-deposited Ni-Ti coating is characterizedby two-phase structure that is the nickel and titanium(Figure 2(a)) Namely the XRDpattern of these coatings con-firmed presence of themetal particles embedded into a nickelcrystalline matrix This also confirms that crystalline solidparticles of Ti could be embedded into the Ni matrix duringthe electrodepositionThe Ti phase has a hexagonal structureand the Ni has a cubic structure After heat treatment in N

2

atmosphere the coatings consist of Ni3Ti phase with some

minor phases of NiTi TiN andNiTi2and a sporadic phase of

Ni (Figure 2(b)) N2gas reacts with Ti particles on the coating

surface and simultaneously permeate through pores to reactwith Ti particles inside the coating to product TiN phaseunder N

2atmosphere and high temperature In other words

Ni and Ti in the as-deposited coatings almost transforminto Ni-Ti intermetallic compounds and TiN during the heattreatment process

The electrodepositionmechanism of Ni-Ti coating can beexplained by the adsorption of Ni ions on the Ti particlessurface Ni2+ ions which partly lack the hydration wrappingcan be electrochemically active and liable to move towardsthe cathode Because of the electrical conductivity of metal Tiparticles Ni experiences transition reaction and is depositedboth on the surface of the subtrate and on Ti particles whichallows the generation of the composite coating structure [1618 21]

Figure 3 shows the SEM morphologies of the Ni-Ticoating before and after the heat treatment It is seen that as-deposited Ni-Ti coating has a particulate-like structure andgranular morphology (Figure 3(a)) which indicates that thecodeposited Ti particulates were uniformly distributed in theNi matrix of the coating It was also found that the presenceof metal particles embedded into the nickel matrix distinctlyenlarge the real surface of the coatings This is because thegrowth becomes more 3D in character leading to dendrites


20 30 40 50 60 70 80 90

5000

10000

15000

20000

25000

30000

Ο

NiΟ Ti

Ο

Inte

nsity

(cps

)

2120579 (deg)

nabla

nabla

nabla

nabla

(a)

30 40 50 60 70 80 90

5000

10000

15000

20000

25000

30000

35000

bullloz

lozbullbull

Inte

nsity

(cps

)

bull NiTiloz

TiNNi

loz

bull

2120579 (deg)

Ni3Ti

NiTi2

nablanabla

nabla

Δ

Δ

Δ ⧫

⧫

⧫

⧫

(b)


(a) (b)



2which leads


2cannot completely



3Ti NiTi and NiTi

2




0 400 800 1200 1600 200000

01

02

03

04

05

06

Fric

tion

coeffi

cien

t

Sliding cycles

05N10N

20N40N










4 Conclusions




3TiNiTi and




(a)

Fe

(b)

Ni

(c)

Ti

(d)


(a) (b)






Acknowledgments


References













2Ni-Ni

3Ti mul-






















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20 30 40 50 60 70 80 90

5000

10000

15000

20000

25000

30000

Ο

NiΟ Ti

Ο

Inte

nsity

(cps

)

2120579 (deg)

nabla

nabla

nabla

nabla

(a)

30 40 50 60 70 80 90

5000

10000

15000

20000

25000

30000

35000

bullloz

lozbullbull

Inte

nsity

(cps

)

bull NiTiloz

TiNNi

loz

bull

2120579 (deg)

Ni3Ti

NiTi2

nablanabla

nabla

Δ

Δ

Δ ⧫

⧫

⧫

⧫

(b)


(a) (b)



2which leads


2cannot completely



3Ti NiTi and NiTi

2




0 400 800 1200 1600 200000

01

02

03

04

05

06

Fric

tion

coeffi

cien

t

Sliding cycles

05N10N

20N40N










4 Conclusions




3TiNiTi and




(a)

Fe

(b)

Ni

(c)

Ti

(d)


(a) (b)






Acknowledgments


References













2Ni-Ni

3Ti mul-






















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 400 800 1200 1600 200000

01

02

03

04

05

06

Fric

tion

coeffi

cien

t

Sliding cycles

05N10N

20N40N










4 Conclusions




3TiNiTi and




(a)

Fe

(b)

Ni

(c)

Ti

(d)


(a) (b)






Acknowledgments


References













2Ni-Ni

3Ti mul-






















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a)

Fe

(b)

Ni

(c)

Ti

(d)


(a) (b)






Acknowledgments


References













2Ni-Ni

3Ti mul-






















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Acknowledgments


References













2Ni-Ni

3Ti mul-






















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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