lable at ScienceDirect

Vacuum 104 (2014) 41e46

Contents lists avai

Vacuum

journal homepage: www.elsevier .com/locate/vacuum

Deposition of superelastic composite NiTi based films

Wolfgang Tillmann*, Soroush Momeni 1

Institute of Materials Engineering, Technische Universität Dortmund, 44227 Dortmund, Leonhard-Euler-Str 2, NRW, Germany

a r t i c l e i n f o

Article history:Received 19 August 2013Received in revised form16 December 2013Accepted 18 December 2013

Keywords:Thin filmsShape memory alloysNiTiSuperelasticitySelf-healing

* Corresponding author. Tel.: þ49 231 755 2581.E-mail addresses:wolfgang.tillmann@udo.edu (W.

tu-dortmund.de (S. Momeni).1 Tel.: þ49 231 755 6113.

0042-207X/$ e see front matter � 2014 Published byhttp://dx.doi.org/10.1016/j.vacuum.2013.12.010

a b s t r a c t

In recent years, NiTi shape memory alloys (SMA) thin films have been widely used as promising high-performance materials in the field of biomedical and microelectromechanical (MEMS) systems. How-ever, there are still important problems such as their unsatisfactory mechanical and tribological prop-erties including a limited hardness and wear resistance. This study aimed at deposition of layeredcomposite thin films made of NiTi and TiCN thin films on Si (100) substrate by means of DC magnetronsputtering. Subsequently, microstructures, mechanical properties and shape memory behavior of thesebilayers were investigated using Nanoindentation, X-ray diffraction (XRD), scanning electron microscopy(SEM) and differential scanning calorimetry (DSC). The results of this study confirmed that the presenceof TiCN layer on NiTi thin film modifies its mechanical properties while maintaining the shape memoryeffects. The initial findings of this research work are suggestive of the potential for fabrication of self-healed composite NiTi based films.

� 2014 Published by Elsevier Ltd.

1. Introduction

NiTi shape memory alloy (SMA) thin films have attracted lots ofattention because of their unique properties such as shape memoryeffect (SME), superelasticity (SE), large deformation compatibility,high damping capacity and biocompatibility. These propertiesmake them promising candidates to be widely used in biomedicaland microelectromechanical systems (MEMS) [1e9]. The brilliantfeature of shapememory and/or superelastic behavior, with respectto tribological phenomena, is that large reversible non-linearstrains can occur without the generation of lattice deformation.This “self-healing” effect can be employed to engineer surfaceswith excellent tribological properties. It can be done evenwhen thematerial is present only as a surface coating [10,11]. Nevertheless,they have some application limitations due to their undesirablemechanical properties such as limited hardness, poor wear resis-tance and high coefficient of friction [12e14]. Several surfacemodification techniques have been used to improve surface prop-erties of NiTi alloys such as nitrogen ion implantation [15] and lasersurface treatment [16]. The main disadvantages of these techniquesare the degradation of shape memory effect and possibility ofamorphous phase formation.

Tillmann), soroush.momeni@

Elsevier Ltd.

Recently Kumar et al. aimed at modifying surface properties ofNiTi thin films by deposition of a TiN coating as a protectivelayer [17]. Within this research work, thin protective layers of TiN(140 nme300 nm) were deposited on thicker NiTi layers (2 mme

3.5 mm). The presence of a hard and adherent TiN coating layercould modify mechanical and tribological properties of NiTi thinfilms. However, these hard layers are thin (less than 20% of the totalthickness) and can be easily peeled off. In addition, TiN coating hasseveral disadvantages in terms of tribological properties like rela-tively higher friction coefficient and low oxidation resistance atelevated temperatures.

In another effort for improvement of surface properties of NiTimaterials, Zhang et al. deposited CrN coating layers (thicknessvarying between 1.7 mm and 3.9 mm) on 15 and 21 mm thick NiTithin film [18]. Nevertheless, in this case, there is a high possibility ofspallation of the coating due to high total thickness. Moreover, sucha coating system with this total thickness (22.8 mme24.9 mm)cannot be employed in MEMS applications since it reduces theirfrequency response and efficiencies.

As an alternative solution, TiCN coating layers have beenintroduced during this research work for improving mechanicaland tribological properties of shape memory NiTi thin films andwith respect to the self-heal composite NiTi based films. In TiCNcoatings, incorporation of carbon atoms in TiN increases hardnessand decreases coefficient of friction of the coatings [19]. However,TiCN coatings exist on a broad composition range where the phaseis stable (face centered cubic) but mechanical properties aredifferent. Furthermore, it has been verified that the hardness of

W. Tillmann, S. Momeni / Vacuum 104 (2014) 41e4642

TiCN coatings increases with the amount of carbon content in thefilm [20e22].

Therefore, during the current research work, carbon rich TiCNcoatings have been deposited, developed and optimized by meansof a DC magnetron sputtering and through changing flow rates ofthe nitrogen and acetylene process gases. The properties of un-derneath NiTi layer must be retained by addition of TiCN as aprotective layer. Consequently, TiCN thin films have been depositedwith various thicknesses on NiTi thin films of approximately500 nm in order to find the optimum TiCN/NiTi thickness ratio.Furthermore, a four-layer coating consisting of TiCN and NiTi layerswas deposited in order to study deposition rate variation of NiTilayer on Si substrate and on TiCN coating layer (uniformity ofcoating layers).

2. Experimental

Monolayer NiTi, bilayer NiTi/TiCN and four-layer NiTi/TiCN thinfilms were deposited on silicon (100) substrate by means of a DCmagnetron sputtering device (CC800sinox, CemeCon AG, Ger-many). Two NiTi alloy targets (51 at.% TieNi) and Ti targets (with apurity of 99.99%) have been employed and the argon pressure usedwas 350 mPa. The sample holder was rotated on a horizontal tableduring sputtering in order to achieve a uniform film composition.The target to substrate distancewas fixed at approximately 9.5mm.Firstly, NiTi thin films were deposited at substrate temperature of425 �C and no post annealing process was done after deposition.The sputtering power applied for NiTi targets was 1400 W. Sec-ondly, NiTi targets were turned off and Ti targets were turned on inorder to deposit TiCN protective layers at substrate temperature of250 �C. For this deposition, two different reactive gases of N2 andC2H2 were used inside of the coating chamber. The flowing rate ofN2 gas was constant while various flowing rates have been used forC2H2 gas in order to adjust carbon content of the TiCN layer. Twobilayer coating systems of NiTi/TiCN have been deposited withdifferent TiCN layer thickness (1600 nm for sample B1 and 2175 nmfor sample B2). The NiTi layer thickness in bilayers and four layerscoatings is about 500 nm. Various TiCN layer thicknesses have beendeposited by changing deposition time of TiCN layers (45 min forsample B1 and 75 min for sample B2). The detailed description ofthe deposited thin films is presented in Table 1. The phase structureand the crystallographic planes of thin films were analyzed byemploying X-ray diffraction using Cu Ka radiation and 9� incidentangle (D8 Advance, BRUKER AXS, Germany). The thin filmmorphology and thickness were analyzed on a fracture cross-section of coated samples by means of a field emission scanningelectron microscope (Jeol JXA840, JSM 35, Japan), while composi-tion of coatings was determined using energy-dispersive X-rayspectrometry (EDX) with an electron acceleration voltage of 20 kVand a beam current of 15 nA. All samplingwas done by analyzing anarea and not a point composition. Phase transformations of freestanding NiTi coatings were characterized using a differentialscanning calorimeter (DSC 2920 CE from TA Instruments). DSCspecimens with a mass of 20 mgwere heated and cooled at the rateof 10 K/min over a temperature range of �150 to 150 �C.

Table 1Different thin films deposited as well as their corresponding thicknesses.

Sample ID Materials Thickness

A NiTi 3.4 mmB1 NiTi/TiCN 600 nm/1300 nmB2 NiTi/TiCN 530 nm/2175 nmC (NiTi/TiCN)2 560 nm/1038 nm

500 nm/1038 nm

The hardness and young’s modulus of coatings were measuredby a depth-controlled nanoindenter XP (MTS Nano instrument,USA) with a penetration depth of 10% of coating thickness in orderto minimize the effect of substrate hardness on the measurement.During nanoindentation measurements, a berkovic tip made ofconductive diamond has been employed. The method used in thisresearch work is called “G-series CSM Hardness, Modulus for ThinFilms”. By employing this method, the indenter penetrates thesurface at a rate determined by strain rate target of (0.051/S). Whenthe surface penetration reaches the depth limit (150 nm), the loadon the indenter is held constant for 100 s. The indenter is thenwithdrawn from the sample (but not completely) at a rate equal tothe maximum loading rate. When the load on the sample reaches10% of the maximum load on the sample, the load on the sample isheld constant for 100 s. The indenter is then withdrawn from thesample completely and the sample is moved into position for thenext indentation. For each sample 49 indentations (7X7 squarearrays) have been performed.

3. Results

3.1. Morphology of thin films

The atomic percentage of nickel and titanium needed to bewithin a narrow range to obtain a shape memory alloy. Thereforeabout an equal amount of nickel and titanium is needed. However,employing a target setup of 50% titanium and 50% nickel will notlead to a stoichiometric NiTi thin film, because titanium has a lowersputtering yield comparing to nickel. As a result, two titanium richNiTi targets (51.82 at.% Ti and 48.18 at.% Ni) were used to produceNiTi thin films. The elemental composition of NiTi films wasdetermined by EDX surface analysis and its results are shown inFig. 1a and b. It clearly shows that the deposited NiTi thin film is inthe composition range required for shape memory effect.

For deposition of carbon rich TiCN thin films two reactive gasesof N2 and C2H2 were used. It is possible to determine the amount ofcarbon and nitrogen in TiCN coatings by adjustment of flowingrates of C2H2 and N2 gases respectively. Consequently, in order tooptimize composition of TiCN coatings, different flowing rates ofreactive gases have been employed.

Fig. 1c and d illustrate the elemental spectrum and compositionof deposited TiCN films obtained by EDX. It confirms that thedeposited film has a chemical composition in the form C þ N i50 at.%, Ti< 50 at.%.). It is worthy to note that care must be taken inall stoichiometric analyses, because EDX has low reliability for lightelements such as carbon and nitrogen concentrations. However, theincrease in carbon content of each film could be controlled byvarying flowing rate of the C2H2 gas under a constant applied po-wer for Ti targets and flowing rate of the N2 gas.

It was also realized, based on the analyses of fractures made byfield emission scanning electron microscopy (FESEM), that thedeposited coatings are characterized by dense, compact structure.There are no pores, fractures and discontinuities. Due to thecontrast between the different layers, an identification of layeredstructures of the films could be accomplished successfully.

Fig. 2 a shows the FESEM images of the fractured cross-sectionof four layered NiTi/TiCN coating (sample C). The thickness of thetotal film is 3.1 mmwhile the thicknesses of the first and second NiTilayers are 563 nm and 495 nm respectively. The thickness of TICNcoating is constant in the first and second layer and equal toapproximately 1000 nm. It clearly confirms that the deposited(NiTi/TiCN)2 coating possesses a well-defined and uniform peri-odicity in its layered structure. According to thickness of the layersand deposition time, the deposition rates of the NiTi and TiCNlayers are 1.3 nm/min�1 and 35 nm/min�1 respectively. Fig. 2b and

Fig. 1. a) EDX spectra for NiTi coatings b) elemental composition of NiTi coatings c) EDX spectra for TiCN coatings d) elemental composition of TiCN coatings.

W. Tillmann, S. Momeni / Vacuum 104 (2014) 41e46 43

c show bilayer coating systems of NiTi/TiCN. The white phase inFig. 2b (below NiTi interlayer) is a part of the silicon wafer.

Furthermore, it can be observed in all of the FESEM images thatthere are glass-like and columnar structures within the depositedNiTi/TiCN films. This can be clearly seen in Fig. 2d which shows themicrostructure of the NiTi/TiCN coating system (sample B1) athigher magnification. The NiTi layers present the glass-like struc-ture which has no characteristics and is relatively smooth. As it canbe seen, the microstructure of the NiTi layer is quite different to the

Fig. 2. Fracture FESEM images of a) NiTi/TiCN four layer coating system b) NiTi/TiCN bilayer cbilayer coating system (sample B1) with higher magnification.

columnar structures of TiCN layers. Such a difference is attributedto the different materials used in each layer and also to differentsputtering temperatures during the deposition of the layers. Duringthe sputtering of NiTi layers the temperature was 425 �C while itwas 250 �C for sputtering of TiCN layers. As it has been shown in allof the FESEM images, no micro cracks and delamination exist be-tween the filmesubstrate interface and layerelayer boundary ofthe thin films, which can be a sign of good bonding strength be-tween individual layers.

oating system (sample B1) c) NiTi/TiCN bilayer coating system (sample B2) d) NiTi/TiCN

Fig. 4. XRD pattern of NiTi thin films at RT.

W. Tillmann, S. Momeni / Vacuum 104 (2014) 41e4644

3.2. Phase transformation analysis of NiTi thin film

The phase transformation temperatures of NiTi thin films areconventionally determined by the differential scanning calorim-etry. Fig. 3 shows the DSC measurement of deposited NiTi thin film.In this measurement, exothermic and endothermic peaks can beobserved clearly at the martensitic and reverse martensitic trans-formation on cooling and heating, respectively.

It was shown that the transformation to the parent austeniticphase starts (As) at �2.2 �C and finishes transforming intoaustenite (Af) at 55.7 �C. As the temperature decreases, thetransformation back to martensite phase starts (Ms) at 53.7 �C.Phase transformation to fully martensite ends (Mf) at 25.8 �Cwhile cooling down the coating. The DSC plot uncovered thetransformation to austenite was a two-step transformation. Thefirst step begins at the austenite start (As) temperature of �2.2 �Cand the second step was at 28 �C. The two hypotheses for the twosteps transition are a type of R-phase and the presence of pre-cipitates. The first hypothesis is a precursor transition before theaustenite phase. This alternative phase is called R-phase and is alattice distortion that can occur before a transition. Such a DSCcurve corresponds with a DSC measurement that has been doneby Miyazaki et al. [23]. They found such a two steps curve for aTi-51.9 at.% Ni alloy thin film that was sputtered at room tem-perature and subsequently aged at 500 �C for 1 h. They called thefirst and second peaks A* and RA* representing the reversetransformation from martensite to R-phase and from R-phase toaustenite, respectively. However, the R-phase is more commonlyfound before the transition from austenite to martensite. Basedon the second hypothesis, the elongated transition could be fromNi4Ti3 precipitates. These precipitates can elongate the transitiontemperature as observed from the DSC data and can cause a two-peak transition [24]. The Ni4Ti3 precipitates are also consistentwith the overall nickel rich composition.

3.3. X-ray diffractometry

The XRD pattern in Fig. 4 shows that NiTi thin films werecompletely crystallized during sputtering due to the simulta-neous heating. Three obvious diffraction peaks at 2q ¼ 42.3�, 62�

and 78.2�, respectively, correspond to (110), (200) and (211)lattice orientations of austenite B2 structure of NiTi thin films.The existence of a weak and broad Ni4Ti3 peak at 2q ¼ 37.8�

implies slightly non-equilibrium precipitations reactions duringsputtering.

Fig. 5 shows a XRD pattern of the four layer coating system (NiTi/TiCN)2. All peaks corresponding to the (111), (200), (220), (311),(222), (420) plane of the face-centered cubic TiCN phase and

Fig. 3. DSC spectra of NiTi thin film.

austenite NiTi (110), (200), (211) phase are observed in the fourlayer thin film. The width of XRD peaks is usually representative ofcrystallite size, defects (strain, disorder). As a result, the existence ofsuch broad XRD peaks might be ascribed to the layered structure ofthe (NiTi/TiCN)2 coating system. Moreover, except of (111) peak ofTiCN at 2q of 36.5�, all of its peaks overlap with NiTi peaks. It couldbe another reason for formation of these broader peaks withreduced intensity. By comparing intensity of peaks, it can beconcluded that crystalline structure of this coating system is pref-erentially oriented along (110) plane of austenite NiTi as well as(200) plane of TiCN coating layers.

3.4. Mechanical properties

The nanoindentation test is a promising method for character-ization of nanoscale superelasticity (SE) [25]. The superelasticitybehavior in NiTi-based thin films introduces their inherent capacityto undergo large deformations without permanent surface damage,which is known as self-healing behavior.

The indentation response mechanism of the NiTi shape memoryalloys is quite complicated because of different possible deforma-tion modes. They can be deformed elastically or plasticallydepending on the test temperature, amount of applied stress andthe geometry of employed indenter.

In the present work, indentation experiments of NiTi thin filmswere conducted at room temperature (RT) first. However, accordingto the DSC curve of NiTi thin film, the austenite finish temperatureof the NiTi film is 53.7 �C. Consequently, in order to have a mea-surement at austenite phase of NiTi, the specimenwas heated up to

Fig. 5. XRD pattern of four layer NiTi/TiCN coating system.

Fig. 6. Young’s modulus versus load on the NiTi thin films at RT and 80 �C.

Fig. 8. Hardness and elastic modulus of NiTi, (NiTi/TiCN) B1 and (NiTi/TiCN) B2 atroom temperature and 80 �C.

W. Tillmann, S. Momeni / Vacuum 104 (2014) 41e46 45

80 �C which is higher than Af temperature. Subsequently, nano-indentation measurement was done at this temperature. Theaverage of measured values for hardness and Young’s modulus ofthe NiTi thin film at RT are 4.51 � 0.91 and 83.4 � 9.5 respectively.In addition, the calculated values of hardness and young’s modulusat 80 �C are 6.44 � 0.95 and 97.7 � 8.9. These measured values arequite comparable with those in Ref. [26]. From these values, it canbe realized that the elastic modulus of thin film increases byincreasing the temperature above Af. The increase in the value ofmodulus proves the phase change has occurred and that it can bemeasured by in situ heating methods. In other words, such an in-crease is due to the fact that the film transforms entirely toaustenite phase at 80 �C which evidences a superelasticitybehavior.

Although XRD pattern of NiTi thin films at room temperatureshows typical austenite peaks, there should be considerableamount of martensite or R-Phase in the coating which will trans-form to austenite upon heating. Fig. 6 shows Young’s modulus as afunction of applied load on the NiTi thin film at RT and 80 �C. Itclearly shows that after “running-in” period the specimen at 80 �Cshows always higher Young’s modulus comparing to room tem-perature (RT).

With the addition of TiCN layer to NiTi thin film, hardness andelastic modulus values increased significantly to 11.53 � 0.97 GPaand 174 � 5.45 GPa, respectively for the NiTi/TiCN bilayer coatingsystem (sample B1) at RT. In order to investigate whether the phasetransformation exists still in the bilayer coating or not, the inden-tation measurement of the specimen was done also at 80 �C. Theresults show that hardness and young’s modulus of this specimen

Fig. 7. Modulus versus load on the NiTi/TiCN (sampleB1) thin films at RT and 80 �C.

increases to 14.37 � 5.45 GPa and 186.9 � 8.2 GPa, respectively atan elevated temperature of 80 �C. Such an increase in the measuredvalues is a consequence of the superelasticity effect induced by theaustenitic NiTi layer underneath. Furthermore, it could be an effectof the higher hardness and young’s modulus of the austenite NiTiphase on the values of TiCN coating layer. The induced super-elasticity is necessary for a self-healing behavior of NiTi based thinfilms. Fig. 7 shows young’s modulus as a function of applied load onthe NiTi/TiCN thin film (sample B1) at RT and 80 �C. As it can beseen, by applying same loads, this coating system possesses higherelastic modulus at 80 �C comparing to room temperature.

Furthermore, nanoindentationmeasurement was performed forNiTi/TiCN coating system (sampleB2) at RT and 80 �C. Themeasured values of hardness and Young’s modulus of all samples atRT and 80 �C are shown in Fig. 8.

As it can be seen for this coating, the values of hardness andyoung’s module change slightly with increasing temperature. Inaddition, Fig. 9 shows Young’s modulus as a function of applied loadon this thin film at RT and 80 �C. It is quite obvious that this coatingsystem shows more or less a similar elastic deformation at RT and80 �C. In other words, by employing identical loads in the range of4 mNe7 mN, there is no significant difference in elastic modulusvalues of this coating at RT and 80 �C. Such a behavior confirms thatsuperelasticity property of austenite NiTi at 80 �C couldn’t becombined with upper TiCN layer and consequently couldn’t lead toreduction of plastic deformation (or increase in elastic deforma-tion). The reason is that thickness of TiCN layer is 2175 nmwhich isapproximately five times the thickness of NiTi layer. Such a highthickness inhibits the induction of austenite phase properties andprevents the formation of combined properties of lower layer NiTiand upper layer TiCN.

Fig. 9. Modulus versus load on the NiTi/TiCN (sampleB2) thin films at RT and 80 �C.

W. Tillmann, S. Momeni / Vacuum 104 (2014) 41e4646

It must be noted that in nanoindentation measurements per-formed, a Berkovic tip which is a sort of sharp tip, has beenemployed. Characterization of superelasticity behavior can bechallenging by employing a sharp tip since the plastic deformationdue to dislocation movement underneath a Berkovic tip is domi-nant over phase transformation [27]. In other word, the strainsinduced by this tip exceed the superelastic limit and the resultingdeformation is dominantly plastic. Therefore, spherical shaped tipshave been recently introduced to characterize nanoscale super-elasticity behavior of NiTi thin films [28].

Additional experiments on composite NiTi thin films, usingspherical tips, are in progress by authors to clarify the indenta-tion recovery ability in sputtered films. However, the resultspresented here show clearly that such a capability exists and thisself-healing effect will be obtainable for composite NiTi thinfilms.

4. Conclusion

Within this research work, a carbon-rich TiCN has been devel-oped and optimized. Subsequently, it was successfully depositedon a NiTi film with a thickness of 500 nm using a magnetronsputtering device. Two bilayer coating systems were depositedusing upper layer of TiCN with thicknesses of 1228 nm and2175 nm. In addition, a four-layer coating system of NiTi/TiCN hasbeen deposited with constant thickness of the NiTi and TiCN layers.Obtained results are suggestive of a potential for fabrication of self-healing superelastic thin films. Moreover, the following points areemphasized:

1. In deposition of TiCN coatings, there is a direct relation betweenamount of carbon in the coating and the flowing rate of C2H2reactive gas. It happens when the flowing rate of N2 and sput-tering power of Ti targets are constant.

2. DSC analysis proves the existence of shape memory effect of thedeposited NiTi thin film and provides information about thetransformation temperatures.

3. XRD patterns of NiTi thin films shows the mostly austenitephasewith residual amount of Ni4Ti3 precipitation. It shows thatthe film has been fully crystallized due to the heating during thesputtering.

4. TiCN thin film can be successfully deposited on NiTi thin filmwithout any significant phase disturbance. Moreover, four layercoating system of NiTi/TiCN shows a well-defined and uniformperiodicity in its layered structure.

5. Addition of TiCN layer on austenite NiTi leads to a new gener-ation of self-healing composite NiTi based films by benefitingproperties of each of the single layers (superelasticity of theaustenite NiTi as well as hardness and Young’s modulus of theupper TiCN layer).

References

[1] Wayman CM. Prog Mater Sci 1992;36:203.[2] Kahn H, Huff MA, Heuer AH. J Micromech Microeng 1998;8:p.213.[3] Wie ZG, Sandstorm R, Miyazaki S. J Mater Sci 1998;33:3743.[4] Wolf RH, Heuer AH. J Microelectromech Syst 1995;4:p.206.[5] Krulevitch P, Lee AP, Ramsey PB, Trevino JC, Hamilton J, Northrup MA.

J Microelectromech Syst 1996;5:270.[6] Fu YQ, Du HJ. Surf Coat Technol 2002;153/1:206.[7] Miyazaki S, Hashinaga T, Ishida A. Thin Solid films 1996;281e282:364.[8] Miyazaki S, Ishida AQ. Mater Sci Eng A 1999;273e275:106.[9] Krulevtich P, Ramsey PB, Makawiechi DM, Lee AP, Northrup MA, Johnson GC.

Thin Solid Films 1996;283:67.[10] Grummon DS, Nam S, Chang L. Proc Mat Res Soc 1992;246:259e64.[11] Hou Li, Grummon DS. Scr Met 1995;33:989e95.[12] Hu SB, Tu JP, Mei Z, Li ZZ, Zhang XB. Surf Coat Technol 2001;141:174.[13] Tu JP, Zhu LP, Zhao HX. Surf Coat Technol 1999;122:176.[14] Aliofkhazraei M, Sasabour Rouhaghdam A. Surf Coat Technol 2010;205:S51.[15] Zhao X, Cai W, Zhao L. Surf Coat Technol 2002;155:236.[16] Cui ZD, Man HC, Yang XJ. Surf Coat Technol 2002;192:347.[17] Kumer A, Kaur D. Surf Coat Technol 2009;204:1132e6.[18] Zhang Y, Chen YT, Grummom DS. Sur Coat Technol 2007;202:998e1002.[19] Polcar T, Kubart T, Novák R, Kopecký L, �Siroky P. Sur Coat Technol 2005;193:

192e9.[20] Huang SW, Ng MW, Samandi M, Brandt M. Wear 2002;252:566e79.[21] Randhawa H. Cathodic arc plasma deposition of TiC, TiCxN1�x films. Thin Solid

Films 1987;153:209e18.[22] Bergmann E, Kaufmann H, Vogel J, Schmid R. Ion plated titanium carbonitride

films. Surf Coat Technol 1990;42:237e51.[23] Miyazaki S, Fu YQ, Huang WM. Thin film shape memory alloys; 2009. pp. 21e

2. Cambridge, New York.[24] Fan G, Chen W, Yang S, Zhu J, Ren X, Otsuka K. Acta Mater 2004;52:4351.[25] Ni W, Cheng YT, Lukitsch M, Weiner AM, Lev LC, Grummon DS. Wear

2005;259:b842e8.[26] Huang Xu, Nohava Jiri, Zhang Bin, Ramirez AG. Int J Smart Nano Mater

2011;2(1):39e49.[27] Muir Wood AJ, Sanjabi S, Fu YQ, Barber ZH, Clyne TW. Surf Coat Technol

2008;202:3115e20.[28] Ni W, Cheng YT, Grummon DS. J Phys IV France 2003;112.