Surface and Coatings Technology 156(2002) 170–175

0257-8972/02/$ - see front matter� 2002 Elsevier Science B.V. All rights reserved.PII: S0257-8972Ž02.00124-X

Deformation behavior of titanium nitride film prepared by plasmaimmersion ion implantation and deposition

N. Huang *, G.J. Wan , Y. Leng , Y.X. Leng , H. Sun , P. Yang , J.Y. Chen , J. Wang , P.K. Chua, a b a a a a a c

Department of Materials Engineering, Institute of Biomaterials Surface Engineering, Southwest Jiaotong University, Chengdu,a

Sichuan 610031, PR ChinaDepartment of Mechanical Engineering, Hong Kong University of Science and Technology, Hong Kong, PR Chinab

Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, PR Chinac

Abstract

Plasma immersion ion implantation and deposition(PIIID) provides a novel approach to fabricate high quality films by meansof utilizing particle filtrated metal plasma and varying acceleration pulse voltages. In this work, investigation on plastic deformationof TiN films synthesized by PIIID was performed by pulling the TiN film-coated stainless steel sheet samples. The surfacemorphology during the pulling was observed in situ by scanning electron microscopy. No delaminating, peeling or cracking werefound on the coating surfaces. The structure of the films was identified by transmission electron microscopy and atom forcemicroscopy. It is considered that the excellent deformation behavior of the TiN film was related with the nanocrystal structure ofthe films and the broader filmymatrix interface achieved by the PIII process.� 2002 Elsevier Science B.V. All rights reserved.

Keywords: Deformation behavior; Titanium nitride film; Plasma immersion ion implantation

1. Introduction

During the past two decades, hard compounds basedon the TiN system have received a great attention forx

wear-resistant coatings for cutting tools, and other wear-sensitive parts for machines and also as medical implantdevicesw1x due to their high hardness, refractory natureand relative chemical inertness. Many deposition tech-niques have been developed and used in industry toproduce TiN films on appropriate substrates. The tech-niques include physical vapor deposition(PVD) (includ-ing DC and RF sputtering, magnetron sputtering, ionplating, electron beam evaporation, etc.), chemical vapordeposition(CVD), plasma assisted chemical vapor dep-osition (PACVD), etc. The hardness of the films can beas high as over 2000 Hv. However, the binding strengthof TiN films to matrixes and the toughness of the filmsare not high enough to meet the needs of some appli-cations w2,3x. Techniques combining vapor depositionand ion bombardment, such as ion beam assisted depo-

*Corresponding author. Tel.:q86-28-7600728; fax:q86-28-7600728.

E-mail address: huangnan@sc.homeway.com.cn(N. Huang).

sition (IBAD), have been proved to possess betterproperties than PVD, CVD and PACVD due to a widerfilm–matrix interface, modification of the structure andinternal stress in the films. Improvement in the fatiguelimit of the Ti alloy with IBAD-coated TiN films hasbeen found in our previous researchw4x. However, theapplication of IBAD is limited by its line-of-sight natureand can only be used on surfaces of simple shape. Theplasma immersion ion implantation and deposition(PIIID) technique developed in the last decade hasshown to be potential for industry applications becauseit does not have the line-of-sight shortcoming. In thispaper, the plastic deformation behavior of a TiN filmsynthesized by PIIID on stainless steel was investigated.

2. Experimental

To prepare tensile samples, stainless steel sheets(0Cr18Ni9Ti, yield strength of approx. 200 MPa) werefirst cut into the shape as shown in Fig. 1. The thicknessof the samples was 0.7 mm. The surfaces of the sampleswere mechanically polished to the final roughness of0.02 mm and then cleaned in an ultrasonic bath withacetone, ethanol, and distilled water separately. Then the

171N. Huang et al. / Surface and Coatings Technology 156 (2002) 170–175

Fig. 1. The shape of tensile samples.

Fig. 2. The morphology of TiN film surface obtained using AFM.

Table 1Instrumental parameters of PIIID for synthesis of the TiN film

Vacuum arc Pulse repetition rate(Hz) 65metal plasma Pulse width(ms) 1source Arc current(A) 180

Nitrogen partial 1.2pressure(=10 Pa)y2

RF power(W) 600 Fig. 3. Composition profile of the TiN film on silicon wafer obtainedusing AES.

samples were fixed on a sample hold and mounted intothe sample stage of a PIIID system. The PIIID devicewas equipped with several plasma generating devices,including radio frequency(RF) discharge, hot-filamentdischarge, and vacuum arc metal plasma source. A Ticathode of 14 mm in diameter was mounted on themetal vacuum arc plasma source. The sample hold wasvertical to the metal source at the distance of 500 mmbetween the titanium cathode and the sample hold.To synthesize the TiN film, the work chamber of

PIIID was first vacuumed to a pressure of 8=10 Pa,y4

then Ar gas was introduced into the chamber at a rateof 5 cm ymin. Ar plasma of 2.5=10 Pa work pressure3 y2

was generated by a 1000-W RF discharge. A DC voltageof 1000 V was applied on the sample stage for 10 minto clean the samples by sputtering. N plasma was2

generated by 600-W RF discharge and at the same time,titanium plasma was generated in the metal arc sourceand was introduced into the vacuum chamber via amagnetic duct to eliminate deleterious macro-particles.In order to increase the adhesion between the film andsubstrate, a 3-kV pulse voltage of 10 kHz frequencyand 5-ms pulse width was applied to the samples in thefirst 10 min. Finally the voltage on the sample wasadjusted to a 50-V DC for 10 min to deposit the TiNfilm on the samples. The instrumental parameters of thePIIID equipment are listed in Table 1. The thickness ofthe TiN films was measured to be 250 nm using analpha-step profilemeter.Transmission electron microscopy(TEM) was used

to investigate the microstructure of the TiN film. To

prepare the TEM specimen, a stainless steel sheet wascut into 3-mm discs and ground to 0.7 mm in thickness.One side of the specimen was mechanically polishedthe same as the tensile samples and coated with a TiNfilm together with the tensile samples. After coating theTiN film, the 3-mm samples were further ground andpolished from the uncoated surfaces down to a thicknessof ;0.07 mm, and finally polished using ion mill(DuoMill Model 600-DIF) to thin enough for TEMobservation. A H-700H TEM, voltage 200 kV, was usedto investigate the film structure.Surface morphology of the film on the silicon wafer

was investigated by an atomic force microscopy(AFM,Autoprobe CP). The composition profile in depth wasdetected using Auger electron spectroscopy(AES, PHI650 SAM).Scanning electron microscopy(SEM) was used to

investigate the deformation behavior of the TiN films.The tensile samples with TiN films were mounted onthe tension attachment of CAMSCAN-40D scanningelectron microscope. Maximum loads of 220 N, 250 Nand 280 N were applied on Sample A, B and C,

172 N. Huang et al. / Surface and Coatings Technology 156 (2002) 170–175

Fig. 4. The TEM micrographs of a TiN film.(a) Bright field, 30 000=; (b) dark field, 24 000=; (c) selective area electron diffraction pattern;and(d) indexing.

respectively. The load increment was 20 N. The surfaceswere observed at 200–500= during loading and thedisplacement was recorded. The deformed surfaces ofthe tensile samples were also investigated at 500–3000= magnification. The final displacement of eachsample was measured using a micrometer.

3. Results and discussions

Fig. 2 is the morphology of the film surface obtained

by AFM. It shows that the surface is dense and theroughness is only several nanometers. The dimension ofthe hills at horizontal direction is approximately 20 nm.Fig. 3 is the composition profile of a PIIID TiN film ona silicon wafer obtained by the analysis of AES. Itshows that the distributions of Ti and N elements indepth are homogeneous, and the interlayer between theTiN film and silicon matrix is rather wide. The formationof chemical bonds of the film and matrix atoms is veryimportant to the binding of the film to the matrix.

173N. Huang et al. / Surface and Coatings Technology 156 (2002) 170–175

Table 2Indexing of the diffraction pattern of Fig. 4c

Diffraction Diameter of Substance Index fring diffraction rings identified crystalnumbers (mm) planes

1 20.0 TiN (111)2 23.4 TiN (200)3 34.8 TiN (311)4 39.6 TiN (222)5 46.2 TiN (400)6 51.0 TiN (420)

Fig. 5. The load–displacement curve of TiN-coated tensile Sample C.

Fig. 4 are TEM micrographs and selective area elec-tron diffraction patterns of the TiN film. Table 2 is theidentified index of diffraction pattern in Fig. 4c. Therings of the electron diffraction pattern indicate that theTiN film is composed of very small grains. Fig. 4b isthe dark field image of the film obtained using(311)diffraction, from which it is estimated that the grain sizeis approximately 40 nm.Fig. 5 is the load–displacement curve of Sample C.

The elastic deformation of the sample is approximatelyin the range from A to B. When the load increased overB, an obvious increase in displacement rate is detected.When the load is increased over point C, the displace-ment rate decreases again. In the range D–E, the loadis released gradually and the displacement decreasesalmost linearly. As the load was released completely,the elongation remained at approximately 0.16 mm. Theelongation is quite large from the neck area of thesample.Fig. 6 is SEM micrographs of the tensile Sample C,

which were taken in sequence to obtain an entire samplecross-section observation for Sample C, after the pullingexperiment. Some small flacks on the surface of theneck position of the sample are taken as referencepositions, shown as a–a, b–b, c–c, d–d, so that nopositions would be missed in the observation field. Nocrack or peeling are found on the surface. The sameresult was obtained from Sample A and B.Up to now, very few researches in this field have

studied the behavior of plastic deformation of TiN film.Kant and Sartwellw5x found that TiN film prepared byion beam assisted deposition has better mechanicalproperties than PVD TiN coatings through scratch andwear tests. They also carried out a thermal cycling testby annealing IBED-TiN coated AISI 52100 samples at850 8C for 15 min in ultrahigh vacuum. Although thedifference of thermal expansion coefficient of TiN andbearing steel could lead to larger thermal stress in thefilm, the film maintained intact. Therefore they declaredthat the TiN film deposition combined with ion beambombardment could result in ductile behavior. Thehigher density of the ion beam synthesized film and

wider film–substrate interlayer could be a reason forbetter ductility. We regard that besides the above reason,the TiN film we synthesized with the nano-grain struc-ture should be an important factor to the improvedmechanical behavior of the film, especially the abilityto withstand plastic deformation.In general, plastic deformation of a ceramic material

occurs only at high temperatures by grain boundaryslips and diffusions, which depends on the temperatureand grain size of the material. If the grain size isdecreased to nanometer scale, the large grain boundaryarea could produce the possibility of grain rotations andgrain boundary slipping at relative lower temperaturesand the material could undertake certain plastic defor-mation. This phenomenon has been proved for somebulk nano-grain ceramic materials such as CaFw6x and2

silicon nitride ceramicw7x, etc. For nano-grain structuredceramic films, the behavior of plastic deformation is notwell understood. Further investigations about mecha-nism of the plastic deformation of the coatings will bedone to understand it in more detail.

4. Conclusion

The titanium nitride film with nano-grain crystalstructure and wider film matrix interlayer is synthesizedusing the PIIID technique. No delaminating, peeling orcracking on the films have been found during tensionprocess. The film has the ability to withstand plasticdeformation to some extent.

Acknowledgments

This work was support by NSFC 39870199,G19990964706, 102-12-09-01, and Teacher Fund ofNational Education Committee of China, and joint sup-

174 N. Huang et al. / Surface and Coatings Technology 156 (2002) 170–175

Fig. 6. SEM micrographs of TiN-coated tensile Sample C after deformation.

ported by The Hong Kong Research Grants CommitteeCERG �9040498, Hong Kong RGC Germany JointScheme�9050150, and City University of Hong KongSRG�7001177.

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