Synthesis and mechanical properties of TiAlCxN1−x coatings deposited by arc ion plating

Surface & Coatings Technology 200 (2005) 1501 – 1506 www.elsevier.com/locate/surfcoat

Synthesis and mechanical properties of TiAlCx N1 deposited by arc ion plating

x

coatings

Chul Sik Jang a, Jun-Ha Jeon a, Pung Keun Song a, Myung Chang Kang b, Kwang Ho Kim a,* a

School of Materials Science and Engineering, Pusan National University, San30, Jangjeon-Dong, Keumjung, Busan 609-735, South Korea b School of Mechanical Engineering, ERC/NSDM, Pusan National University, Busan 609-735, South Korea Available online 9 September 2005

Abstract Quaternary TiAlCx N1 x coatings were deposited on steel substrates (SKD11) by arc ion plating (AIP) method using TiAl (Ti/Al atoms = 1) alloy target in CH4/(CH4 + N2) gaseous mixture. The carbon content of TiAlCx N1 x coatings was increased linearly with increasing CH4/(CH4 + N2) gas flow rate ratio. The microhardness of TiAlCx N1 x coatings increased from 22 GPa of (Ti,Al)N to 41 GPa of TiAlC0.48N0.52 coatings as the carbon content increased. The TiAlC0.48N0.52 coatings showed largely increased hardness with nearly maintaining the oxidation resistance of (Ti,Al)N coatings. The change of hardness with the carbon content had a relationship with the residual stress. In addition, the average friction coefficient of the TiAlCx N1 x coatings remarkably decreased with increasing carbon content. In this work, the microstructure and mechanical properties of the TiAlCx N1 x coatings were systematically investigated. D 2005 Elsevier B.V. All rights reserved. Keywords: Ti – Al – C – N; Arc ion plating; Microstructure; Wear resistance; Oxidation resistance

1. Introduction Ceramic coatings, transition metal nitrides and carbides have been widely used to various tools and dies for hard coating materials [1,2]. Among these coating systems, the (Ti,Al)N coatings have been extensively investigated because they showed the excellent oxidation behavior compared to that of TiN coatings even at over 800 -C [3,4]. In spite of the superior oxidation resistance of the coatings, the wear resistance of (Ti,Al)N coatings has been a considerable task [5]. It is still required to improve the mechanical properties of (Ti,Al)N coatings. On the other hand, Ti – C – N coatings showed high hardness, high corrosion resistance, and excellent wear resistance [6 – 10]. The properties of Ti– C –N coatings were, however, strongly dependent on the carbon and nitrogen contents in the coatings [11– 13]. Recently, TiAlCN coatings started to be investigated because of the mixed merits of superior oxidation * Corresponding author. Tel.: +82 51 510 2391; fax: +82 51 510 3660. E-mail address: [email protected] (K.H. Kim). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.08.065

behavior for (Ti,Al)N and excellent mechanical properties for Ti– C –N [14]. Up to now, TiAlCN coatings have been sparsely investigated, which have been focused on only a mechanical point of view [15 –17]. In this work, the microstructure, mechanical properties and oxidation behaviors of TiAlCx N1 x coatings were systematically investigated.

2. Experimental 2.1. Deposition of TiAlCx N1

x

coatings

TiAlCx N1 x coatings were deposited on steel substrates (SKD11) by an arc ion plating (AIP) technique using TiAl (50 at.% Ti and 50 at.% Al) alloy target at 300 -C with a bias voltage of 20 V. An arc cathode gun for TiAl source was installed on the chamber wall. Rotational substrate holder was located in the distance of 350 mm from target source. The substrates, which had been machined into disc type of 20 mm in diameter and 3 mm in thickness, were cleaned in an ultrasonic bath cleaner using both acetone

1502

C.S. Jang et al. / Surface & Coatings Technology 200 (2005) 1501 – 1506

x

coatings

The thickness and surface morphology of coatings were measured using a scanning electron microscope (SEM, Hitach, S-4200) and a stylus (a-STEP) instrument. Compositional analysis of the coatings to determine the Ti, Al, C, and N contents was carried out by electron probe microanalyzer (EPMA, Shimadzu, EPMA 1600). X-ray diffractometer (XRD, PHILIPS, X’Pert-MPD System) using CuKa radiation was used to identify the crystallinity of TiAlCx N1 x coatings. In order to observe the chemical bonding status of TiAlCx N1 x coatings, X-ray photoelectron spectroscopy (XPS, VG Scientifics, ESCALAB 250) was performed with monocromatized AlKa X-ray source. Microhardness of the coatings was evaluated using a microhardness tester with Knoop indenter (Matsuzawa, MMT-7) under a load of 25 g. Residual stress measurements were performed by means of sin2W method in a Philips Xray diffractometer equipped with CuKa line source. The average friction coefficient and wear behaviors were studied through sliding test using a conventional ball-on-disc wear apparatus. Steel balls (diameter 6.34 mm, 700 Hv0.2) were used as a counterpart material. The sliding tests were conducted with a sliding speed of 0.157 m/s under a load of 1 N at ambient temperature (approx. 22 -C) and relative humidity (25 – 30% RH) condition. The optical microscopy and scanning electron microscopy were carried out to observe the morphology of wear track after each sliding experiment. The wear track profiles were then measured by the stylus (a-STEP) instrument. For oxidation experiments of TiAlCx N1 x coatings, the coatings were placed on an alumina boat heated in a boxfurnace. Oxidation experiments were carried out at temperatures of 700 -C, 800 -C, and 900 -C for 60 min, respectively. To observe the oxidation behavior of the Table 1 Typical deposition conditions of TiAlCx N1 (AIP) Base pressure Working pressure CH4/(CH4 + N2) gas ratio Arc material Arc current Substrate temperature Substrate bias voltage Rotational velocity of substrate Typical coating thickness

x

Ti Al C N

60 50 40 30 20 10 0

coatings by arc ion plating 9.33  10 3 Pa 1.33  10 1 Pa 0¨1 TiAl (99.99%) 50 A 300 -C 20 V 25 rpm ¨2 Am

0.0

0.2

0.4

0.6

0.8

1.0

Gas volume ratio; CH4/(CH4+N2) [%] Fig. 1. Compositional changes in TiAlCx N1 x coatings as a function of CH4/(CH4+N2) gas ratio at a fixed TiAl arc current of 50 A.

coatings, XRD was performed to examine the oxide phase formation.

3. Results and discussion 3.1. Synthesis and characterization of TiAlCx N1

x

coatings

Fig. 1 shows the compositional changes of Ti, Al, C, and N elements in the TiAlCx N1 x coatings as a function of CH4/(CH4 + N2) gas ratio at a fixed TiAl arc current of 50 A. The carbon content in the TiAlCx N1 x coatings linearly increased from 0 to 47 at.% with increasing CH4/(CH4 + N2) gas ratio from 0 to 1, the reverse trend was seen for the nitrogen content. This result reflected that carbon and nitrogen contents in the TiAlCx N1 x coatings were successfully controlled by the variation of CH4/(CH4 + N2) gas ratio. Thus, we could prepare three kind of coatings as (Ti,Al)N, TiAlCx N1 x , and (Ti,Al)C coatings. Fig. 2 shows the X-ray diffraction patterns of TiAlCx N1 x coatings with various compositions (x = from

(Ti,Al)N (Ti,Al)N (111) (200)

Intensity [Arb. U.]

2.2. Characterization of TiAlCx N1

Content in coating [at. %]

and alcohol. Prior to deposition, the substrates were cleaned again by the ion bombardment using a bias voltage of 600 V under Ar atmosphere of 32 Pa for 10 min. The gas ratio of CH4/(CH4 + N2) was controlled in order to get various TiAlCx N1 x coatings at a constant arc current of 50 A. Typical deposition conditions for the TiAlCx N1 x coatings by our arc ion plating system are summarized in Table 1.

(Ti,Al)N (220)

(Ti,Al)N (Ti,Al)N (222) (311)

TiAlC TiAlC 0.67N0.33 TiAlC 0.48N0.52 TiAlC 0.37N0.63 TiAlC 0.15N0.85 TiAlN

30

40

50

60

70

80

Diffraction angle [2 theta] Fig. 2. X-ray diffraction patterns of TiAlCx N1 carbon contents.

x

coatings with various

C.S. Jang et al. / Surface & Coatings Technology 200 (2005) 1501 – 1506

(a) C 1s Al Kα

Intensity [Arb. U.]

281.5 eV TiC

TiAlC

TiAlC0.48 N0.52

TiAlC0.15 N0.85

TiAlN

288

286

284

282

280

278

Binding energy [eV]

(b)

N 1s Al Kα

396.9 eV Nitride

Intensity [Arb. U.]

0 to 1). The diffraction patterns of all coatings showed multiple orientations of (111), (200), (220), (311), and (222) of (Ti,Al)N crystal planes. These multiple orientations were in accordance with other (Ti,Al)N coatings [18 –21]. Any XRD peaks corresponding to Al and AlN were not observed. The diffraction peaks of (Ti,Al)N were gradually shifted toward lower 2h angle as the carbon content increased in the coatings. The gradual shift of peak position to lower 2h angles was mainly explained by two phenomena; the formation of solid solution by the incorporation of carbon atoms into (Ti,Al)N crystal lattice, and residual stress caused by differences in the thermal expansion between the substrate and the coatings [13]. Fig. 3 shows the interplanar distance, d 111, of TiN (111) crystal plane as a function of carbon content. The d 111 value continuously increased with increasing the carbon content. This result implied that carbon atoms were fully dissolved into the (Ti,Al)N crystal lattice where bigger carbon atoms in size were substituted for nitrogen atoms. In order to survey the bonding status with increasing carbon content in the coatings, X-ray photoelectron spectroscopy (XPS) was carried out for the TiAlCx N1 x coatings. Fig. 4 shows the XPS spectra near the binding energies of C and N for the TiAlCx N1 x coatings (x = 0, 0.15, 0.48, and 1). For the C 1s spectra in Fig. 4a, the peak at about 281.5 eV, which was corresponding to the formation of TiC, appeared with increasing the carbon content. For the N 1s spectra in Fig. 4b, the typical characteristics of nitride coatings (TiN and AlN) were shown with binding energy around 397 eV. The peak at around 397 eV corresponding to TiN and AlN [22,23] gradually disappeared with increasing the carbon content. From the instrumental analyses of XRD and XPS, it was found that the (Ti,Al)N coatings are gradually changed to (Ti,Al)C coatings with increasing the carbon content, and thus, have the transitive characteristics between (Ti,Al)N and (Ti,Al)C coatings by forming the substitutional solid solution replacing the carbon atoms for the nitrogen ones.

1503

TiAlC

TiAlC0.48 N0.52

TiAlC0.15N0.85

TiAlN

400

398

396

394

392

Binding energy [eV] Fig. 4. XPS spectra of (a) C 1s, and (b) N 1s for TiAlCx N1 various carbon contents.

3.2. Mechanical evaluation of TiAlCx N1

x

x

coatings

Fig. 5 shows the microhardness value and the residual stress of the TiAlCx N1 x coatings as a function of carbon content. As the carbon content in the coatings increased, 45

Microhardness [GPa]

d111 value [Å]

dTiN(111)JCPDF = 2.4400

2.44

2.42

0

40

-1

35 -2 30 -3

25

-4

20

2.40 0.0

0.2

0.4 .

0.6

0.8

1.0

Carbon content [x in TiAlCxN1-x] Fig. 3. Interplanar distance, d 111, of TiN (111) crystal plane with various carbon contents.

Residual stress [GPa]

2.46

coatings with

0.0

0.2

0.4

0.6

0.8

1.0

Carbon content [x in TiAlCxN1-x] Fig. 5. Variations of microhardness and residual stress of TiAlCx N1 coatings with various carbon contents.

x

1504

C.S. Jang et al. / Surface & Coatings Technology 200 (2005) 1501 – 1506

Friction coefficient

1.2 TiAlN

TiAlC0.48N0.52

1.0 0.8 0.6 0.4 0.2

TiAlC

0.0 0

5

10

15

20

25

30

+

Number of cycle [ 103] Fig. 6. Friction coefficients of (Ti,Al)N, TiAlC0.48N0.52, and (Ti,Al)C coatings against steel ball.

the microhardness of TiAlCx N1 x coatings drastically increased from 22 GPa of (Ti,Al)N coatings, and then reached a maximum value of approximately 41 GPa at

x = 0.48 in the TiAlCx N1 x coatings with the residual stress value of 4.2 GPa. Afterward, the microhardness gradually dropped to 29 GPa of (Ti,Al)C coatings with further increase of the carbon content beyond x = 0.48. The maximum hardness value (41 GPa) of TiAlC0.48N0.52 coatings was largely increased as one compared to that (22 GPa) of (Ti,Al)N coatings. The continuous increase of hardness with increase of carbon content can be explained due to the increase of covalent bonding characteristics with replacing the carbon atoms for nitrogen atoms, because the carbon atom has one less valency than that of nitrogen. For comparison, the hardness of TiCx N1 x coatings prepared by CVD method also increased monotonously with increase of the carbon content from x = 0 to 1, which could be explained by the increase of bond strength [24]. In case of the coatings prepared by CVD method, nearly stress-free coatings are obtained. However, in case of the coatings prepared by PVD method, the considerable amount of internal defects and residual stress is accumulated in the coatings [25 – 27]. The residual stress formed

(a)

2

0

Depth [µm]

4

Coating thickness

-2

300µm

0

200

400

600

Distance [µm]

800

(b) 2

0

Depth [µm]

4

Coating thickness

-2

300µm

0

200

400

600

800

Distance [µm]

(c) 2

0

Depth [µm]

4

Coating thickness

-2

30 µm 300

0

200

400

600

Distance [µm]

800

Fig. 7. Surface and cross-section morphologies of wear tracks for (a) (Ti,Al)N, (b) TiAlC0.48N0.52, and (c) (Ti,Al)C coatings after the sliding test of 30,000 cycles.

C.S. Jang et al. / Surface & Coatings Technology 200 (2005) 1501 – 1506

in our TiAlCx N1 x coatings was compressive which ranging from 1.1 to 4.2 GPa as shown in Fig. 5. The change of hardness with the carbon content in Fig. 5 can not be explained only with the bonding characteristics because the hardness continuously dropped again after x = 0.48. It has been reported that the hardening defect must be the most effective hardening mechanism in TiCx N1 x coatings prepared by PVD method [12]. The microstructural defects in the coatings can play as a barrier to dislocation propagation. The residual stress is, in general, related with the amount of defects in the coatings. In Fig. 5, the hardness was found to be in good trend with the absolute value of residual stress. For our TiAlCx N1 x coatings, the hardness value should be explained primarily with the defect hardening mechanism together with bonding characteristics. Fig. 6 shows the friction coefficients of (Ti,Al)N, TiAlC0.48N0.52, and (Ti,Al)C coatings against steel ball. The average friction coefficient of the coatings largely decreased from 0.8 of (Ti,Al)N to 0.38 of (Ti,Al)C with increasing the carbon content. This phenomenon seems to be caused by the formation of carbon rich transfer layer (or amorphous carbon layer), which acts as a solid lubricant to reduce direct contact between the coating surface and steel

1505

ball [6,11]. Fig. 7 shows SEM morphologies of wear track and the cross-section of (Ti,Al)N, TiAlC0.48N0.52, and (Ti,Al)C coatings after the sliding test of 30,000 cycles. As the carbon content in the coatings increased, the carbon rich transfer layer acted more effectively between the surface and steel ball. As a result, the morphologies of wear tracks got smoother, and the depth of wear tracks became shallower with the increase of carbon content as shown in Fig. 7. 3.3. Oxidation behavior of TiAlCx N1

x

coatings

Fig. 8 shows XRD patterns of (Ti,Al)N and TiAlC0.48 N0.52 coatings after oxidation at various temperatures from 700 -C to 900 -C. The TiO2 peaks of rutile crystal structure started to appear after oxidation at 800 -C in both coatings. Although the oxidation resistance of the (Ti,Al)N coatings was a little higher than that of the TiAlC0.48N0.52 coatings (comparing the XRD patterns at 800 -C in Fig. 8a and b), the TiAlC0.48N0.52 coatings still had fairly high oxidation resistance. This result indicated that the TiAlC0.48N0.52 coatings showed largely increased hardness with nearly maintaining the oxidation resistance of (Ti,Al)N coatings.

(a) (Ti,Al)N

Intensity [Arb. U.]

TiO2

(110)

800 °C

700 °C

Acknowledgements

900 °C

800 °C (220)

(111) (200)

(b)

Quaternary TiAlCx N1 x coatings were deposited on SKD11 substrates by an arc ion plating (AIP) technique. The chemical composition of TiAlCx N1 x coatings varied almost linearly with the CH4/(CH4+N2) gas ratio at constant arc current of 50 A and temperature of 300 -C. It could be suggested that quaternary TiAlCx N1 x coatings have transitive characteristics between (Ti,Al)N and (Ti,Al)C by replacing carbon for nitrogen. The hardness value of TiAlCx N1 x coatings steeply increased from 22 GPa of (Ti,Al)N coatings to 41 GPa. The highest hardness value of 41 GPa was obtained from the TiAlCx N1 x coatings containing carbon content of x = 0.48. The hardness value showed a relationship with the residual stress, and it was explained primarily with the hardening defect mechanism together with bonding characteristics. In addition, the average friction coefficient of the TiAlCx N1 x coatings remarkably decreased with increasing carbon contents. The TiAlC0.48N0.52 coatings showed largely increased hardness with nearly maintaining the oxidation resistance of (Ti,Al)N coatings.

(211)

(101) (111)

30

40

(311)

50

60

70

700 °C

80 TiAlC0.48 N0.52

Intensity [Arb. U.]

TiO2

(110)

(101) (111)

(211)

(301) 900 °C

(111)(200)

30

40

(220)

50

60

4. Conclusions

(311)

70

80

Diffraction angle [2 theta] Fig. 8. X-ray diffraction patterns of (a) (Ti,Al)N and (b) TiAlC0.48N0.52 coatings after oxidation at various temperatures from 700 -C to 900 -C.

This work was performed through NRL project supported by Ministry of Science and Technology of Korea (MOST). Authors also thank Dr. Won of Korea Basic Science Institute for obtaining and discussing XPS results.

1506

C.S. Jang et al. / Surface & Coatings Technology 200 (2005) 1501 – 1506

References [1] T. Cselle, A. Barimani, Surf. Coat. Technol. 76 – 77 (1995) 712. [2] U. Wiklund, M. Nordin, O. Wa¨nstrand, M. Larsson, Surf. Coat. Technol. 124 (2000) 154. [3] D. Mclntyre, J.E. Greene, G. Ha˚kansson, J.-E. Sundgen, W.-D. Mu¨nz, J. Appl. Phys. 67 (3) (1990) 1542. [4] S. PalDey, S.C. Deevi, Mater. Sci. Eng., A 342 (2003) 58. [5] S.-Y. Yoon, K.O. Lee, S.S. Kang, K.H. Kim, J. Mater. Process. Technol. 130 – 131 (2002) 260. [6] J.M. Larkner, W. Waldhauser, R. Ebner, Surf. Coat. Technol. 188 – 189 (2004) 519. [7] W. Precht, E. Lunarska, A. Czyzniewski, M. Pancielejko, W. Walkowiak, Vaccum 47 (6 – 8) (1996) 867. [8] J. Takadoum, H. Houmid-Bennani, D. Mairey, Z. Zsiga, J. Eur. Ceram. Soc. 17 (1997) 1929. [9] L.F. Senna, C.A. Achete, T. Hirsch, F.L. Freire Jr., Surf. Coat. Technol. 94 – 95 (1997) 390. [10] S.J. Bull, S.G. Bhat, M.H. Staia, Surf. Coat. Technol. 163 – 164 (2003) 507. [11] S.W. Huang, M.W. Ng, M. Samandi, M. Brandt, Wear 252 (2002) 566. [12] L. Karlsson, L. Hultman, J.-E. Sundgren, Thin Solid Films 371 (2000) 167. [13] L. Karlsson, L. Hultman, M.P. Johansson, J.-E. Sundgren, H. Ljungcrantz, Surf. Coat. Technol. 126 (2000) 1.

[14] O. Knotek, F. Lo¨ffler, L. Wolkers, Surf. Coat. Technol. 68 – 69 (1994) 176. [15] J.M. Lackner, W. Waldhauser, R. Ebner, R.J. Bakker, T. Scho¨berl, B. Major, Thin Solid Films 468 (1 – 2) (2004) 125. [16] J.M. Lackner, W. Waldhauser, E. Ebner, J. Kecke´s, T. Scho¨berl, Surf. Coat. Technol. 177 – 178 (2004) 447. [17] J.G. Han, K.H. Nam, I.S. Choi, Wear 214 (1998) 91. [18] J.Y. Rauch, C. Rousselot, N. Martin, Surf. Coat. Technol. 157 (2002) 138. [19] M.C. Kang, I.-W. Park, K.H. Kim, Surf. Coat. Technol. 163 – 164 (2003) 734. [20] M. Arndt, T. Kacsich, Surf. Coat. Technol. 163 – 164 (2003) 674. [21] A. Kimura, T. Murakami, K. Yamada, T. Suzuki, Thin Solid Films 382 (2001) 101. [22] P.W. Shum, Z.F. Zhou, K.Y. Li, Y.G. Shen, Mater. Sci. Eng., B 00 (2003) 1. [23] I. Berto´ti, Surf. Coat. Technol. 151 – 152 (2002) 194. [24] S. Veprek, M. Haussmann, S. Reiprich, L. Shizhi, J. Dian, Surf. Coat. Technol. 86 – 87 (1996) 394. [25] O. Knotek, R. Elsing, G. Kra¨mer, F. Jungblut, Surf. Coat. Technol. 46 (1991) 265. [26] H. Oettel, R. Wiedemann, S. Preißler, Surf. Coat. Technol. 74 – 75 (1995) 273. [27] I. Petrov, P. Losbichler, D. Bergstrom, J.E. Greene, W.-D. Mu¨nz, T. Hurkmans, Thin Solid Films 302 (1997) 179.