Deposition of (Ti,Cr,Zr)N-MoS2 Thin Films by

D.C. Magnetron SputteringSun Kyu Kim, Pham Van Vinh

School of Materials Science and Engineering, University of UlsanSan-29, Moogu-2 Dong, Nam-Gu

Ulsan 680-749, Korea

Abstract - As technology advances, there is a demand fordevelopment of hard, solid lubricant coating. (Ti,Cr,Zr)N-MoS2films were deposited on SKD11 tool steel substrate by co-deposition of MoS2 with (Ti,Cr,Zr)N using a D.C. magnetronsputtering process. The influence of the N2/Ar gas ratio, theamount of MoS2 in the films and the bias voltage on themechanical and structural properties of the films wereinvestigated.Keywords: solid lubricant coating, (Ti,Cr,Zr)N-MoS2 films,magnetron sputtering

I. INTRODUCTION

Development of new coatings have been undertakenactively to replace existing electroplated films and to increasethe durability of tools, dies and mechanical parts. Nitrides suchTiN, CrN, TiAlN have been studied a lot since the films havehigh hardness and wear resistance.Friction and wear degrades the function and the durability ofmachine parts. Liquid lubricants have been used to decreasethe wear of these operating parts. However, liquid lubricant isexpensive and pose an environmental concern for disposal.Solid lubricant such as MoS2 [1-4] has been exploited a lot toreplace the liquid lubricant. We can pursue two different waysto achieve hard solid lubricated coatings. One way is to deposita solid lubricated film on the hard films [5]. Another way is toincorporate a solid lubricant in a hard coating [6]. Carrera et al.[5] reported CrN/MoS2 coating. They deposited CrN film firstand MoS2 film was subsequently deposited. Incorporation ofMoS2 in a TiN matrix by D.C magnetron sputtering co-deposition has been studied by Gilmore et al. [6]. Kim andcoworkers reported incorporation of MoS2 in CrN matrix [7]and in a (TiCr)N matrix [8] by D.C magnetron sputtering.

II. EXPERIMENTAL DETAIL

The (Ti,Cr,Zr)N-MoS2 films were deposited on AISI H13tool steel (1.5%C, 11.5%oCr. 0.8%Mo, 0.9%oV) substrate by anunbalanced D.C. magnetron sputtering system. A schematicdiagram of the experimental apparatus is shown in Fig. 1. Onesputter source fitted with a titanium target (diameter of 12 mm)and the other with a MoS2 target (diameter of 76.2 mm) wereinstalled facing each other on each side of the chamber wall.On Ti target, six chromium pellets (diameter of 7 mm) and six

zirconium pellets (diameter of 7 mm) were attached alternately.A substrate holder, which could be rotated while applying biasvoltage was located at the center of the chamber. The distancefrom substrate to the Ti target and MoS2 were in turn 95 mmand 200 mm. The AISI H13 steel specimens were manuallyground and polished with 1500-grit SiC papers using a lowspeed polishing machine and degreased ultrasonically inalcohol. The base pressure achieved by a rotary pump and adiffusion pump before deposition was below 1.33xlO04Pa.Argon gas mixed with nitrogen gas at predetermined ratio wasintroduced to chamber to maintain working pressure. Beforedeposition, the substrate was plasma etched in argon pressureof 113.32 Pa for 40 min with current of 600 mA.

Fig. 1. Schematic diagram of the experimental apparatus.

To determine the effect of nitrogen partial pressure, the N2/Argas ratio of inlet gases was varied from 0.3 to 0.6. By varyingthe current ratio of MoS2 over TiCrZr, the influence of MoS2content of the film on the structural and mechanical propertiesof (Ti,Cr,Zr)N-MoS2 film was investigated.The phases and chemical composition of the films weredetermined by an X-ray diffractometer (Rigaku, RAD-3C) andan electron probe microanalyzer (EPMA-1400, Shimadzu).Morphology was observed by a field emission scanningmicroscope (JEOL, JSM-820). A computer-controllednanoindentor (MTS, Nanoindentor XP) equipped withBerkovich diamond indentor was used to measure the hardnessof the films. The continuous stiffness measurement methodwas employed.

1-4244-0427-4/06/$20.00 ©2006 IEEE - 190 - Oct. 18 -Oct. 20, 2006 FOST2006

III. RESULTS AND DISCUSSIONS

The hardness levels of the (Ti,Cr,Zr)N-MoS2 filmsdeposited at various N2/Ar gas ratios of inlet gases are shownin Fig. 2. The TiCrZr target current and the MoS2 target currentwere kept constant at 3.OOA and 0.25A, respectively. Althoughthe films did not exhibit high hardness in general, the highesthardness level was observed at the N2/Ar gas ratio of 0.3 andthe hardness decreases with the increase of the N2/Ar gas ratio.

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Fig. 2 Hardness of (Ti, Cr, Zr)N-MoS2 films deposited at various N2/Ar gasratios.

XRD diffractogram of these films are shown in Fig. 3. Mainpeak was TiN(1 11) and TiN(200), TiN(220), TiN(3 11) peakswere observed. There were not much noticeable differences.MoS2 content in the composite film was varied by applyingdifferent currents to the MoS2 target.

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-200 V. The hardness of these films was shown in Fig. 6.Hardness of the films increased with the increase of biasvoltage reaching 45 GPa at 150 V. Further, increase of biasvoltage decreased the hardness of the films.

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Cu rrent(mA)Fig. 5 EPMA analysis of (Ti, Cr, Zr)N-MoS2 films at various MoS2 currents.

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Fig. 3 XRD diffractograms of (Ti, Cr, Zr)N-MoS2 films deposited atvarious N2/Ar gas ratios

Hardness of the (Ti,Cr,Zr)N-MoS2 films deposited with variousMoS2 current is shown in Fig. 4. Hardness of the filmfluctuated between 8 GPa to 13 GPa. EPMA analysis of(Ti,Cr,Zr)N-MoS2 films doposited with various MoS2 currentsis shown in Fig. 5. Ti and Zr decrease whereas N, Mo and Sincreased with the increase of MoS2 current. (Ti,Cr,Zr)N-MoS2films were deposited with the change of the bias voltage up to

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[5] 5. Carrera. 0. Salas. J. J. Moore. A. Woolveraton. E. Suffer. Surf.Coat. Technol., 169 (2003) 25.[6] R. Gilmore, M.A. Baker, P.N. Gibson, W. Gissler, M. Stoiber, P.Lobicher, C. Mitterer, Surf. Coat. Technol., 108-109 (1998) 345.[7] S5K. Kim, B.C. Cha, Surf. Coat. Technol., 188-189 (2004) 174.[8] S5K. Kim, J.H. Kim, J. Kor. Inst. Surf. Eng. 39, 2 (2006) 70.

Fig. 7 Surface morphology of (Ti, Cr, Zr)N-MoS2 films at various biasvoltage.a) OV; b) -50V; c) -100V; d) -150V; e) -200V

Surface morphology of films deposited at various bias voltageswas shown in Fig. 7. Dome structure was not developedwithout applying bias voltage. Coarse dome structure wasdeveloped at -50 V. Dome structure became fine with theincrease of bias voltage resuilting in the increase of thehardness. At -200 V, dome structure collapsed exhibiting thedecrease of the hardness of the films.

IV. CONCLUSIONS

(Ti,Cr,Zr)N-MoS2 films deposited on SKD 11 tool steelusing unbalanced D.C. magnetron sputtering system. Thehighest hardness level was observed at the N2/Ar gas ratio of0.3. Hardness of the films did not change much with theincrease of the MoS2 content in the films. As the substrate biaspotential was increased, hardness level of the film increasedreaching a maximum value at -150 V and then decreased.Surface morphology of these films indicated that high hardnesswas attributed to the fine dome structure.

ACKNOWLEDGMENT

This work was supported by Grant No. R-m11-2000-086-0000-0 from the Center of Excellency Program of the KoreaScience Engineering Foundation and the Ministry of Scienceand Technology.

REFERENCES

[1]s. K. Kim, Y.H. Kim, K.H. Kim, Surf Coat. Technol., 169-170(2003) 428.[2] N.M. Renevier, J. Hampshire, V.C. Fox, J. Wits, T. Allen, D.GTeer, Surf. Coat. Technol., 142-144 (2001) 69.[3] X. Zhang, W. Lauwerens, J. He, J.-P. Cellis, J. Vac. Sci. Technol.,A21 (2) (2003) 416.[4] M.C. Simmons, A. Savans, E. Pflueger, H. Van Swygenhoven, Surf.Coat. Technol., 126 (2000) 15.

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