Acta Polytechnica Vol. 43 No. l/2003 DLC Fitms Deposited by the DC PACVI) Method D. palamarchuk, M. zoriy,J. Gurovid, F.ierny, s. Konvidkov6,I. Htittel DLC (Dinmond,-Like carbon) coatings haue bee-n sugguted as protectiae surface layers.against .uear' Howeuer h"ard DLC coatings' especially those of greater ,hii,inru, hiae poor ad,hr1l.9.i7o substraies. We haae used' seieral iay to i'ncrease.the adhesion of DLC coatings brebared. by the pACVD (plasma Assisted. chemicar vapour Deposition) method in steel substrates. one of these is the DC PACVD method 'for' prepaing D LC flms. Keyu ords : D LC, PACVD, microhardne ss, adhesion' Electrode *ltt ruUto.t. Heating Subsffate Vacuum chamber I Introduction Diamond-like carbon (DLC) films have attracted consid- erable attention recently due to their properties of high mechanical hardness, high electrical resistivity, low friction coeflicient, optical transparency and chemical^inertness Il]' These properties make DI-C films suitable for numerous poterrtial applications in hard and wear-resistant coatings' iltfrog.upny, Protective optical and biomechanical coatings' electiolumines..n.. *uti,ials and held-emission devices [2' 3]. Various techniques have been used for preparing DLC fiim, including ion-beam deposition, reactive magnetron ,pr:ir..ing, pulsed laser deposition, a filtered cathodic vac- uum arc, dire.t.r.,r.e.,t plasma CVD, radio frequency plasma CVD and electron .yaio,.ott resonance microwave plasma cvD [4-7]. A problem that affects some of these methods is their poor adhesion to steel substrates with no intermediate layer' One fotential solution to this problem is to use current plasma for hepositing DLC films with no intermediate layer' This paper ,,.idi", th"e adhesion of DLC films to steel substrates and the microhardness of the laYer. 2 Experimental and results The DLC films were deposited with a direct current plasma assisted chemical vapor deposition process (DC i'nCvO) on silicon (lll) and iteel substrates' The steel sub- strate consists of 0.9 7o C, 4'14 7o Cr, 6'l Vo W' 5 Vo Mo' 2.02 VoY.These samples were polished up to a mirror finish' using a series of standard metallurgical polished steps' Befo.. p.epuration, the samples were, cleaned with ace- tone and isopropanollian in an ultrasonic bath' 'lhe apparatus for plasma assisted chemical vapor deposi- tion conslsts of a vacuum chamber, a diffusion pumP' two oarallel electrodes and a generator of DC PACVD plasma' i part of the PACVD apParatus is illustrated in Ftg'l' The DLC films were prepared on our substrates with the same parameters, aPart from the bias voltage' which was varied. This parameter was varied between -400 V and -900 V. Other processing parameters of the DLC layers' prepared with different uil.t.t of the bias voltage' are shown in Thble l. The thickness of the deposited DLC films was approxi- mately lpm, with diflerent values of bias voltage' Fig. l: Schematic view of DC PACVD aPParatus Table 1: Deposition Parameters of DLC films Then we investigated the dependence of microhardness o.r biu, voltage anithe adhesion of the DLC layers to the steel substrate. The microhardness of the substrates and substrates with DLC films was measured using a Leica DM Inverter Research Mi..or.op" for Materials Tesiing' The measurement results of microhardness for DLC layers prepared with the diflerent values of bias voltage are shown in Fig' 2' These graphs show the microhardness of the DLC layers' which incriases with increasing bias voltage' The photographs of the Vickers indentations clearly dem- onstrate the diilerence between layers with good and poor ad- hesion. The indentation in layers with poor adhesion to the substrate exhibits cracks in the diagonal direction' In the case of good adhesion no cracks are visible, and the layer remains .oitpu.t. This difference is shown in !ig' 3' 3.9.10-2 Torr3.9' l0-2 TorrInitial vacuum 7.1.10-l Torr7.1.10-l TorrPressure of CH, Bias current -400V+-900V-400V+-900V Thickness of DLC layer 27 Acta Polytechnica Vol. 43 No. l/2003 aaaa o G o 6 at oc P t! g .9 = 14 13 12 11 10 I 14 13 12 11 10 I I o G (9 o a(, E (! o .9 =400 500 700 Negative bias voltage [Vl *r Steel substrate {: Steel substrate with DLC laver 900 3UU Negative bias voltage [Vl * Silicon substrate {r Silicon substrate with DLC laver 700 Fig. 2: Dependence ofmicrohardness on bias voltage ofDLC layers on silicon and steel substrates Fig. 3: Shape ofVickers indentation in layerswith good and poor adhesion The microhardness of the coated materials is about l3 GPa higher than the base material at a load of 50 mN and bias voltage -900 V These coatings can be used for example for protecting metal bioimplants [8]. Acknowledgment This work was supported by a grant from the Grant Agen- cy of the Czech Republic 106/02/1 194 ,104/98:210000012 and CTU0204t 12. References ill Robertson, J.: Adv. Physics, Vol. 35, 1986, p. 317. tzl Lettington, A. H., Smith, C.: Diamond Relat. Mater., Vol. l. 1992. t3l Seth, J., Babu, S. V., Ralchenko, V. G.: Thin Solid Films, YoL254, 1995, p. 92. l4l Nagai, L, Ishitani, A., Kuroda, H.: Journal Appl. Phys., Vol.67, 1990, p.2890. t5l Harry, M., Zukotynski, S.: Journal Vac. Sci. Technol., A9, 1991, p.496. t6l Ganapathi, L., Giles, S., Rao, R.: Appl. Phys. Lett., Vol.63, 1993, p.993. t71 McKenzie, D. R., Miiller, D., Pailthorpe, B.A.: Phys. Rev. Lett., Vol. 67, 1991, p.773. i8l Konvickova, S., Valerian, D.: Acta Mechanica Slovaca, Vol.2, 1989, p.39. 28 Ing. Dmytro Palamarchuk e-mail : palamarc@student.fsid.cvut.cz Ing. Miroslav Zoriy Ing. Jdn Gurovii phone: +420 224 355 600 e-mail: gurovic@fsid.cvut.cz Doc. Ing. Franti5ek Cerny, CSc. phone: +420 224 352 437 e-mail : cernyf@fsid.cvut.cz f)epartment of Physics Doc. Ing. S. Konviikovd, CSc. phone: +420224352 5ll e-maii: konvicko@fsid.cvut.cz Department of Mechanics Czech Technical University in Prague Faculty of Mechanical Engineering Technick6 4 166 07 Prague 6, Czech Republic Doc. Ing. Ivan Htttel, CSc. phone: +420224353205 e-mail : huttel@vscht.cz Institute of Chemical Technology Technickii 3 166 28 Prague 6, Czech Republic 0aaa Scan 27 Scan 28