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Properties of TiN, ZrN and ZrTiN coatings prepared by cathodic arc evaporation
Materials Science and Engineering, A163 (1993) 211-214
211
Properties of TiN, ZrN and ZrTiN coatings prepared by cathodic arc evaporation J. Musil, I. St6pfinek, J. Musil, Jr., M. K o l e g a , O. Blfihovfi a n d J. Vysko~,il Institute of Technology and Reliability of Structures, Czechoslovak Academy of Sciences, Veleslavinova 11, 301 14 Pilsen (Czech Republic)
J. Kasl Central Research Institute, ~koda, Tylova 11, 316 O0 Pilsen (Czech Republic)
Abstract The paper is devoted to the reactive deposition of TiN, ZrN and ZrTiN coatings prepared by a cathodic arc ion-plating process. Cathodes made of Ti and Zr were evaporated in an N2 atmosphere. ZrTiN coatings were created by simultaneous evaporation of both Ti and Zr. Typical operation characteristics of individual depositions are presented. Special attention is devoted to the coating properties, namely to the film microstructure, surface morphology, phase and chemical composition, microhardness and adhesion.
I. Introduction
During the last few years, a rapid development of hard coatings has made it possible to use them in many industrial applications [1-3]. Recently, not only have the binary wear resistance coating systems such as TiN been improved, but complex multicomponent coatings are also being successfully developed using different physical vapour deposition (PVD) technologies [4--6]. The cathodic arc plasma deposition (CAPD) process is a convenient method for depositing multicomponent coatings. A principal advantage of the CAPD process is the fact that a significant amount of evaporated material is ionized (up to 80%-90%), and ion-assisted deposition of coatings can be realized. Ions fulfil several favourable functions and contribute significantly to enhanced film adhesion, production of a very dense microstructure, and also increased reactivity between gas and metal atoms [7, 8]. Until now, only a few papers on multicomponent coatings [5, 6, 9, 10] have been available. The present work deals with the study of the creation of TiN, ZrN and ZrTiN coatings by the CAPD process and compares the basic physical and mechanical properties of these coatings.
particle suppression) on polished, chemically, ultrasonically and ion cleaned high speed steel (HSS) substrates (4, 20x5 mm2). The coatings were deposited in a stainless steel deposition chamber (4, 600 mm) pumped down by an oil diffusion pump (2000 1 s -1) backed by a Roots pump (600 m 3 h -z) and rotary pump (30 m 3 h - l ) and equipped with three arc evaporators, see Fig. 1. Arc evaporators (4' 50 mm) with Ti and Zr targets were used. The experiments were carried out in nitrogen at pressure of 0.5 Pa. Typical deposition parameters are given in Table 1. The properties of coatings were determined by the following methods. They were analysed for the phase composition and lattice parameters by X-ray diffraction
._
gn
cotho0o
2. Experimental details
The TiN, ZrN and ZrTiN coatings were created by the conventional CAPD process (no means of macro-
Fig. 1. Schematic arrangement of substrate localization in the deposition chamber: position 1 for TiN, position 2 for ZrN and position 3 for ZrTiN.
Elsevier Sequoia
212
Z Musil et al. I TiN, ZrN, ZrTiN coatings TABLE 1. Deposition parameters of TiN, ZrN and ZrTiN coatings Coating
TiN
ZrN
ZrTiN
Working pressure p (Pa) Arc current of Zr cathode ID (A) Arc current of Ti cathode ID (A) Substrate bias voltage U, (V) Substrate temperature T~ (*C) Deposition angle a (deg) Deposition distance d (mm) Deposition rate av (/zm min -I)
0.5 100 -200 450 0 400 0.12
0.5 100 -200 460 0 400 0.16
0.5 100 100 -150 460--470 70 440 0.12
(a) TABLE 2. Mechanical properties of TiN, ZrN and ZrTiN coatings characterized by the scratch tester and microhardness measurements Coating h (~m)
TiN 4.6
ZrN 4.7
ZrTiN 4.5
L o (N) Lc2 (N) HV25 (kg mm -2)
36 39 2040-t-180
26 36 2050-1-150
28 43 2590-t-150
4./'
(b)
4.6
/
I!
4.5 0
4.4
~15 Z? I32! 2~k;V
xt,~ee IQ~t ~B3Sl
4.3
(c) 4.7: 0
/'/~
,/ / I
I
I
I
0,2
0.4
0.6
0.8
Zr (wI%)
Zr (~ */,)+Ti (wt%) Fig. 3. Lattice parameter a of nitride coatings as a function of element composition: curve 1, our experiment; curve 2, from ref. 11.
(d) Fig. 2. Typical characterization Of ZxTiN sample: (a) fracture cross-section, (b) surface topography, (c) EDAX map of Zr and (d) EDAX map of Ti.
(XRD) measurements in a Bragg-Brentano arrangement (DRON4), the surface morphology and fracture cross-section by scanning electron microscopy (SEM), (JEOL JSM840), the elements maps by energy-dispersive analysis of X-rays (EDAX, Link 860), the adhesive--cohesive strength by a scratch tester (AMI CSEM-Revetest), and the microhardness by a LECO tester (M400).
.I. Musil et al. / TiN, ZrN, ZrTiN coatings
213
T A B L E 3. Normal force F, (N) corresponding to different failure mechanisms of the coating and changes in acoustic emission signal and friction coefficient in the scratch test Coating h (/~m)
First "kidney-shaped" failure First cohesive flaking coating Lcl First exposure of the substrate Lc2 Sudden increase in A E signal Sudden increase in friction coefficient
TiN 1.5
4.6
-
28 27 51
(o)
(d)
(b}
(e)
(c)
ZrN
ZrTiN
1.7
4.7
1.6
4.5
37
23
36
-
26
19
28
26
-
39 35 67
53 52 54
36 26 74
41 18 47
28 43 28 61
(t)
Fig. 4. Typical scratch test pictures (300 × ) of TiN, Z r N and ZrTiN coatings at the same loading of diamond tip and two different thicknesses: (a) TiN, h = 1.5 p.m; (b) ZrN, h = 1.7 txm; (c) ZrTiN, h = 1.6 /xm; (d) TiN, h = 4.6 p.m; (e) ZrN, h = 4.7 #m; (f) ZrTiN, h = 4 . 5 /zm. T h e centre of the pictures corresponds to a normal force F , = 3 5 N. Scratch test conditions, d F , / d t = 100 N rain -1 and dx/dt=10 mm min-L
3. Results and discussion
3.1. Structural analysis The typical fracture cross-section and surface morphology of the ZrTiN coating (51 wt.%, Zr, 25 wt.% Ti) with macroparticle defects are shown in Figs. 2(a) and 2(b). Figures 2(c) and 2(d) show X-ray image micrographs of the distribution maps for Zr and Ti. The distribution of elements is homogeneous, and it
demonstrates that coevaporation of two materials can produce well mixed coatings. Figure 3 shows measurements of the lattice parameters a of the mixed f.c.c. ZrTiN structures. The increase in Zr content results in an increase in a and is accompanied by a shift of reflection angles in the XRD patterns towards smaller values, as is expected. Similar results for sputtered ZrTiN films were recently reported
[6].
214
J. Musil et al. / TiN, ZrN, ZrTiN coatings
3.2. Mechanical analysis Mechanical properties of the TiN, ZrN and ZrTiN coatings are summarized in Tables 2 and 3 and in Fig. 4. The results obtained show the following. (1) TiN and ZrN have the same microhardness, ZrTiN films have the highest microhardness. (2) TiN films with a thickness about 4.6 /~m have the highest resistance against cohesive failure compared with ZrTiN and ZrN. (3) The high brittleness of ZrN results in a very strong cohesive failure compared with cohesive failure for ZrTiN and TiN. (4) The highest value of critical force Lc2 is achieved for ZrTiN compared with both TiN and ZrN.
4. Conclusions
The paper shows that mixed ZrTiN coatings can be produced by coevaporation from two cathodes. Coatings containing both Ti and Zr exhibit some better properties compared with binary nitrides. One of the reasons for this is the full miscibility of Zr and Ti elements in the ZrTiN structure. Further study concentrated on optimization of the deposition process is now under way.
Acknowledgments This work was supported by a Grant-in-Aid GACSAV No. 11020 from the Czechoslovak Academy of Sciences. The authors would like to thank Drs. K. Stninsk~ for SEM analysis and V. Moty6ka for technical assistance in specimen preparation.
References 1 B. E. Jacobson and R. F. Bunshah, Thin Solid Films, 54 (1978) 107. 2 H. Randhawa, J. Vac. Sci. Technol. A, 4 (1986) 2755. 3 0 . Knotek, W. D. M~nz and T. Leyendecker, J. Vac. Sc£ Technol. A, 5 (4) (1987) 2173. 4 H. Holleck, Surf. Coat. Technol., 36 (1988) 151. 5 H. Freller and H. Haessler, Surf. Coat. Technol., 36 (1988) 219. 6 0 . Knotek, M. B6hmer, T. Leyendecker and F. Jungblut, Mater Sci. Eng., A 105-106 (1988) 481. 7 P.J. Martin, R. P. Netterfield, D. R. Me Kenzie, S. Falconer, C. G. Pacey, P. Thomas and W. G. Sainty, J. Vac. Sci. Technol. A, 5 (1) (1987) 22. 8 D.M. Sanders, D. B. Boercker and S. Falabeila, IEEE Trans. Plasma Sci., 18 (6) (1990) 883. 9 J. Aromaa, H. Ronkainen, A. Mahiout, S. P. Hannula, A. Leyland and A. Matthews, Mater. Sci. Eng., A 140 (1991) 722. 10 B. F. Coil, R. Fontana, A. Gates and P. Sathrum, Mater. Sci. Eng., A 140 (1991) 816. 11 W.B. Pearson, A Handbook of Lattice Spacings and Structures of Metals and Alloys, Pergamon, Oxford, 1958.
211
Properties of TiN, ZrN and ZrTiN coatings prepared by cathodic arc evaporation J. Musil, I. St6pfinek, J. Musil, Jr., M. K o l e g a , O. Blfihovfi a n d J. Vysko~,il Institute of Technology and Reliability of Structures, Czechoslovak Academy of Sciences, Veleslavinova 11, 301 14 Pilsen (Czech Republic)
J. Kasl Central Research Institute, ~koda, Tylova 11, 316 O0 Pilsen (Czech Republic)
Abstract The paper is devoted to the reactive deposition of TiN, ZrN and ZrTiN coatings prepared by a cathodic arc ion-plating process. Cathodes made of Ti and Zr were evaporated in an N2 atmosphere. ZrTiN coatings were created by simultaneous evaporation of both Ti and Zr. Typical operation characteristics of individual depositions are presented. Special attention is devoted to the coating properties, namely to the film microstructure, surface morphology, phase and chemical composition, microhardness and adhesion.
I. Introduction
During the last few years, a rapid development of hard coatings has made it possible to use them in many industrial applications [1-3]. Recently, not only have the binary wear resistance coating systems such as TiN been improved, but complex multicomponent coatings are also being successfully developed using different physical vapour deposition (PVD) technologies [4--6]. The cathodic arc plasma deposition (CAPD) process is a convenient method for depositing multicomponent coatings. A principal advantage of the CAPD process is the fact that a significant amount of evaporated material is ionized (up to 80%-90%), and ion-assisted deposition of coatings can be realized. Ions fulfil several favourable functions and contribute significantly to enhanced film adhesion, production of a very dense microstructure, and also increased reactivity between gas and metal atoms [7, 8]. Until now, only a few papers on multicomponent coatings [5, 6, 9, 10] have been available. The present work deals with the study of the creation of TiN, ZrN and ZrTiN coatings by the CAPD process and compares the basic physical and mechanical properties of these coatings.
particle suppression) on polished, chemically, ultrasonically and ion cleaned high speed steel (HSS) substrates (4, 20x5 mm2). The coatings were deposited in a stainless steel deposition chamber (4, 600 mm) pumped down by an oil diffusion pump (2000 1 s -1) backed by a Roots pump (600 m 3 h -z) and rotary pump (30 m 3 h - l ) and equipped with three arc evaporators, see Fig. 1. Arc evaporators (4' 50 mm) with Ti and Zr targets were used. The experiments were carried out in nitrogen at pressure of 0.5 Pa. Typical deposition parameters are given in Table 1. The properties of coatings were determined by the following methods. They were analysed for the phase composition and lattice parameters by X-ray diffraction
._
gn
cotho0o
2. Experimental details
The TiN, ZrN and ZrTiN coatings were created by the conventional CAPD process (no means of macro-
Fig. 1. Schematic arrangement of substrate localization in the deposition chamber: position 1 for TiN, position 2 for ZrN and position 3 for ZrTiN.
Elsevier Sequoia
212
Z Musil et al. I TiN, ZrN, ZrTiN coatings TABLE 1. Deposition parameters of TiN, ZrN and ZrTiN coatings Coating
TiN
ZrN
ZrTiN
Working pressure p (Pa) Arc current of Zr cathode ID (A) Arc current of Ti cathode ID (A) Substrate bias voltage U, (V) Substrate temperature T~ (*C) Deposition angle a (deg) Deposition distance d (mm) Deposition rate av (/zm min -I)
0.5 100 -200 450 0 400 0.12
0.5 100 -200 460 0 400 0.16
0.5 100 100 -150 460--470 70 440 0.12
(a) TABLE 2. Mechanical properties of TiN, ZrN and ZrTiN coatings characterized by the scratch tester and microhardness measurements Coating h (~m)
TiN 4.6
ZrN 4.7
ZrTiN 4.5
L o (N) Lc2 (N) HV25 (kg mm -2)
36 39 2040-t-180
26 36 2050-1-150
28 43 2590-t-150
4./'
(b)
4.6
/
I!
4.5 0
4.4
~15 Z? I32! 2~k;V
xt,~ee IQ~t ~B3Sl
4.3
(c) 4.7: 0
/'/~
,/ / I
I
I
I
0,2
0.4
0.6
0.8
Zr (wI%)
Zr (~ */,)+Ti (wt%) Fig. 3. Lattice parameter a of nitride coatings as a function of element composition: curve 1, our experiment; curve 2, from ref. 11.
(d) Fig. 2. Typical characterization Of ZxTiN sample: (a) fracture cross-section, (b) surface topography, (c) EDAX map of Zr and (d) EDAX map of Ti.
(XRD) measurements in a Bragg-Brentano arrangement (DRON4), the surface morphology and fracture cross-section by scanning electron microscopy (SEM), (JEOL JSM840), the elements maps by energy-dispersive analysis of X-rays (EDAX, Link 860), the adhesive--cohesive strength by a scratch tester (AMI CSEM-Revetest), and the microhardness by a LECO tester (M400).
.I. Musil et al. / TiN, ZrN, ZrTiN coatings
213
T A B L E 3. Normal force F, (N) corresponding to different failure mechanisms of the coating and changes in acoustic emission signal and friction coefficient in the scratch test Coating h (/~m)
First "kidney-shaped" failure First cohesive flaking coating Lcl First exposure of the substrate Lc2 Sudden increase in A E signal Sudden increase in friction coefficient
TiN 1.5
4.6
-
28 27 51
(o)
(d)
(b}
(e)
(c)
ZrN
ZrTiN
1.7
4.7
1.6
4.5
37
23
36
-
26
19
28
26
-
39 35 67
53 52 54
36 26 74
41 18 47
28 43 28 61
(t)
Fig. 4. Typical scratch test pictures (300 × ) of TiN, Z r N and ZrTiN coatings at the same loading of diamond tip and two different thicknesses: (a) TiN, h = 1.5 p.m; (b) ZrN, h = 1.7 txm; (c) ZrTiN, h = 1.6 /xm; (d) TiN, h = 4.6 p.m; (e) ZrN, h = 4.7 #m; (f) ZrTiN, h = 4 . 5 /zm. T h e centre of the pictures corresponds to a normal force F , = 3 5 N. Scratch test conditions, d F , / d t = 100 N rain -1 and dx/dt=10 mm min-L
3. Results and discussion
3.1. Structural analysis The typical fracture cross-section and surface morphology of the ZrTiN coating (51 wt.%, Zr, 25 wt.% Ti) with macroparticle defects are shown in Figs. 2(a) and 2(b). Figures 2(c) and 2(d) show X-ray image micrographs of the distribution maps for Zr and Ti. The distribution of elements is homogeneous, and it
demonstrates that coevaporation of two materials can produce well mixed coatings. Figure 3 shows measurements of the lattice parameters a of the mixed f.c.c. ZrTiN structures. The increase in Zr content results in an increase in a and is accompanied by a shift of reflection angles in the XRD patterns towards smaller values, as is expected. Similar results for sputtered ZrTiN films were recently reported
[6].
214
J. Musil et al. / TiN, ZrN, ZrTiN coatings
3.2. Mechanical analysis Mechanical properties of the TiN, ZrN and ZrTiN coatings are summarized in Tables 2 and 3 and in Fig. 4. The results obtained show the following. (1) TiN and ZrN have the same microhardness, ZrTiN films have the highest microhardness. (2) TiN films with a thickness about 4.6 /~m have the highest resistance against cohesive failure compared with ZrTiN and ZrN. (3) The high brittleness of ZrN results in a very strong cohesive failure compared with cohesive failure for ZrTiN and TiN. (4) The highest value of critical force Lc2 is achieved for ZrTiN compared with both TiN and ZrN.
4. Conclusions
The paper shows that mixed ZrTiN coatings can be produced by coevaporation from two cathodes. Coatings containing both Ti and Zr exhibit some better properties compared with binary nitrides. One of the reasons for this is the full miscibility of Zr and Ti elements in the ZrTiN structure. Further study concentrated on optimization of the deposition process is now under way.
Acknowledgments This work was supported by a Grant-in-Aid GACSAV No. 11020 from the Czechoslovak Academy of Sciences. The authors would like to thank Drs. K. Stninsk~ for SEM analysis and V. Moty6ka for technical assistance in specimen preparation.
References 1 B. E. Jacobson and R. F. Bunshah, Thin Solid Films, 54 (1978) 107. 2 H. Randhawa, J. Vac. Sci. Technol. A, 4 (1986) 2755. 3 0 . Knotek, W. D. M~nz and T. Leyendecker, J. Vac. Sc£ Technol. A, 5 (4) (1987) 2173. 4 H. Holleck, Surf. Coat. Technol., 36 (1988) 151. 5 H. Freller and H. Haessler, Surf. Coat. Technol., 36 (1988) 219. 6 0 . Knotek, M. B6hmer, T. Leyendecker and F. Jungblut, Mater Sci. Eng., A 105-106 (1988) 481. 7 P.J. Martin, R. P. Netterfield, D. R. Me Kenzie, S. Falconer, C. G. Pacey, P. Thomas and W. G. Sainty, J. Vac. Sci. Technol. A, 5 (1) (1987) 22. 8 D.M. Sanders, D. B. Boercker and S. Falabeila, IEEE Trans. Plasma Sci., 18 (6) (1990) 883. 9 J. Aromaa, H. Ronkainen, A. Mahiout, S. P. Hannula, A. Leyland and A. Matthews, Mater. Sci. Eng., A 140 (1991) 722. 10 B. F. Coil, R. Fontana, A. Gates and P. Sathrum, Mater. Sci. Eng., A 140 (1991) 816. 11 W.B. Pearson, A Handbook of Lattice Spacings and Structures of Metals and Alloys, Pergamon, Oxford, 1958.