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Morphology and structure of ion-plated TiN, TiC and Ti(C, N) coatings
Thin Solid Films, I18 (1984) 243-254 METALLURGICAL
AND PROTECTIVE
MORPHOLOGY AND STRUCTURE Ti(C, N) COATINGS * H. M. GABRIEL?
243
COATINGS
OF ION-PLATED
TIN, TIC AND
AND K. H. KLOOS
Insritute of Material Science. Universily of Darmsradt (Received March 20.1984;
accepted
(F.R.G.)
April 12,1984)
Ion plating is now a well-established coating technique to produce hard and wear-resistant coatings. The coatings are influenced by many deposition parameters but also by the substrate to be coated. In this investigation the morphology and structure of different hard coatings are related to process and substrate parameters.
1.
INTRODUCTION
Ion- and plasma-assisted vacuum coating techniques for the deposition of hard and wear-resistant coatings for tribological applications have increased in importance’-5. One of the most recently developed processes is ion plating. Generally ion-plated coatings are well adherent and very dense. However, for the deposition of carbide and nitride coatings by a reactive process the ionization has to be enhanced to achieve a stoichiometric reaction between the vaporized material, e.g. titanium, and the reactive gases, e.g. N, or C2H, 6,7. The structure and morphology of deposited coatings depend on many process and substrate parameters. The coatings are mainly influenced by such deposition parameters as the substrate current density i,, the deposition rate r and the partial pressure pN2 or pCzH2 as well as by such substrate parameters as the structure and the surface roughness R,, R, or R,. 2.
EXPERIMENTAL
DETAILS
For the deposition of hard and wear-resistant coatings an evaporation unit is used which is modified for the ion plating process, i.e. the 10 kW electron beam gun is differentially pumped. This system is used in the diode mode and is completed with a thermionically assisted triode to enhance the ionization. This system is similar to that reported in ref. 7. It is estimated that up to 10% of the particles (evaporated material, reactive and * Paper presented April 9-13, 1984. t Present address:
0040-6090/84/$3.00
at the International
Conference
on Metallurgical
Multi Arc G.m.b.H.,
4000 Diisseldorf,
Coatings,
San Diego, CA, U.S.A.,
F.R.G.
0 Elsevier Sequoia/Printed
in The Netherlands
244
H. M. GABRIEL.
K. H. KLOOS
process gases) are ionized and this high degree of ionization supports the reaction between the vaporized material and the reactive gases. Even at high deposition rates stoichiometric coatings can be produced as shown for TIN (Fig. 1). In this investigation thin coatings of TIN, TIC and Ti(C, N) were deposited onto hardened ball-bearing steel (En 31) substrates. The process parameters, namely the substrate current density (0.4-1.5 mA cm-‘), the deposition rate (100-500 8, s-l) and the partial pressure pN2or pCIH2of reactive gases, were changed systematically.
II’ 0
Fig. 1. Chemical
100 composition
MO of ion-plated
The substrates to be coated nesses were as follows :
300
4w
deposItIon rate l~isl
TiN compounds
had different
(LJ5= 1 kV; i, = 1.0 mA cm- ‘). surface finishes. The surface rough-
R, = 0.330 urn
R, = 0.040 urn
R, = 0.180 urn
(polished)
R, = 1.650 urn
R, = 0.175 urn
R, = 0.850 urn
(lapped)
R, = 4.100 urn
R, = 0.550 urn
R, = 2.550 urn
(ground)
Scanning electron micrographs were taken from fracture cross sections produced by impact tests to reveal the morphology of the deposited coatings. The structure and composition of the coatings were examined by X-ray diffraction investigations. 3. RESULTS AND DISCUSSION Figure 2 shows fracture cross sections of substoichiometric TIN, coatings deposited at high substrate voltages and pressures in the diode mode. With decreasing deposition rate and increasing substrate current density the coatings become more compact and their density increases. The adhesion is not perfect despite the use of very thin titanium underlayers. The chemical composition of the coatings is not stoichiometric because of insufficient reaction between the evaporated titanium and the reactive gas N,. x varies between 0.5 and 0.7 and increases with increasing current density and decreasing deposition rate. Generally, the structure, the adhesion and the chemical composition of TIN coating produced by diode ion plating are inadequate in many
ION-PLATED
TiN,TiC
AND
Ti(C,N)
COATINGS
245
(a)
W
(4 Fig. 2. Fracture cross sections of ion-plated TIN, (x = 0.5-0.7) coatings obtained at various deposition rates r and substrate current densities i, (diode ion plating; US = 5 kV; prnt = 6 x lo-’ mbar; polished substrates):(a)r=2OOAs-‘,iS=0.4mAcm-*;(b)r= 1508,~-~,i,=O.5mAcm-~;(c)r= 120As-‘, i, = 0.6 mA cm-‘.
246
H. M. GABRIEL,
K. H. KLOOS
ways. Only at deposition rates between 20 and 50 8, s -’ can wear-resistant TIN coatings be produced by diode ion plating3. To improve the properties of the coatings there is obviously a necessity for ionization enhancement to obtain denser, more adherent and stoichiometric coatings. A thermionically assisted triode was incorporated in the system to establish an intensified glow discharge in the 10e3 mbar pressure range at low substrate voltages. The substrate current densities were increased to 1.5 mA cm-’ considering the annealing behaviour of the substrate material made from ball-bearing steel (65 _+ 1 HRC). Figure 3 shows fracture cross sections of stoichiometric TIN films deposited in the triode mode. With increasing substrate current densities a grain refinement was observed and the topography became smoother. This is related to the increased number of lattice defects in the near-surface region created by the enhanced ion bombardment, so that an increased number of growing columns is created. The coatings deposited at low current densities had a (111) preferred orientation while at higher current densities they exhibited a (200) texture. This has also been confirmed by other researchers’. The hardness of all the coatings shown in Fig. 3 is about 2100 HV 0.015. The adhesion of the coatings is shown to be excellent by the fact that they are not removed by the impact test. This was also confirmed by tribological tests’. The partial pressures of the reactive gases also exert a powerful influence on the morphology and grain structure of the coatings. With increasing N, partial pressure a grain coarsening was observed (Fig. 4) and at significant higher pressures loosely bonded powdery coatings were deposited. With increasing pN2the substrate current density has to be increased to obtain a higher resputtering of the deposited coating to suppress a coarse grain structure. The TIN and &-Ti,N phases are evident in the coating presented in Fig. 4(a) while the other coatings (Figs. 4(b) and 4(c)) consist of TIN. The preferred orientation of all the coatings is (200). The hardness of the TIN coatings is about 2100 HV 0.015. The coating with the small amount of the E phase showed a hardness of 2400 HV 0.015. Furthermore, the morphology and grain structure of the coatings are influenced by the deposition rate. Irrespective of the substrate current density, for the TiN coatings a significant densification in connection with a grain refinement was observed with increasing deposition rate (Fig. 5). The texture of the coatings changed from (200) at low deposition rates to (111) at higher deposition rates. Even at the highest deposition rate (500 A s-‘) used in this investigation the preferred orientation is (111). This clearly indicates that the texture is influenced by the substrate current density and the deposition rate. The coating shown in Fig. 5(b) is that with the highest hardness of 2750-3150 HV 0.015 as a result of the considerable amount of the E-Ti,N phase in it, as can be seen from Fig. 1. The adhesion of the coatings is excellent. However, the coatings are influenced not only by the deposition parameters but also by the structure of the substrate3 and the substrate topography. The lower the roughness of the substrate the smaller is the grain size as is shown in Fig. 6 for TiN and in Fig. 7 for TiC coatings. This is again related to the significantly higher number of defects on a polished surface created by the intense ion bombardment”. Moreover, on polished substrates the growing columns do not influence each other
ION-PLATED
247
TIN, TIC AND Ti(C,N) COATINGS
(4
(‘4
(4 Fig. 3. Fracture cross sections of ion-plated TiN coatings at various substrate current densities i, (thermionically assisted triode ion plating; US = 1 kV; ptet= 5.6 x 10m3 mbar; r = 100 A s-l; polished substrates):
(a) i, = 0.7 mA cmF2; (b) i, = 1.1 mA cm-‘;
(c) i, = 1.5 mA cm-2.
248
H. M. GABRIEL,
K. H. KLOOS
(a)
UN
(cl Fig 4. Fracture cross sections of ion-plated TiN, coatings at various N, partial pressures pNI (thermionically assisted triode ion plating; Us = 1 kV; pAr = 5 x 10e3 mbar; 6 = 1.1 mA cm-‘; r = 100 W s-1; ground substrates): (a) pN2 = 0.2 x 1W3 mbar; (b) pN2 = 0.6 x 10m3 mtw (C) PN = 1.0~ 10-j mbar.
ION-PLATED
TiN,TiC
AND
Ti(C,N)
COATINGS
249
(4
(b) Fig. 5. Fracture cross sections of ion-plated TiN coatings at various deposition rates r (thermionically assisted triode ion plating; US = 1 kV; i, = 1.1 mA cm-*; polished substrates): (a) r = 100 8, s-l, = 3OOAs-‘,p,,, = 6x 10e3mbar. Pm1 = 5.6x 10e3mbar;(b)r
while on lapped and ground surfaces because of the higher roughness the columns grow at different angles according to the topography. In general, the probability of a “cauliflower” structure increases with increasing surface roughness and there are only slight possibilities of preventing such structures by increasing the current density, decreasing the total pressure or adjusting the deposition rate. The TiN coatings shown in Fig. 6 exhibit a (200) preferred orientation while the TIC coatings (Fig. 7) show a strong (111) orientation. The hardness of the deposited TiN coatings (Fig. 6) is about 2100 HV 0.015. The TiC coatings (Fig. 7) are slightly weaker (1800 HV 0.015). The adhesion of all the coatings is good. As shown for TiN coatings the grain structure was densified with increasing deposition rate. TIC coatings, however, exhibit a coarser grain structure with increasing deposition rate (Fig. 8). The diameters of the single columns increase with the deposition rate, and the surface topography becomes slightly rougher. To form a refined grain structure such as those shown for the TiN coatings, TIC
250
H. M. GABRIEL,
K. H. KLOOS
(4
W
(4 Fig. 6. Fracture cross sections of ion-plated TIN coatings on substrates of different surface roughness (thermionically assisted triode ion plating; US = 1 kV; p,., = 5.6 x 10m3 mbar; i, = 1.5 mA cm-‘; r = 100 8, s-l): (a) polished substrate;(b) lapped substrate;(c) ground substrate.
ION-PLATED
TiN,TiC
AND
Ti(C,N)
COATINGS
251
Fig. 7. Fracture cross sections of ion-plated TiC coatings on substrates of different surface roughness (thermionically assisted triode ion plating; US = 1 kV; pAr = 5 x 10m3 mbar; i, = 0.9 mA cm-*; r = 300 A s-l): (a) polished substrate;(b) ground substrate.
coatings require significantly higher substrate current densities. All TiC coatings shown in Fig. 8 have a (111) preferred orientation. This orientation becomes stronger with increasing deposition rate. The hardness also increases up to 2720 HV 0.015 for the coatings with the strongest orientation (Fig. 8(c)). Both the strong (111) orientation and the high hardness are advantageous properties for tribological applications. The adhesion of all the coatings is perfect. Ion-plated Ti(C,N) coatings show an increasingly fibrous grain structure at increasing deposition rates (Fig. 9) with significantly unidirectional columns perpendicular to the substrate surface at high rates. The grain structure is influenced by the partial pressures, the substrate current density and the surface roughness similarly to TIN. All deposited coatings contain a certain amount of the s-Ti,N phase, which increases with increasing deposition rate. At low rates the TiN content is higher than that of TiC and vice versa at high rates. Hardnesses of up to 2150 HV 0.015 were obtained for Ti(C, N) coatings at a deposition rate of 300 A s-l. At higher rates the hardness decreased below 2000 HV 0.015.
252
H. M. GABRIEL,
K. H. KLOOS
(4
W
Fig. 8. Fracture cross sections of ion-plated TiC coatings at various deposition rates r (thermionically assisted triodeionplating; U, = 1 kV; pAr = 5 x lo-’ mbar; i, = 1.1 mAcm_‘; polished substrates): (a) r=
120.&s-‘;(b)r
= 3OOAs-‘;(c)r
= 5OOAs-‘.
ION-PLATED
TIN, TiC AND Ti(C,N) COATINGS
253
(4
(b)
Fig.‘9. Fracture cross sections of ion-plated Ti(C,N) coatings at various deposition rates r (thermionically assisted triode ion plating; U, = 1 kV; pAr = 5 x 1O-3 mbar; i, = 1 mA cm-*; polished substrates): (a)r = 150As-‘;(b)r= 3OOAs-‘;(c)r = TOOAs-‘.
254 4.
H. M. GABRIEL,
SUMMARIZING
K. H. KLOOS
REMARKS
This investigation clearly shows that the morphology, the grain structure, the stoichiometry and the texture of hard and wear-resistant carbide and nitride coatings produced by reactive ion plating are strongly influenced by the process parameters (substrate current density, partial pressures of the reactive gases and deposition rate) and by the substrate roughness. To form dense coatings it is necessary to enhance the ionization as was achieved with a thermionically assisted triode. With increasing current density the coatings become more compact and the adhesion is improved. The deposition rate influences the grain structure depending on the material to be deposited but also the orientation of the coating. The reactive gas partial pressures have to be correctly balanced with respect to the deposition rate to attain the correct stoichiometry as well as to obtain a dense grain structure. Stoichiometric coatings were produced over a very wide range of deposition rates. This investigation showed that hard wear-resistant coatings such as the carbides and nitrides of titanium can be produced by ion plating with a wide range of properties, i.e. morphology, structure and composition, according to their application4v9. ACKNOWLEDGMENT
The author wishes to thank the Deutsche Forschungsgemeinschaft (DFG) for their financial support. This paper is a contribution of the Sonderforschungsbereich 152 “Oberflachentechnik” of the DFG. This work is part of the Dr.-Ing. dissertation of H. M. Gabriel at the University of Darmstadt. REFERENCES 1 2 3 4 5 6 7 8 9 10
R. L. Hatschek, Coatings: revolution in HSS tools, Am. Mach., (March 1983) 129-144. K. Giihring and W. Kerschl, Hartstofibeschichtete Schneidwerkzeuge, Schneidwerkzeuge aus Schnellarbeitsstahl, Ind.-Anz., 102 (100) (1980) 12. K. H. Kloos, E. Broszeit, H. M. Gabriel and H. J. Schriider, Thin TiN coatings deposited onto nodular cast iron by ion- and plasma-assisted coating techniques, Thin Solid Films, 96 (1982) 67-77. H. M. Gabriel, F. Schmidt, E. Broszeit and K. H. Kloos, Improved component performance of vane pumps by ion-plated TIN coatings, Thin Solid Films, 108 (1983) 189. A. Matthews and D. G. Teer, Ion plated TIN coatings for dies and moulds, Proc. Int. Co& on Ion Plating and Allied Techniques, London, July 1979, CEP Consultants, Edinburgh, 1979, pp. 225-229. K. H. Kloos, E. Broszeit and H. M. Gabriel, Moglichkeiten der Ionisierungserhiihung beim Ion Plating Verfahren, Vuk.-Tech., 30 (1) (1981) 15-21. A. Matthews and D. G. Teer, Characteristics of a thermionically assisted triode ion plating system, Thin Solid Films, 80 (1981) 41-48. A. Matthews and D. G. Teer, Deposition of Ti-N compounds by thermionically assisted triode reactive ion plating, Thin Solid Films, 72 (1980) 541-549. K. H. Kloos, E. Broszeit, H. M. Gabriel and H. J. Schroder, Wear behaviour of hard coated cast iron, Wissenschaft und Technik, Vol. 20, University of Darmstadt, Darmstadt, 1983. H. M. Gabriel, Influence of ion bombardment on the substrate material, e.g. hardened ball-bearing steel En 31, Vuk.-Tech., to be published.
AND PROTECTIVE
MORPHOLOGY AND STRUCTURE Ti(C, N) COATINGS * H. M. GABRIEL?
243
COATINGS
OF ION-PLATED
TIN, TIC AND
AND K. H. KLOOS
Insritute of Material Science. Universily of Darmsradt (Received March 20.1984;
accepted
(F.R.G.)
April 12,1984)
Ion plating is now a well-established coating technique to produce hard and wear-resistant coatings. The coatings are influenced by many deposition parameters but also by the substrate to be coated. In this investigation the morphology and structure of different hard coatings are related to process and substrate parameters.
1.
INTRODUCTION
Ion- and plasma-assisted vacuum coating techniques for the deposition of hard and wear-resistant coatings for tribological applications have increased in importance’-5. One of the most recently developed processes is ion plating. Generally ion-plated coatings are well adherent and very dense. However, for the deposition of carbide and nitride coatings by a reactive process the ionization has to be enhanced to achieve a stoichiometric reaction between the vaporized material, e.g. titanium, and the reactive gases, e.g. N, or C2H, 6,7. The structure and morphology of deposited coatings depend on many process and substrate parameters. The coatings are mainly influenced by such deposition parameters as the substrate current density i,, the deposition rate r and the partial pressure pN2 or pCzH2 as well as by such substrate parameters as the structure and the surface roughness R,, R, or R,. 2.
EXPERIMENTAL
DETAILS
For the deposition of hard and wear-resistant coatings an evaporation unit is used which is modified for the ion plating process, i.e. the 10 kW electron beam gun is differentially pumped. This system is used in the diode mode and is completed with a thermionically assisted triode to enhance the ionization. This system is similar to that reported in ref. 7. It is estimated that up to 10% of the particles (evaporated material, reactive and * Paper presented April 9-13, 1984. t Present address:
0040-6090/84/$3.00
at the International
Conference
on Metallurgical
Multi Arc G.m.b.H.,
4000 Diisseldorf,
Coatings,
San Diego, CA, U.S.A.,
F.R.G.
0 Elsevier Sequoia/Printed
in The Netherlands
244
H. M. GABRIEL.
K. H. KLOOS
process gases) are ionized and this high degree of ionization supports the reaction between the vaporized material and the reactive gases. Even at high deposition rates stoichiometric coatings can be produced as shown for TIN (Fig. 1). In this investigation thin coatings of TIN, TIC and Ti(C, N) were deposited onto hardened ball-bearing steel (En 31) substrates. The process parameters, namely the substrate current density (0.4-1.5 mA cm-‘), the deposition rate (100-500 8, s-l) and the partial pressure pN2or pCIH2of reactive gases, were changed systematically.
II’ 0
Fig. 1. Chemical
100 composition
MO of ion-plated
The substrates to be coated nesses were as follows :
300
4w
deposItIon rate l~isl
TiN compounds
had different
(LJ5= 1 kV; i, = 1.0 mA cm- ‘). surface finishes. The surface rough-
R, = 0.330 urn
R, = 0.040 urn
R, = 0.180 urn
(polished)
R, = 1.650 urn
R, = 0.175 urn
R, = 0.850 urn
(lapped)
R, = 4.100 urn
R, = 0.550 urn
R, = 2.550 urn
(ground)
Scanning electron micrographs were taken from fracture cross sections produced by impact tests to reveal the morphology of the deposited coatings. The structure and composition of the coatings were examined by X-ray diffraction investigations. 3. RESULTS AND DISCUSSION Figure 2 shows fracture cross sections of substoichiometric TIN, coatings deposited at high substrate voltages and pressures in the diode mode. With decreasing deposition rate and increasing substrate current density the coatings become more compact and their density increases. The adhesion is not perfect despite the use of very thin titanium underlayers. The chemical composition of the coatings is not stoichiometric because of insufficient reaction between the evaporated titanium and the reactive gas N,. x varies between 0.5 and 0.7 and increases with increasing current density and decreasing deposition rate. Generally, the structure, the adhesion and the chemical composition of TIN coating produced by diode ion plating are inadequate in many
ION-PLATED
TiN,TiC
AND
Ti(C,N)
COATINGS
245
(a)
W
(4 Fig. 2. Fracture cross sections of ion-plated TIN, (x = 0.5-0.7) coatings obtained at various deposition rates r and substrate current densities i, (diode ion plating; US = 5 kV; prnt = 6 x lo-’ mbar; polished substrates):(a)r=2OOAs-‘,iS=0.4mAcm-*;(b)r= 1508,~-~,i,=O.5mAcm-~;(c)r= 120As-‘, i, = 0.6 mA cm-‘.
246
H. M. GABRIEL,
K. H. KLOOS
ways. Only at deposition rates between 20 and 50 8, s -’ can wear-resistant TIN coatings be produced by diode ion plating3. To improve the properties of the coatings there is obviously a necessity for ionization enhancement to obtain denser, more adherent and stoichiometric coatings. A thermionically assisted triode was incorporated in the system to establish an intensified glow discharge in the 10e3 mbar pressure range at low substrate voltages. The substrate current densities were increased to 1.5 mA cm-’ considering the annealing behaviour of the substrate material made from ball-bearing steel (65 _+ 1 HRC). Figure 3 shows fracture cross sections of stoichiometric TIN films deposited in the triode mode. With increasing substrate current densities a grain refinement was observed and the topography became smoother. This is related to the increased number of lattice defects in the near-surface region created by the enhanced ion bombardment, so that an increased number of growing columns is created. The coatings deposited at low current densities had a (111) preferred orientation while at higher current densities they exhibited a (200) texture. This has also been confirmed by other researchers’. The hardness of all the coatings shown in Fig. 3 is about 2100 HV 0.015. The adhesion of the coatings is shown to be excellent by the fact that they are not removed by the impact test. This was also confirmed by tribological tests’. The partial pressures of the reactive gases also exert a powerful influence on the morphology and grain structure of the coatings. With increasing N, partial pressure a grain coarsening was observed (Fig. 4) and at significant higher pressures loosely bonded powdery coatings were deposited. With increasing pN2the substrate current density has to be increased to obtain a higher resputtering of the deposited coating to suppress a coarse grain structure. The TIN and &-Ti,N phases are evident in the coating presented in Fig. 4(a) while the other coatings (Figs. 4(b) and 4(c)) consist of TIN. The preferred orientation of all the coatings is (200). The hardness of the TIN coatings is about 2100 HV 0.015. The coating with the small amount of the E phase showed a hardness of 2400 HV 0.015. Furthermore, the morphology and grain structure of the coatings are influenced by the deposition rate. Irrespective of the substrate current density, for the TiN coatings a significant densification in connection with a grain refinement was observed with increasing deposition rate (Fig. 5). The texture of the coatings changed from (200) at low deposition rates to (111) at higher deposition rates. Even at the highest deposition rate (500 A s-‘) used in this investigation the preferred orientation is (111). This clearly indicates that the texture is influenced by the substrate current density and the deposition rate. The coating shown in Fig. 5(b) is that with the highest hardness of 2750-3150 HV 0.015 as a result of the considerable amount of the E-Ti,N phase in it, as can be seen from Fig. 1. The adhesion of the coatings is excellent. However, the coatings are influenced not only by the deposition parameters but also by the structure of the substrate3 and the substrate topography. The lower the roughness of the substrate the smaller is the grain size as is shown in Fig. 6 for TiN and in Fig. 7 for TiC coatings. This is again related to the significantly higher number of defects on a polished surface created by the intense ion bombardment”. Moreover, on polished substrates the growing columns do not influence each other
ION-PLATED
247
TIN, TIC AND Ti(C,N) COATINGS
(4
(‘4
(4 Fig. 3. Fracture cross sections of ion-plated TiN coatings at various substrate current densities i, (thermionically assisted triode ion plating; US = 1 kV; ptet= 5.6 x 10m3 mbar; r = 100 A s-l; polished substrates):
(a) i, = 0.7 mA cmF2; (b) i, = 1.1 mA cm-‘;
(c) i, = 1.5 mA cm-2.
248
H. M. GABRIEL,
K. H. KLOOS
(a)
UN
(cl Fig 4. Fracture cross sections of ion-plated TiN, coatings at various N, partial pressures pNI (thermionically assisted triode ion plating; Us = 1 kV; pAr = 5 x 10e3 mbar; 6 = 1.1 mA cm-‘; r = 100 W s-1; ground substrates): (a) pN2 = 0.2 x 1W3 mbar; (b) pN2 = 0.6 x 10m3 mtw (C) PN = 1.0~ 10-j mbar.
ION-PLATED
TiN,TiC
AND
Ti(C,N)
COATINGS
249
(4
(b) Fig. 5. Fracture cross sections of ion-plated TiN coatings at various deposition rates r (thermionically assisted triode ion plating; US = 1 kV; i, = 1.1 mA cm-*; polished substrates): (a) r = 100 8, s-l, = 3OOAs-‘,p,,, = 6x 10e3mbar. Pm1 = 5.6x 10e3mbar;(b)r
while on lapped and ground surfaces because of the higher roughness the columns grow at different angles according to the topography. In general, the probability of a “cauliflower” structure increases with increasing surface roughness and there are only slight possibilities of preventing such structures by increasing the current density, decreasing the total pressure or adjusting the deposition rate. The TiN coatings shown in Fig. 6 exhibit a (200) preferred orientation while the TIC coatings (Fig. 7) show a strong (111) orientation. The hardness of the deposited TiN coatings (Fig. 6) is about 2100 HV 0.015. The TiC coatings (Fig. 7) are slightly weaker (1800 HV 0.015). The adhesion of all the coatings is good. As shown for TiN coatings the grain structure was densified with increasing deposition rate. TIC coatings, however, exhibit a coarser grain structure with increasing deposition rate (Fig. 8). The diameters of the single columns increase with the deposition rate, and the surface topography becomes slightly rougher. To form a refined grain structure such as those shown for the TiN coatings, TIC
250
H. M. GABRIEL,
K. H. KLOOS
(4
W
(4 Fig. 6. Fracture cross sections of ion-plated TIN coatings on substrates of different surface roughness (thermionically assisted triode ion plating; US = 1 kV; p,., = 5.6 x 10m3 mbar; i, = 1.5 mA cm-‘; r = 100 8, s-l): (a) polished substrate;(b) lapped substrate;(c) ground substrate.
ION-PLATED
TiN,TiC
AND
Ti(C,N)
COATINGS
251
Fig. 7. Fracture cross sections of ion-plated TiC coatings on substrates of different surface roughness (thermionically assisted triode ion plating; US = 1 kV; pAr = 5 x 10m3 mbar; i, = 0.9 mA cm-*; r = 300 A s-l): (a) polished substrate;(b) ground substrate.
coatings require significantly higher substrate current densities. All TiC coatings shown in Fig. 8 have a (111) preferred orientation. This orientation becomes stronger with increasing deposition rate. The hardness also increases up to 2720 HV 0.015 for the coatings with the strongest orientation (Fig. 8(c)). Both the strong (111) orientation and the high hardness are advantageous properties for tribological applications. The adhesion of all the coatings is perfect. Ion-plated Ti(C,N) coatings show an increasingly fibrous grain structure at increasing deposition rates (Fig. 9) with significantly unidirectional columns perpendicular to the substrate surface at high rates. The grain structure is influenced by the partial pressures, the substrate current density and the surface roughness similarly to TIN. All deposited coatings contain a certain amount of the s-Ti,N phase, which increases with increasing deposition rate. At low rates the TiN content is higher than that of TiC and vice versa at high rates. Hardnesses of up to 2150 HV 0.015 were obtained for Ti(C, N) coatings at a deposition rate of 300 A s-l. At higher rates the hardness decreased below 2000 HV 0.015.
252
H. M. GABRIEL,
K. H. KLOOS
(4
W
Fig. 8. Fracture cross sections of ion-plated TiC coatings at various deposition rates r (thermionically assisted triodeionplating; U, = 1 kV; pAr = 5 x lo-’ mbar; i, = 1.1 mAcm_‘; polished substrates): (a) r=
120.&s-‘;(b)r
= 3OOAs-‘;(c)r
= 5OOAs-‘.
ION-PLATED
TIN, TiC AND Ti(C,N) COATINGS
253
(4
(b)
Fig.‘9. Fracture cross sections of ion-plated Ti(C,N) coatings at various deposition rates r (thermionically assisted triode ion plating; U, = 1 kV; pAr = 5 x 1O-3 mbar; i, = 1 mA cm-*; polished substrates): (a)r = 150As-‘;(b)r= 3OOAs-‘;(c)r = TOOAs-‘.
254 4.
H. M. GABRIEL,
SUMMARIZING
K. H. KLOOS
REMARKS
This investigation clearly shows that the morphology, the grain structure, the stoichiometry and the texture of hard and wear-resistant carbide and nitride coatings produced by reactive ion plating are strongly influenced by the process parameters (substrate current density, partial pressures of the reactive gases and deposition rate) and by the substrate roughness. To form dense coatings it is necessary to enhance the ionization as was achieved with a thermionically assisted triode. With increasing current density the coatings become more compact and the adhesion is improved. The deposition rate influences the grain structure depending on the material to be deposited but also the orientation of the coating. The reactive gas partial pressures have to be correctly balanced with respect to the deposition rate to attain the correct stoichiometry as well as to obtain a dense grain structure. Stoichiometric coatings were produced over a very wide range of deposition rates. This investigation showed that hard wear-resistant coatings such as the carbides and nitrides of titanium can be produced by ion plating with a wide range of properties, i.e. morphology, structure and composition, according to their application4v9. ACKNOWLEDGMENT
The author wishes to thank the Deutsche Forschungsgemeinschaft (DFG) for their financial support. This paper is a contribution of the Sonderforschungsbereich 152 “Oberflachentechnik” of the DFG. This work is part of the Dr.-Ing. dissertation of H. M. Gabriel at the University of Darmstadt. REFERENCES 1 2 3 4 5 6 7 8 9 10
R. L. Hatschek, Coatings: revolution in HSS tools, Am. Mach., (March 1983) 129-144. K. Giihring and W. Kerschl, Hartstofibeschichtete Schneidwerkzeuge, Schneidwerkzeuge aus Schnellarbeitsstahl, Ind.-Anz., 102 (100) (1980) 12. K. H. Kloos, E. Broszeit, H. M. Gabriel and H. J. Schriider, Thin TiN coatings deposited onto nodular cast iron by ion- and plasma-assisted coating techniques, Thin Solid Films, 96 (1982) 67-77. H. M. Gabriel, F. Schmidt, E. Broszeit and K. H. Kloos, Improved component performance of vane pumps by ion-plated TIN coatings, Thin Solid Films, 108 (1983) 189. A. Matthews and D. G. Teer, Ion plated TIN coatings for dies and moulds, Proc. Int. Co& on Ion Plating and Allied Techniques, London, July 1979, CEP Consultants, Edinburgh, 1979, pp. 225-229. K. H. Kloos, E. Broszeit and H. M. Gabriel, Moglichkeiten der Ionisierungserhiihung beim Ion Plating Verfahren, Vuk.-Tech., 30 (1) (1981) 15-21. A. Matthews and D. G. Teer, Characteristics of a thermionically assisted triode ion plating system, Thin Solid Films, 80 (1981) 41-48. A. Matthews and D. G. Teer, Deposition of Ti-N compounds by thermionically assisted triode reactive ion plating, Thin Solid Films, 72 (1980) 541-549. K. H. Kloos, E. Broszeit, H. M. Gabriel and H. J. Schroder, Wear behaviour of hard coated cast iron, Wissenschaft und Technik, Vol. 20, University of Darmstadt, Darmstadt, 1983. H. M. Gabriel, Influence of ion bombardment on the substrate material, e.g. hardened ball-bearing steel En 31, Vuk.-Tech., to be published.