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TixAl1−xN films deposited by ion plating with an arc evaporator
Thin Solid Films, I53 (1987) 67-74
67
Ti,Al, -,N FILMS EVAPORATOR* H. FRELLER
DEPOSITED
BY ION PLATING
WITH
AN ARC
AND H. HAESSLER
Siemens AG.. Research and Development, Erlangen (F.R.G.) (Received
March 24, 1987)
Deposition experiments have been carried out to obtain T&Al, -,N coatings by the ion-bonding process and by magnetron sputter ion plating (MSIP). Aluminium concentrations of between 10 and 50 at.% in the source material were used for the deposition. The experimental results on the dependence of the hardness of the coatings on the nitrogen partial pressure, the structural features of the coating surface and fracture are discussed. The results also show that the ion-bonding process is well suited to the deposition of mixed compounds by the evaporation of alloys in reactive gas atmospheres. Compared with the aluminium concentration of the source material, the aluminium content in the deposited coating is reduced, while films deposited by the MSIP process show a small increase in aluminium concentration compared with that of the target. The observed dependence of the aluminium content on the bias voltage using the ion-bonding process offers an interesting possibility for changing the aluminium concentration in a growing film by variation in the bias voltage during the coating process.
1. INTRODUCTION
The theoretical analysis of hard compounds and their high temperature behaviour against iron by Kramer and Judd’, the review and experimental studies of Holleck2 and, last but not least, industrial practice indicate that a single hard compound such as TiN cannot be the unique choice for solution of the great variety of different wear problems. While there are many hard compounds having a high Vickers hardness of between 2000 and 2500, these hard compounds differ remarkably in their chemical, electrical and mechanical data such as thermal expansion coefficient and adhesion to steel3 or cemented carbide substrates. To utilize the considerable potential included in the combination of these properties, the application of mixed compound * Paper presented at the 14th International U.S.A., March 23-27, 1987, 0040-6090/87/.$3.50
Conference
on Metallurgical
Coatings,
0 Elsevier Sequoia/Printed
San Diego,
CA,
in The Netherlands
68
H. HAESSLER,
H. FRELLER
layers (i.e. ternary or quaternary compounds), sandwich layers of different materials and heterogeneous film mixtures is a necessity. The chemical vapour deposition (CVD) technique already utilizes this potential in the series of film combinations applied on carbide inserts for cutting operations4*5. The deposition of such improved films at temperatures below 500°C or, even better, below 300°C is the future challenge for physical vapour deposition (PVD) coating processes. Recently, Ti-Al-N films have become the subject of much attention because of their enhanced oxidation resistance6 and their improved cutting performance in drilling’ and turning operations in comparison with TiN*. Hot hardness measurements also indicate that Ti-Al-N has advantages compared with both CVD and PVD TiN coatings’ (Fig. 1). The deposition of these mixed compounds was hitherto mainly achieved by the use of ion-plating processes based on sputtering sources which created the particle flux to the substrate to be coated. Our work deals with the experimental results of deposition attempts to obtain Ti,Al, -,N coatings by the evaporation of Ti-Al alloys from an arc source in a nitrogen atmosphere,
Temperature
Fig. 1. TiN hot microhardness:
2.
EXPERIMENTAL
(“Cl
A, CVD TiN;
n , PVD
Ti-AI-N;
l , PVD
TiN.
DETAILS
A program was started to compare the usefulness of two different processes for depositing Ti-Al-N coatings. Source materials with various aluminium concentrations of the alloy were used in this program. The ion-plating processes used are magnetron sputter ion plating (MSIP) and the ion-bonding process which is based on arc sources (Fig. 2). Alloy targets or cathodes with lo,25 and 50 at.% Al were investigated. For the 10 at.% Al version the industrial alloy Ti-6wt.%Al-4wt.%V was used, because this material is readily available in sheet and rods. The other alloys were made by the powder metallurgy technique. The substrates used for the deposition experiments were D3 (1.2080) and D2 (1.2379) tool steels. The deposition experiments were performed under the conditions given in Table 1.
Ti, Al, -XN FILMS DEPOSITED
BY ION PLATING
WITH
ARC EVAPORATOR
69
TABLE I DEPOSITION
CONDITIONS
Parameter
MSIP
Working pressure (mbar) Reactive gas pressure (mbar) Coating temperature (“C) Bias voltage(V) Specific deposition rate (pm min- ’ kW_‘)
8~10-~ 1 x 10-‘-3x < 300 100 0.15
Ion bonding
10-3
1 x 10-3-5 x10-2 1 x1o-3-5x 1o-2 <300 100 (o-250) 0.1
3. RESULTS In our experiments with the single-target MSIP set-up shown schematically in Fig. 2, we found that the discrete Knoop hardness maxima depended on the nitrogen partial pressure for every target composition used (Fig. 3). The nitrogen partial pressure necessary to achieve this optimum hardness was found to increase with increasing aluminium concentration in the target which was used to deposit the coating. For experiments with a double-target magnetron, different results have been reported by Miinz, who had to use a higher nitrogen flow for targets with a lower aluminium content. ARC. IP
MSIP
@
Source
Material. p;;rial Plasma
Fig. 2. Ion-plating configurations with cathode sources.
Another marked difference between the MSIP and ion-bonding process can be observed. While the magnetron process produces hard coatings only in an extremely narrow region of nitrogen partial pressure, the arc process allows deposition over a broader, more easily controlled pressure region for the reactive gas (Fig. 3). The use of mass flow gas controllers is not necessary in this case. For the application of films on tools, adhesion is a very crucial parameter. In Fig. 4 the critical load F, and the critical deformation depth a,=, which is the depth of the scratch groove at the point of critical load, is plotted against the nitrogen mass flow or nitrogen partial pressure. Both the critical load and the critical depth show the same tendencies with respect to their dependences on the fraction of the reactive gas. In contrast with the critical load, however, which is strongly dependent on the
H. HAESSLER, H. FRELLER
70
3600 -
2 0
3200
-
r
2600
-
w @ ‘? 2400 e 8 g
2000
-
-
ISOOt 0 (a)
I 11 0.60
I
I
I I 1.20
I
1 I 1.60
Np pressure (mbar)
/
I t 2.40
I
I 5 ,0-z
I 5 @
I ,0-q
1 3.00 x10-3
III 3 5 ,o-l
N2 pressure (mbor)
(W
Fig. 3. Dependence of Knoop hardness on the nitrogen pressure: (a) MSIP (+, TiN obtained using 90% TiL6wt.%AlL4wt.%V; 0, TiN obtained using 75at.%Tik25at.%Al; *, TiN obtained using SOat.%TiSOat.%Al); (b) bias voltage of 100 V, a coating temperature of 250°C or less and an 84wt.%Ti-16wt.%Al source material (A, magnetron source, 82wt.%Ti-18wt.%Al; A, arc source, 9lwt.%Ti-9wt.%Al).
depth has nearly film thickness and substrate hardness lo, the critical deformation the same values for the thicker MSIP films (8-10 urn) and the thinner ion-bonded films (3-5 urn), both deposited from 75at.%Ti-25at.%Al alloy sources. This indicates that the critical deformation depth ~5,~ may possibly be a more unique value for determining adhesion than the critical load is. Further investigations will be carried out on this topic. It is interesting to note that the best adhesion is found for MSIP films at nitrogen flow values which correspond to hardness values slightly below the achieved maximum. For arc-deposited films, however, the best values for critical load and critical deformation depth are found for nitrogen pressures above the value for optimum hardness. Scanning electron microscopy (SEM) micrographs show a decrease in columnar film structure with increasing aluminium content, even at relatively low bias current densities for MSIP-deposited films. The film colour changes from golden via purple-gold to bluish-black when the aluminium content increases from 10 to 25 to 50 at.%. Investigations of the coatings using energy-dispersive X-ray analysis (EDXA) show good conformity of the aluminium concentrations of the target and the film deposited by MSIP process.
A--A
--_ -___
/’
‘A
6I Y-A
l--•
2’ 0’
IO-'
IO-'
IO-
Pp+ lmbor)
Fig. 4. Dependence of critical load F, (b) critical deformation depth 6rc (+) hardness (-A-) on the nitrogen fraction (bias voltage, 50 V); (a) MSIP; (b) ion-bonding
and Knoop process.
Ti,Al, _,N
FILMS DEPOSITED
BY ION PLATING
WITH
ARC EVAPORATOR
71
Experiments with the arc source using the Ti-6wt.%Al-4wt.%V alloy cathode led to golden coatings with hardness values and static deposition rates comparable with the MSIP process. SEM micrographs of the fracture cross-sections of these films reveal a similar columnar film structure while surface micrographs show a high density of small particles for arc-deposited films. MSIP layers with a comparable aluminium concentration show a low density of larger macroscopic particles on a relatively rough film surface. The results of EDXA measurements of the elemental concentration of the metallic components reveal the somewhat surprising fact that the films deposited by the arc process are remarkably depleted in aluminium in comparison with the cathode alloy. As a first step the cathode material was reinvestigated to ensure the proper bulk composition. There was good agreement with the manufacturer’s data. The surface of the Ti-6wt.%Al-4wt.%V cathode was a little depleted in aluminium and enriched in vanadium. These small changes, however, could not be responsible for a loss of nearly 50% of the aluminium content (Table II). TABLE II Ti-AI-N F~LMCOMPOS~T~ONFORVARIOUSSOURCECOMPOSII'IONSAND
Coating compositions
Source
Alloy
Ti-6wt.%Al-4wt.%V 75at.%Ti-25at.%AI 50at.%Ti-50at.%AI
PROCESSES
Composition
MSIP process
Ion-bonding process
(wt.%)
(wt.%)
(wt.%)
90Ti-6Al-4V 86Ti-14Al 68Ti-32Al
88Ti-6.6AI-4.W 82Ti-18Al 61Ti-39Al
91.3Ti-3.2AI-SSV 91Ti-9AI 70.5Ti-29.5Al
a For a bias voltage of 100V.
While sputtered particles are mainly neutral atoms (9573, a high degree of ionization is claimed for the particle stream emanating from an arc evaporation source. In the related literature ’ l-l3 , different percentages of ionization for different metals are reported. No data were available for the degree of ionization of vanadium in an arc source, but data available for aluminium and titanium show a higher degree of ionization in titanium vapours (80%) emanating from arc sources than in aluminium vapours (50%). These different degrees of ionization of the constituents of an alloy could be responsible for the demixing effect observed in our experiments. Ions are attracted by the negatively biased substrate in the ion-bonding process while neutral vapour particles show a cosine law distribution of vapour particles. Deposition runs with various bias voltages including zero bias should therefore show differences in the alloy film composition if such a phenomenon is responsible for the loss of aluminium. Figure 5 shows a comparison of the alloy compositions of the cathode materials and the compositions of films deposited at 0, 50, 100 and 250 V. Relatively good agreement can be seen between the cathode material and the films deposited without any bias voltage at the substrate. Increasing the bias voltage at the substrate decreases the aluminium concentration in the growing film significantly. The experiments with cathodes of higher aluminium concentration
72
H. HAESSLER,
H. FRELLER
show the same tendency for the aluminium content to decrease in thee coating compared with the composition of the source. The percen tage of the loss, however, decreases with increasing aluminium content in the source material.
Fig. 5. Influence of substrate bias voltage composition; n , A, 0, coating composition.
on the aluminium
Fig. 6. Surface micrographs of Ti-AI-N films deposited concentrations on variously biased substrates.
from
con, centration:
0,
A,
cath lodes with
various
0,
source
aluminium
Ti,Al,
_ XN FILMS DEPOSITED BY ION PLATING WITH
ARC
EVAPORATOR
13
Micrographs of the surface and of the fracture cross-sections of the deposited films are shown in Fig. 6 and Fig. 7 respectively. No significant influence of bias voltage or of the aluminium content of the films is detectable in the morphology of the fracture cross-sections of the films. In contrast with this a strong influence of the bias voltage on surface topography is observed, while the influence of the aluminium content of the films seems to be of minor importance. 0
50
Al at?&
25
Fig. 7 Micrographs of fracture cross-sections of Ti-AI-N films deposited from cathodes with various aluminium concentrations on variously biased substrates
4. SUMMARY The attempts to deposit hard wear-resistant Ti,Al,_,N mixed compound coatings by two variants of the ion-plating process were successful. Comparison of the results has confirmed the speculative assumption that ion-plating processes using an arc source should also be able to deposit mixed compounds by reactive deposition using an alloy source. In contrast with the deposition results using a magnetron sputtering source, the
74
H. HAESSLER,
H. FRELLER
coatings deposited with the arc source show a depletion of aluminium in the coating compared with the source. The observed influence of the bias voltage on the aluminium concentration in the coating offers an interesting possibility for changing the composition of the coating during growth within the detected limits. ACKNOWLEDGMENTS
The authors are greatly indebted to Miss Gabi Bichler, Mr. Joachim Lilge and Peter Schack for assistance in the coating experiments and measurement of the mechanical properties of the coatings. We acknowledge the help of Mrs. Gudrun Kuesebauch in obtaining the SEM micrographs and the EDXA results. This work was partially supported (MSIP process) by financial aid from the Ministry for Research and Technology of F.R.G. under Contract 13 N 5373/6. REFERENCES
2 4 5 6 7 8 9 10 11 12 13
P. M. Kramer and P. K. Judd, J. Vat. Sci. Technol. A, 3 (1985) 2439. H. Holleck, J. Vuc. Sci. Technol. A, 4 (1986) 2661. J. E. Sundgren and H. T. Hentzell, J. Vuc. Sci. Technol. A, 4 (1986) 2259. U. Kiinig, K. Dreyer, N. Reiter, J. Kolaska and H. Grewe, Tech. Mitt. Krupp, Forschungsber., 39 (1981) 13. W. Schintlmeister, W. Wallgram and K. Gigl, in H. Ortner (ed.), Proc. llth Int. Plansee Sem., 1985, Vol. 2, Metallwerk Plansee, Reutte, 1985, p. 299. W. D. Miinz, J. Vat. Sci. Technol. A, 4(1986) 2717. 0. Knotek, T. Leyendecker and W. D. Miinz, Proc. 10th Intern. Vat. Congr. October 27-31. Baltimore, MO, J. Vat. Sci. Technol. A, 5 (1987) to be published. 0. Knotek, W. Bosch and T. Leyendecker, Proc. 11th Znt. Plansee Sem., 1985, Vol. 1, Metallwerk Plansee, Reutte, 1985, p. 611. G. J. Wolfe, personal communication, courtesy Kennametal Inc. (1986). P. A. Steinmann and H. E. Hintermann, J. Vuc. Sci. Technol. A, 3 (1985) 2394. W. D. Davis and H. C. Miller, J. Appl. Phys., 40 (1968) 2212. C. W. Kimblin, J. Appl. Phys., 44 (1973) 3074. C. Bergmann, personal communication, courtesy Multi-Arc Vacuum Systems (1986).
67
Ti,Al, -,N FILMS EVAPORATOR* H. FRELLER
DEPOSITED
BY ION PLATING
WITH
AN ARC
AND H. HAESSLER
Siemens AG.. Research and Development, Erlangen (F.R.G.) (Received
March 24, 1987)
Deposition experiments have been carried out to obtain T&Al, -,N coatings by the ion-bonding process and by magnetron sputter ion plating (MSIP). Aluminium concentrations of between 10 and 50 at.% in the source material were used for the deposition. The experimental results on the dependence of the hardness of the coatings on the nitrogen partial pressure, the structural features of the coating surface and fracture are discussed. The results also show that the ion-bonding process is well suited to the deposition of mixed compounds by the evaporation of alloys in reactive gas atmospheres. Compared with the aluminium concentration of the source material, the aluminium content in the deposited coating is reduced, while films deposited by the MSIP process show a small increase in aluminium concentration compared with that of the target. The observed dependence of the aluminium content on the bias voltage using the ion-bonding process offers an interesting possibility for changing the aluminium concentration in a growing film by variation in the bias voltage during the coating process.
1. INTRODUCTION
The theoretical analysis of hard compounds and their high temperature behaviour against iron by Kramer and Judd’, the review and experimental studies of Holleck2 and, last but not least, industrial practice indicate that a single hard compound such as TiN cannot be the unique choice for solution of the great variety of different wear problems. While there are many hard compounds having a high Vickers hardness of between 2000 and 2500, these hard compounds differ remarkably in their chemical, electrical and mechanical data such as thermal expansion coefficient and adhesion to steel3 or cemented carbide substrates. To utilize the considerable potential included in the combination of these properties, the application of mixed compound * Paper presented at the 14th International U.S.A., March 23-27, 1987, 0040-6090/87/.$3.50
Conference
on Metallurgical
Coatings,
0 Elsevier Sequoia/Printed
San Diego,
CA,
in The Netherlands
68
H. HAESSLER,
H. FRELLER
layers (i.e. ternary or quaternary compounds), sandwich layers of different materials and heterogeneous film mixtures is a necessity. The chemical vapour deposition (CVD) technique already utilizes this potential in the series of film combinations applied on carbide inserts for cutting operations4*5. The deposition of such improved films at temperatures below 500°C or, even better, below 300°C is the future challenge for physical vapour deposition (PVD) coating processes. Recently, Ti-Al-N films have become the subject of much attention because of their enhanced oxidation resistance6 and their improved cutting performance in drilling’ and turning operations in comparison with TiN*. Hot hardness measurements also indicate that Ti-Al-N has advantages compared with both CVD and PVD TiN coatings’ (Fig. 1). The deposition of these mixed compounds was hitherto mainly achieved by the use of ion-plating processes based on sputtering sources which created the particle flux to the substrate to be coated. Our work deals with the experimental results of deposition attempts to obtain Ti,Al, -,N coatings by the evaporation of Ti-Al alloys from an arc source in a nitrogen atmosphere,
Temperature
Fig. 1. TiN hot microhardness:
2.
EXPERIMENTAL
(“Cl
A, CVD TiN;
n , PVD
Ti-AI-N;
l , PVD
TiN.
DETAILS
A program was started to compare the usefulness of two different processes for depositing Ti-Al-N coatings. Source materials with various aluminium concentrations of the alloy were used in this program. The ion-plating processes used are magnetron sputter ion plating (MSIP) and the ion-bonding process which is based on arc sources (Fig. 2). Alloy targets or cathodes with lo,25 and 50 at.% Al were investigated. For the 10 at.% Al version the industrial alloy Ti-6wt.%Al-4wt.%V was used, because this material is readily available in sheet and rods. The other alloys were made by the powder metallurgy technique. The substrates used for the deposition experiments were D3 (1.2080) and D2 (1.2379) tool steels. The deposition experiments were performed under the conditions given in Table 1.
Ti, Al, -XN FILMS DEPOSITED
BY ION PLATING
WITH
ARC EVAPORATOR
69
TABLE I DEPOSITION
CONDITIONS
Parameter
MSIP
Working pressure (mbar) Reactive gas pressure (mbar) Coating temperature (“C) Bias voltage(V) Specific deposition rate (pm min- ’ kW_‘)
8~10-~ 1 x 10-‘-3x < 300 100 0.15
Ion bonding
10-3
1 x 10-3-5 x10-2 1 x1o-3-5x 1o-2 <300 100 (o-250) 0.1
3. RESULTS In our experiments with the single-target MSIP set-up shown schematically in Fig. 2, we found that the discrete Knoop hardness maxima depended on the nitrogen partial pressure for every target composition used (Fig. 3). The nitrogen partial pressure necessary to achieve this optimum hardness was found to increase with increasing aluminium concentration in the target which was used to deposit the coating. For experiments with a double-target magnetron, different results have been reported by Miinz, who had to use a higher nitrogen flow for targets with a lower aluminium content. ARC. IP
MSIP
@
Source
Material. p;;rial Plasma
Fig. 2. Ion-plating configurations with cathode sources.
Another marked difference between the MSIP and ion-bonding process can be observed. While the magnetron process produces hard coatings only in an extremely narrow region of nitrogen partial pressure, the arc process allows deposition over a broader, more easily controlled pressure region for the reactive gas (Fig. 3). The use of mass flow gas controllers is not necessary in this case. For the application of films on tools, adhesion is a very crucial parameter. In Fig. 4 the critical load F, and the critical deformation depth a,=, which is the depth of the scratch groove at the point of critical load, is plotted against the nitrogen mass flow or nitrogen partial pressure. Both the critical load and the critical depth show the same tendencies with respect to their dependences on the fraction of the reactive gas. In contrast with the critical load, however, which is strongly dependent on the
H. HAESSLER, H. FRELLER
70
3600 -
2 0
3200
-
r
2600
-
w @ ‘? 2400 e 8 g
2000
-
-
ISOOt 0 (a)
I 11 0.60
I
I
I I 1.20
I
1 I 1.60
Np pressure (mbar)
/
I t 2.40
I
I 5 ,0-z
I 5 @
I ,0-q
1 3.00 x10-3
III 3 5 ,o-l
N2 pressure (mbor)
(W
Fig. 3. Dependence of Knoop hardness on the nitrogen pressure: (a) MSIP (+, TiN obtained using 90% TiL6wt.%AlL4wt.%V; 0, TiN obtained using 75at.%Tik25at.%Al; *, TiN obtained using SOat.%TiSOat.%Al); (b) bias voltage of 100 V, a coating temperature of 250°C or less and an 84wt.%Ti-16wt.%Al source material (A, magnetron source, 82wt.%Ti-18wt.%Al; A, arc source, 9lwt.%Ti-9wt.%Al).
depth has nearly film thickness and substrate hardness lo, the critical deformation the same values for the thicker MSIP films (8-10 urn) and the thinner ion-bonded films (3-5 urn), both deposited from 75at.%Ti-25at.%Al alloy sources. This indicates that the critical deformation depth ~5,~ may possibly be a more unique value for determining adhesion than the critical load is. Further investigations will be carried out on this topic. It is interesting to note that the best adhesion is found for MSIP films at nitrogen flow values which correspond to hardness values slightly below the achieved maximum. For arc-deposited films, however, the best values for critical load and critical deformation depth are found for nitrogen pressures above the value for optimum hardness. Scanning electron microscopy (SEM) micrographs show a decrease in columnar film structure with increasing aluminium content, even at relatively low bias current densities for MSIP-deposited films. The film colour changes from golden via purple-gold to bluish-black when the aluminium content increases from 10 to 25 to 50 at.%. Investigations of the coatings using energy-dispersive X-ray analysis (EDXA) show good conformity of the aluminium concentrations of the target and the film deposited by MSIP process.
A--A
--_ -___
/’
‘A
6I Y-A
l--•
2’ 0’
IO-'
IO-'
IO-
Pp+ lmbor)
Fig. 4. Dependence of critical load F, (b) critical deformation depth 6rc (+) hardness (-A-) on the nitrogen fraction (bias voltage, 50 V); (a) MSIP; (b) ion-bonding
and Knoop process.
Ti,Al, _,N
FILMS DEPOSITED
BY ION PLATING
WITH
ARC EVAPORATOR
71
Experiments with the arc source using the Ti-6wt.%Al-4wt.%V alloy cathode led to golden coatings with hardness values and static deposition rates comparable with the MSIP process. SEM micrographs of the fracture cross-sections of these films reveal a similar columnar film structure while surface micrographs show a high density of small particles for arc-deposited films. MSIP layers with a comparable aluminium concentration show a low density of larger macroscopic particles on a relatively rough film surface. The results of EDXA measurements of the elemental concentration of the metallic components reveal the somewhat surprising fact that the films deposited by the arc process are remarkably depleted in aluminium in comparison with the cathode alloy. As a first step the cathode material was reinvestigated to ensure the proper bulk composition. There was good agreement with the manufacturer’s data. The surface of the Ti-6wt.%Al-4wt.%V cathode was a little depleted in aluminium and enriched in vanadium. These small changes, however, could not be responsible for a loss of nearly 50% of the aluminium content (Table II). TABLE II Ti-AI-N F~LMCOMPOS~T~ONFORVARIOUSSOURCECOMPOSII'IONSAND
Coating compositions
Source
Alloy
Ti-6wt.%Al-4wt.%V 75at.%Ti-25at.%AI 50at.%Ti-50at.%AI
PROCESSES
Composition
MSIP process
Ion-bonding process
(wt.%)
(wt.%)
(wt.%)
90Ti-6Al-4V 86Ti-14Al 68Ti-32Al
88Ti-6.6AI-4.W 82Ti-18Al 61Ti-39Al
91.3Ti-3.2AI-SSV 91Ti-9AI 70.5Ti-29.5Al
a For a bias voltage of 100V.
While sputtered particles are mainly neutral atoms (9573, a high degree of ionization is claimed for the particle stream emanating from an arc evaporation source. In the related literature ’ l-l3 , different percentages of ionization for different metals are reported. No data were available for the degree of ionization of vanadium in an arc source, but data available for aluminium and titanium show a higher degree of ionization in titanium vapours (80%) emanating from arc sources than in aluminium vapours (50%). These different degrees of ionization of the constituents of an alloy could be responsible for the demixing effect observed in our experiments. Ions are attracted by the negatively biased substrate in the ion-bonding process while neutral vapour particles show a cosine law distribution of vapour particles. Deposition runs with various bias voltages including zero bias should therefore show differences in the alloy film composition if such a phenomenon is responsible for the loss of aluminium. Figure 5 shows a comparison of the alloy compositions of the cathode materials and the compositions of films deposited at 0, 50, 100 and 250 V. Relatively good agreement can be seen between the cathode material and the films deposited without any bias voltage at the substrate. Increasing the bias voltage at the substrate decreases the aluminium concentration in the growing film significantly. The experiments with cathodes of higher aluminium concentration
72
H. HAESSLER,
H. FRELLER
show the same tendency for the aluminium content to decrease in thee coating compared with the composition of the source. The percen tage of the loss, however, decreases with increasing aluminium content in the source material.
Fig. 5. Influence of substrate bias voltage composition; n , A, 0, coating composition.
on the aluminium
Fig. 6. Surface micrographs of Ti-AI-N films deposited concentrations on variously biased substrates.
from
con, centration:
0,
A,
cath lodes with
various
0,
source
aluminium
Ti,Al,
_ XN FILMS DEPOSITED BY ION PLATING WITH
ARC
EVAPORATOR
13
Micrographs of the surface and of the fracture cross-sections of the deposited films are shown in Fig. 6 and Fig. 7 respectively. No significant influence of bias voltage or of the aluminium content of the films is detectable in the morphology of the fracture cross-sections of the films. In contrast with this a strong influence of the bias voltage on surface topography is observed, while the influence of the aluminium content of the films seems to be of minor importance. 0
50
Al at?&
25
Fig. 7 Micrographs of fracture cross-sections of Ti-AI-N films deposited from cathodes with various aluminium concentrations on variously biased substrates
4. SUMMARY The attempts to deposit hard wear-resistant Ti,Al,_,N mixed compound coatings by two variants of the ion-plating process were successful. Comparison of the results has confirmed the speculative assumption that ion-plating processes using an arc source should also be able to deposit mixed compounds by reactive deposition using an alloy source. In contrast with the deposition results using a magnetron sputtering source, the
74
H. HAESSLER,
H. FRELLER
coatings deposited with the arc source show a depletion of aluminium in the coating compared with the source. The observed influence of the bias voltage on the aluminium concentration in the coating offers an interesting possibility for changing the composition of the coating during growth within the detected limits. ACKNOWLEDGMENTS
The authors are greatly indebted to Miss Gabi Bichler, Mr. Joachim Lilge and Peter Schack for assistance in the coating experiments and measurement of the mechanical properties of the coatings. We acknowledge the help of Mrs. Gudrun Kuesebauch in obtaining the SEM micrographs and the EDXA results. This work was partially supported (MSIP process) by financial aid from the Ministry for Research and Technology of F.R.G. under Contract 13 N 5373/6. REFERENCES
2 4 5 6 7 8 9 10 11 12 13
P. M. Kramer and P. K. Judd, J. Vat. Sci. Technol. A, 3 (1985) 2439. H. Holleck, J. Vuc. Sci. Technol. A, 4 (1986) 2661. J. E. Sundgren and H. T. Hentzell, J. Vuc. Sci. Technol. A, 4 (1986) 2259. U. Kiinig, K. Dreyer, N. Reiter, J. Kolaska and H. Grewe, Tech. Mitt. Krupp, Forschungsber., 39 (1981) 13. W. Schintlmeister, W. Wallgram and K. Gigl, in H. Ortner (ed.), Proc. llth Int. Plansee Sem., 1985, Vol. 2, Metallwerk Plansee, Reutte, 1985, p. 299. W. D. Miinz, J. Vat. Sci. Technol. A, 4(1986) 2717. 0. Knotek, T. Leyendecker and W. D. Miinz, Proc. 10th Intern. Vat. Congr. October 27-31. Baltimore, MO, J. Vat. Sci. Technol. A, 5 (1987) to be published. 0. Knotek, W. Bosch and T. Leyendecker, Proc. 11th Znt. Plansee Sem., 1985, Vol. 1, Metallwerk Plansee, Reutte, 1985, p. 611. G. J. Wolfe, personal communication, courtesy Kennametal Inc. (1986). P. A. Steinmann and H. E. Hintermann, J. Vuc. Sci. Technol. A, 3 (1985) 2394. W. D. Davis and H. C. Miller, J. Appl. Phys., 40 (1968) 2212. C. W. Kimblin, J. Appl. Phys., 44 (1973) 3074. C. Bergmann, personal communication, courtesy Multi-Arc Vacuum Systems (1986).