- Email: [email protected]
PVD coating of 3D parts studied with model samples
ELSEVIER
Surface and Coatings Technology
94-95
(1997) 232-236
PVD coating of 3D parts studied with model samples Hermann
A. Jehnaq*, Bernd Rothera, Herbert Kappl”, Gerhard Ebersbachb
“Forschrcngsinstitut fiir Edeimeralle und Metallchemie, Kuthnrinenstr. 17, D-3525 Schwtibisch Gmiind, Germany bInsrirur fiir Physikalische und Mechwkche Technologie, iksaliestr. 10, D-091 17 Chemnilz, Germany
Abstract TiN coatings are deposited by reactive magnetron sputtering, cathodic arc evaporation and hollow cathode discharge arc evaporation on high speed steel samples representing different 3D profiles. The thickness, morphology and hardness distribution on the model samples are determined for a double magnetron, an unbalanced magnetron, a hollow cathode discharge and a cathodic arc evaporation laboratory arrangement, and an industrial two-source cathodic arc deposition system. The properties depend strongly on the deposition technique, the angle of incidence, the deposition conditions (with and without sample movement) and the profile depth of the groove and wedge samples. 0 1997 Elscvier Science S.A. Keywords:
Three-dimensional
profiles; PVD coatings; Model samples
1. Introduction
2. Experimental
PVD coating of hard and protective coatings gains more and more importance. Coating properties and their dependence on process parameters have been intensively studied, in most cases, however, for small and flat samples only. In most of the industrial applications three-dimensional parts have to be coated which show a more or less complex shape, e.g. tools, bearings, machine parts and even decorative articles. The PVD processes are characterised by directed fluxes of neutral and ionised particles from the source to the substrate. This line-of-sight process means, in consequence, that different growth conditions exist for different surface areas with respect to source-to-substrate distance and orientation, i.e. flux density and angle of incidence. The parts are normally moved in order to yield a more homogeneous coating deposition. The effect of sample shape, orientation and distance have only scarcely been studied up to now [l-6]. More recently, the film thickness and property distribution in a number of model samples has been studied for magnetron-sputtered hard coatings [7]. The present paper reports on extended investigations using also the hollow cathode discharge arc evaporation and the cathodic arc evaporation in static and dynamic sample positions in laboratory and industrial equipment.
2.1. Samples
*Corresponding author. Tel.: +49 7171 100654; e-mail: femmail@compuse~e.com
10062126;
fax: +49 7171
02.57~8972/97/$17.00 0 1997 Elsevier Science S.A. All righlb reserved PII SO257-8972(97)00424-6
Mirror polished 2-mm thick high speed steel (HSS) platelets were used as substrate material. The different threedimensional (3D) profiles were realised by suitable mounting of these platelets. This technique allowed an easy characterisation of the coatings as a function of the position of the substrate areas after demounting. The following shapes were selected as 3D mode samples: U-groove of different depths, V-groove and V-wedge of different angles and, hence, of different depths (see Fig. 1). The upper width of the U-grooves and the V-grooves was 10 mm. The extension of the samples perpendicular to the drawing plane was 50 mm. 2.2. Coating deposition Because of the importance of a homogeneous coating process for many tribological - and also decorative applications, TiN was selected as coating material. It was deposited by various reactive PVD techniques, i.e. double magnetron (DM), unbalanced magnetron (UBM), cathodic arc deposition (CAD) and hollow cathode discharge arc evaporation (HCD). These deposition techniques are characterised as follows: The double magnetron is formed by a pair of opposed balanced magnetrons; both were powered
HA.
Jehn et a!. /Surface
and Coniings
but the model samples were faced to only one of them. The unbalanced magnetron has a plasma extended by an additional magnetic field towards the substrate. Cathodic arc deposition (solid source) and hollow cathode discharge arc evaporation (liquid source) are characterised especially by their high degree of ionisation of the vaporised atoms and the high energy of the particles even increased by a bias voltage. The samples were coated in static and dynamic (rotating) positions. Fig. 2 illustrates the geometrical ar-rangements in the laboratory and industrial coating devices. After thorough wet cieaning of the platelets in ultrasonic baths, the samples were composed and mounted in the deposition system and sputter-cleaned prior to the coating procedure. A thin Ti interlayer was first deposited to ensure good adhesion of the TiN coatings. The parameters of the coating deposition are summarised in Table 1. 2.3. Coating
Technology
94-95
(1997)
232-236
Schematic deposition principles static:
00
xl
dynamic: DM, CAD, HCD
DM, UBM, CAD, HCD
Industrial deposition principle
chnructerisation
The coatings were characterised for thickness, morphology and hardness as a function of the profile depth which is characterised as perpendicular distance from the outermost part of the profile (see Fig. 1). The thickness and morphology were determined by the calotest and scanning electron microscopy of fracture surfaces, respectively. The thin film thicknesses were normalised to the thickness of a plane sample positioned at the outermost part of the profile directed to the source. The hardness was characterised by depthsensing indentation measurements (Vickers pyramid) which were evaluated in terms of hardness equivalents [ 8 -101. The latter is an indenter-specific density of the deformation energy which is better suited for the characterisation of coating-substrate systems than the conventional hardness values. This method is particularly applicable to the characterisation of very thin films. In part the hardness was also characterised by the universal hardness (indentation depth under load) using a Knoop indentor (HUK). Other tests covered thickness by X-ray fluorescence analysis, surface roughness by laser stylus profilometry, chemical composition by glow discharge optical spectroscopy, colour as well as wear and friction, but in a less complete
Particle fluxes
..~
. . . . .
. ;;$
,
,2cm,
Plane
U-groove
i
/’ Wedge V-groove 11 Angle
Fig. 1. Model samples for 3D part coating studies.
II Flux source(s) Fig. 2. Schematic arrangement deposition.
x
Substrate(s)
of samples in static and dynamic coating
manner. The results shall not be discussed here in detail and are reported elsewhere [ 111.
3. Results and discussion 3.1. Coating
thickness
In Fig. 3a-c, the major results of the thickness measurements are summarised. The following general statements can be made. (i) A marked decrease of the coating thickness is noted for higher profile depths. This holds for the bottom of the Ugroove as well as the side wall of the U-groove and the Vgroove. For wedges a lower thickness is noted in the nearedge area due to material loss by sputtering processes. In the V-grooves, in contrast, the same sputtering processes cause no effective material loss. The dependencies plotted in Fig. 3a for coatings deposited in the double magnetron arrangement with static sample position reflect qualitatively the distribution in the other coating processes with static sample positions. The angle of incidence expectedly influences the absolute coating thickness also at the uppermost area. The coating thickness decreases with decreasing angle. -(ii) The characteristics of the different PVD processes also influence the thickness distribution on 3D samples. This is mainly caused by the different flux and energy distributions of the film-forming and modifying particles. Typical examples for these effects are shown in Fig. 3b using the bottom of the U-grooves and the 54”-V-groove with static deposition principle. A major characteristic of the plots is the stronger decrease in thickness with profile depth for magnetron sputtering (DM, UBM) values com-
234
HA. Jehn et al. / Sutfuce and Coatings Technology
94-S
(1997) 232-236
Table 1 Experimental
conditions UBM
HCD
CAD
CAD (ind.)
300 Ar’, 40 0.1
300 A?, 40 0.1
300 Ar’ 0.1
300 Ar-, Ti0.1
300 At-‘, Ti+ 0.1
5 x 10-3 9 x lo-? Ark& 300 -100 8
5 x 10-3
5 x 1o-3
5 x 1O-3
atmosphere Substrate temp. (“C) Substrate bias (V) Source-substrate distance (cm)
5 x 1o-3 2 x 10-Z Ar& 300 -100 5 20
W 200 -50 14 21 20
N, 400 -50 min 25
Deposition
AT/N? 460 -50 14 21 20
DM Static Preueatment Heating (“C) Ion etching (min) Ti interlayer (pm) Tii deposition Pressure (mbarj
time
Dynamic
240
55
120
DM, double magnetron, Leybold Z 700; WM, unbalanced magnetron, laboratory system; HCD, hollow cathode discharge, semi-industrial IPMT; CAD (irk), cathodic arc deposition, PVT 840.
pared with the arc techniques (HCD, CAD). This can be attributed to the higher degree of ionisation of the metal vapour in HCD and CAD which results in a better depth efficiency. This trend found with U-groove and 54’-Vgroove samples also holds for the other V-groove and wedge samples. An exception is the 30”-V-groove which shows an almost constant film thickness along the profile depth (Fig. 3b, lower left diagram). It is assumed that this relatively high and constant thickness is caused by the enhanced sputtering efficiency for low-angle ion incidence. This effect is more pronounced for UBM than for balanced sputtering (DM). In HCD and CAD this effect is not observed because the denser plasmas in those arrangements follow more strictly the shape of the surface and result in an incidence more perpendicular to the surface. (iii) The effect of sample movement (dynamic deposition) is illustrated in Fig. 3c, showing the results for the slightly curved motion in front of the inner cathode of the double magnetron arrangement and for the twofold rotation of the industrial two-target cathodic arc deposition device. The results show a stronger decrease of the thickness with increasing profile depths due to partial shadowing of the deeper groove areas when the samples are not directly oriented to the target. This effect becomes more pronounced with deeper grooves (higher aspect ratio). In orienting measurements the influence of the source-to-substrate distance, the working gas pressure and the bias voltage were studied. The trends (iv) and (v) have been observed. (iv) For larger source-to-substrate distances a relatively lower deposition rate exists. The decrease of the coating thickness with increasing profile depth for U- and Vgrooves is similar to samples mounted in a smaller distances. (v) An increased working gas pressure results in a markedly higher film thickness in the outer parts of the grooves.
systems, GFE-
This results from increased scattering effects in the transport space. Simultaneously, the deeper areas show a reduced thickness when compared with the deposition at lower pressures. 3.2. Morphology The morphology of PVD coatings in relation to the phenomena considered in this study depends strongly on the angle of incidence, the energy of the impinging atoms/ ions and the deposition rate. Fig. 4 shows the morphology of the TiN coatings deposited on different wedges together with the film on a plane substrate. For perpendicular incidence in static deposition a perpendicular orientation of the columnar crystallites is built up, and other angles of incidence result in a crystal growth directed towards the source. But a maximum deviation from the perpendicular growth is found even for a 30”~wedge. The comparison of the structure formed on the 30”-wedge in the double magnetron with the unbalanced magnetron deposition shows a much more perpendicular growth in the latter case due to the more intense ion bombardment of the growing film. The continuously varying incidence on rotating substrates (dynamic deposition) also yields a much less columnar and almost perpendicularly oriented structure. This holds especially for the twofold rotation in the industrial coating device. Another fact has to be noted, namely, the morphology in the very near-edge region of the wedge samples is almost featureless. This is attributed to the increased ion flux due to the enhanced electrical field in the vicinity of the edges. Details of this effect are described elsewhere [ 121. 3.3. Hardness The hardness of the coatings deposited on the side-
H.A. John et al. / Suq?zce rind Coatings Techno!ogy 94-95
Double magnetron,
static deposition
235
(1997) 232-236
DM, stat.
UBM, stat.
DM, dyn.
90” wedge
90” wedge
plane
30” wedge
30” wedge
30” wedge
Profile depth [mm]
b
Processes, U-groove:
static deposition side walls, depth 20 mm
bottom
mj
--2-pm Fig. 4. Coating morphology
0
5
10
15
10
20
15
coating conditions.
wall (U-groove) and the differently shaped V-grooves and wedges, in general, is lower than that of the reference plane; in part even lower than the substrate material. Exceptions are the dynamically deposited CAD coatings. This reflects the difficulties to deposit hard coatings on com-plexshaped substrates and especially in grooves by static magnetron sputtering. These relations shall therefore not be discussed in more detail. However, in the near-edge regions of the dynamic CAD coatings, constant and even increasing HE values are measured. This effect can in part be related to the already mentioned increased ion flux. A surprising effect, however, was found at the bottom of the U-grooves with sputtered films. Nearly constant HE values were found for all profile depths (Fig. 5), an effect which is not yet understood.
20
Profile de;th [im] C
for different
Processes, dynamic deposition CAD DM U-aroove. bottom
-
3.4. Other properties
I
,
0
5
10
15 20 25
0
5
10
1.5 20 25
Profile depth [mm] Fig. 3. Coating thickness distri&tion on model samples. (a) Effect of sample shape; (b) effect of PVD process; (c) effect of sample movement.
As already mentioned, the colour of the films was also determined. The golden colour of the sputtered TiN coatings changes into greyish or blackish for deeper groove and wall areas of magnetron-coated samples, indicating a change of composition and morphology. This was not found for CAD because that deposition process is less sensitive to variations in the process parameters such as nitrogen gas pressure and source-to-substrate distance.
236
HA. Jehn et al. /Su$ace
nnn,
U-aroove
and Conrings Terhnology
-0-
(1997) 232-236
Acknowledgements
(bottom)
LUU
t
94-95
These investigations were in part funded by the German Federal Ministry of Economic Affairs under contract number AiF 9138. This support is gratefully acknowledged.
5~10~ mbar, stat.
mpo2 ;;;lOOI
_^ SUI
l’
-@-~55x10~
,
0
References
mbar, dyn.
1 20
Fig. 5. Hardness of TiN coatings on 3D model parts.
4. Conclusion Differently shaped model samples were coated by different reactive PVD processes in laboratory and industrial equipment (double magnetron sputtering, unbalanced magnetron sputtering, hollow cathodic discharge evaporation and cathodic arc deposition) with and without sample motion. U-groove, V-groove and wedges with different angles and depths were selected as model samples. Coating thickness, morphology and hardness were measured as a function of the geometry and profile depth and compared to the coating deposited on a flat sample. The properties of the coatings can be explained by the influence of the different process parameters (PVD method, substrate-to-source orientation and distance, shadowing and electrical field effects). The use of demountable model samples and the applied measurement technique allow statements to be made on the realistic coating behaviour deduced from model experiments.
111B.O.
Johansson, J.-E. Sundgren, H.T.G. Hentzel and S.E. Karlsson, Thin Solid Films, Ill (1984) 313. 121M. Zlatanovic, R. Belosevac, A. Kunosk, N Popovk and 2. Bogdanov, Sllljf Coar. Technol., 74/75 (1995) 844. and H.A. Jehn, Suti Coat. [31 B. Rother, H. Kappl. I. Pfeikr-Schlller Technol., 79 (1996) 225. [41 C. Klatt, B. Enders and G.K. Wolf, Sulf: Coat. Technol., 74/Z (1995) 966. PI AS. James, S.J. Young and A. Matthews, SUI$ Coat. Technol., 74/Z5 (1995) 306. [61 KS. Fancey, Sw$ Coat. Technoi., 71 (1995) 16. 171 B. Rother, H. Kappl, I. Pfeifer-SchUler, G. Ebersbach and H.A. Jehn, to be published in SuQI Coat. Technol (Proc. Conf. Plasma Surface Engineering, Garmisch-Partenkirchen. 1996, Paper TrOA 2). PI B. Rothcr and D.A. Dietrich, Su5f: Coat. Technol., 74/75 (1995) 614. 191 B. Rother and H. Jehn, Szu$ Coat. Technol., 8.5 (1996) 183. Bad [lOI B. Rother and H. Jehn, Proc. DVM ConJ Werksto&@mg, Nauheim, 1995, p. 389. [Ill B. Rother, Final Report Research Project AiF 9138B, 1995. [I21 B. Rother, H. Kappl, I. Pfeifer-SchLllcr and H.A. Jehn, Su$ Coat. Technol., 79 (1996’i 225.
Surface and Coatings Technology
94-95
(1997) 232-236
PVD coating of 3D parts studied with model samples Hermann
A. Jehnaq*, Bernd Rothera, Herbert Kappl”, Gerhard Ebersbachb
“Forschrcngsinstitut fiir Edeimeralle und Metallchemie, Kuthnrinenstr. 17, D-3525 Schwtibisch Gmiind, Germany bInsrirur fiir Physikalische und Mechwkche Technologie, iksaliestr. 10, D-091 17 Chemnilz, Germany
Abstract TiN coatings are deposited by reactive magnetron sputtering, cathodic arc evaporation and hollow cathode discharge arc evaporation on high speed steel samples representing different 3D profiles. The thickness, morphology and hardness distribution on the model samples are determined for a double magnetron, an unbalanced magnetron, a hollow cathode discharge and a cathodic arc evaporation laboratory arrangement, and an industrial two-source cathodic arc deposition system. The properties depend strongly on the deposition technique, the angle of incidence, the deposition conditions (with and without sample movement) and the profile depth of the groove and wedge samples. 0 1997 Elscvier Science S.A. Keywords:
Three-dimensional
profiles; PVD coatings; Model samples
1. Introduction
2. Experimental
PVD coating of hard and protective coatings gains more and more importance. Coating properties and their dependence on process parameters have been intensively studied, in most cases, however, for small and flat samples only. In most of the industrial applications three-dimensional parts have to be coated which show a more or less complex shape, e.g. tools, bearings, machine parts and even decorative articles. The PVD processes are characterised by directed fluxes of neutral and ionised particles from the source to the substrate. This line-of-sight process means, in consequence, that different growth conditions exist for different surface areas with respect to source-to-substrate distance and orientation, i.e. flux density and angle of incidence. The parts are normally moved in order to yield a more homogeneous coating deposition. The effect of sample shape, orientation and distance have only scarcely been studied up to now [l-6]. More recently, the film thickness and property distribution in a number of model samples has been studied for magnetron-sputtered hard coatings [7]. The present paper reports on extended investigations using also the hollow cathode discharge arc evaporation and the cathodic arc evaporation in static and dynamic sample positions in laboratory and industrial equipment.
2.1. Samples
*Corresponding author. Tel.: +49 7171 100654; e-mail: femmail@compuse~e.com
10062126;
fax: +49 7171
02.57~8972/97/$17.00 0 1997 Elsevier Science S.A. All righlb reserved PII SO257-8972(97)00424-6
Mirror polished 2-mm thick high speed steel (HSS) platelets were used as substrate material. The different threedimensional (3D) profiles were realised by suitable mounting of these platelets. This technique allowed an easy characterisation of the coatings as a function of the position of the substrate areas after demounting. The following shapes were selected as 3D mode samples: U-groove of different depths, V-groove and V-wedge of different angles and, hence, of different depths (see Fig. 1). The upper width of the U-grooves and the V-grooves was 10 mm. The extension of the samples perpendicular to the drawing plane was 50 mm. 2.2. Coating deposition Because of the importance of a homogeneous coating process for many tribological - and also decorative applications, TiN was selected as coating material. It was deposited by various reactive PVD techniques, i.e. double magnetron (DM), unbalanced magnetron (UBM), cathodic arc deposition (CAD) and hollow cathode discharge arc evaporation (HCD). These deposition techniques are characterised as follows: The double magnetron is formed by a pair of opposed balanced magnetrons; both were powered
HA.
Jehn et a!. /Surface
and Coniings
but the model samples were faced to only one of them. The unbalanced magnetron has a plasma extended by an additional magnetic field towards the substrate. Cathodic arc deposition (solid source) and hollow cathode discharge arc evaporation (liquid source) are characterised especially by their high degree of ionisation of the vaporised atoms and the high energy of the particles even increased by a bias voltage. The samples were coated in static and dynamic (rotating) positions. Fig. 2 illustrates the geometrical ar-rangements in the laboratory and industrial coating devices. After thorough wet cieaning of the platelets in ultrasonic baths, the samples were composed and mounted in the deposition system and sputter-cleaned prior to the coating procedure. A thin Ti interlayer was first deposited to ensure good adhesion of the TiN coatings. The parameters of the coating deposition are summarised in Table 1. 2.3. Coating
Technology
94-95
(1997)
232-236
Schematic deposition principles static:
00
xl
dynamic: DM, CAD, HCD
DM, UBM, CAD, HCD
Industrial deposition principle
chnructerisation
The coatings were characterised for thickness, morphology and hardness as a function of the profile depth which is characterised as perpendicular distance from the outermost part of the profile (see Fig. 1). The thickness and morphology were determined by the calotest and scanning electron microscopy of fracture surfaces, respectively. The thin film thicknesses were normalised to the thickness of a plane sample positioned at the outermost part of the profile directed to the source. The hardness was characterised by depthsensing indentation measurements (Vickers pyramid) which were evaluated in terms of hardness equivalents [ 8 -101. The latter is an indenter-specific density of the deformation energy which is better suited for the characterisation of coating-substrate systems than the conventional hardness values. This method is particularly applicable to the characterisation of very thin films. In part the hardness was also characterised by the universal hardness (indentation depth under load) using a Knoop indentor (HUK). Other tests covered thickness by X-ray fluorescence analysis, surface roughness by laser stylus profilometry, chemical composition by glow discharge optical spectroscopy, colour as well as wear and friction, but in a less complete
Particle fluxes
..~
. . . . .
. ;;$
,
,2cm,
Plane
U-groove
i
/’ Wedge V-groove 11 Angle
Fig. 1. Model samples for 3D part coating studies.
II Flux source(s) Fig. 2. Schematic arrangement deposition.
x
Substrate(s)
of samples in static and dynamic coating
manner. The results shall not be discussed here in detail and are reported elsewhere [ 111.
3. Results and discussion 3.1. Coating
thickness
In Fig. 3a-c, the major results of the thickness measurements are summarised. The following general statements can be made. (i) A marked decrease of the coating thickness is noted for higher profile depths. This holds for the bottom of the Ugroove as well as the side wall of the U-groove and the Vgroove. For wedges a lower thickness is noted in the nearedge area due to material loss by sputtering processes. In the V-grooves, in contrast, the same sputtering processes cause no effective material loss. The dependencies plotted in Fig. 3a for coatings deposited in the double magnetron arrangement with static sample position reflect qualitatively the distribution in the other coating processes with static sample positions. The angle of incidence expectedly influences the absolute coating thickness also at the uppermost area. The coating thickness decreases with decreasing angle. -(ii) The characteristics of the different PVD processes also influence the thickness distribution on 3D samples. This is mainly caused by the different flux and energy distributions of the film-forming and modifying particles. Typical examples for these effects are shown in Fig. 3b using the bottom of the U-grooves and the 54”-V-groove with static deposition principle. A major characteristic of the plots is the stronger decrease in thickness with profile depth for magnetron sputtering (DM, UBM) values com-
234
HA. Jehn et al. / Sutfuce and Coatings Technology
94-S
(1997) 232-236
Table 1 Experimental
conditions UBM
HCD
CAD
CAD (ind.)
300 Ar’, 40 0.1
300 A?, 40 0.1
300 Ar’ 0.1
300 Ar-, Ti0.1
300 At-‘, Ti+ 0.1
5 x 10-3 9 x lo-? Ark& 300 -100 8
5 x 10-3
5 x 1o-3
5 x 1O-3
atmosphere Substrate temp. (“C) Substrate bias (V) Source-substrate distance (cm)
5 x 1o-3 2 x 10-Z Ar& 300 -100 5 20
W 200 -50 14 21 20
N, 400 -50 min 25
Deposition
AT/N? 460 -50 14 21 20
DM Static Preueatment Heating (“C) Ion etching (min) Ti interlayer (pm) Tii deposition Pressure (mbarj
time
Dynamic
240
55
120
DM, double magnetron, Leybold Z 700; WM, unbalanced magnetron, laboratory system; HCD, hollow cathode discharge, semi-industrial IPMT; CAD (irk), cathodic arc deposition, PVT 840.
pared with the arc techniques (HCD, CAD). This can be attributed to the higher degree of ionisation of the metal vapour in HCD and CAD which results in a better depth efficiency. This trend found with U-groove and 54’-Vgroove samples also holds for the other V-groove and wedge samples. An exception is the 30”-V-groove which shows an almost constant film thickness along the profile depth (Fig. 3b, lower left diagram). It is assumed that this relatively high and constant thickness is caused by the enhanced sputtering efficiency for low-angle ion incidence. This effect is more pronounced for UBM than for balanced sputtering (DM). In HCD and CAD this effect is not observed because the denser plasmas in those arrangements follow more strictly the shape of the surface and result in an incidence more perpendicular to the surface. (iii) The effect of sample movement (dynamic deposition) is illustrated in Fig. 3c, showing the results for the slightly curved motion in front of the inner cathode of the double magnetron arrangement and for the twofold rotation of the industrial two-target cathodic arc deposition device. The results show a stronger decrease of the thickness with increasing profile depths due to partial shadowing of the deeper groove areas when the samples are not directly oriented to the target. This effect becomes more pronounced with deeper grooves (higher aspect ratio). In orienting measurements the influence of the source-to-substrate distance, the working gas pressure and the bias voltage were studied. The trends (iv) and (v) have been observed. (iv) For larger source-to-substrate distances a relatively lower deposition rate exists. The decrease of the coating thickness with increasing profile depth for U- and Vgrooves is similar to samples mounted in a smaller distances. (v) An increased working gas pressure results in a markedly higher film thickness in the outer parts of the grooves.
systems, GFE-
This results from increased scattering effects in the transport space. Simultaneously, the deeper areas show a reduced thickness when compared with the deposition at lower pressures. 3.2. Morphology The morphology of PVD coatings in relation to the phenomena considered in this study depends strongly on the angle of incidence, the energy of the impinging atoms/ ions and the deposition rate. Fig. 4 shows the morphology of the TiN coatings deposited on different wedges together with the film on a plane substrate. For perpendicular incidence in static deposition a perpendicular orientation of the columnar crystallites is built up, and other angles of incidence result in a crystal growth directed towards the source. But a maximum deviation from the perpendicular growth is found even for a 30”~wedge. The comparison of the structure formed on the 30”-wedge in the double magnetron with the unbalanced magnetron deposition shows a much more perpendicular growth in the latter case due to the more intense ion bombardment of the growing film. The continuously varying incidence on rotating substrates (dynamic deposition) also yields a much less columnar and almost perpendicularly oriented structure. This holds especially for the twofold rotation in the industrial coating device. Another fact has to be noted, namely, the morphology in the very near-edge region of the wedge samples is almost featureless. This is attributed to the increased ion flux due to the enhanced electrical field in the vicinity of the edges. Details of this effect are described elsewhere [ 121. 3.3. Hardness The hardness of the coatings deposited on the side-
H.A. John et al. / Suq?zce rind Coatings Techno!ogy 94-95
Double magnetron,
static deposition
235
(1997) 232-236
DM, stat.
UBM, stat.
DM, dyn.
90” wedge
90” wedge
plane
30” wedge
30” wedge
30” wedge
Profile depth [mm]
b
Processes, U-groove:
static deposition side walls, depth 20 mm
bottom
mj
--2-pm Fig. 4. Coating morphology
0
5
10
15
10
20
15
coating conditions.
wall (U-groove) and the differently shaped V-grooves and wedges, in general, is lower than that of the reference plane; in part even lower than the substrate material. Exceptions are the dynamically deposited CAD coatings. This reflects the difficulties to deposit hard coatings on com-plexshaped substrates and especially in grooves by static magnetron sputtering. These relations shall therefore not be discussed in more detail. However, in the near-edge regions of the dynamic CAD coatings, constant and even increasing HE values are measured. This effect can in part be related to the already mentioned increased ion flux. A surprising effect, however, was found at the bottom of the U-grooves with sputtered films. Nearly constant HE values were found for all profile depths (Fig. 5), an effect which is not yet understood.
20
Profile de;th [im] C
for different
Processes, dynamic deposition CAD DM U-aroove. bottom
-
3.4. Other properties
I
,
0
5
10
15 20 25
0
5
10
1.5 20 25
Profile depth [mm] Fig. 3. Coating thickness distri&tion on model samples. (a) Effect of sample shape; (b) effect of PVD process; (c) effect of sample movement.
As already mentioned, the colour of the films was also determined. The golden colour of the sputtered TiN coatings changes into greyish or blackish for deeper groove and wall areas of magnetron-coated samples, indicating a change of composition and morphology. This was not found for CAD because that deposition process is less sensitive to variations in the process parameters such as nitrogen gas pressure and source-to-substrate distance.
236
HA. Jehn et al. /Su$ace
nnn,
U-aroove
and Conrings Terhnology
-0-
(1997) 232-236
Acknowledgements
(bottom)
LUU
t
94-95
These investigations were in part funded by the German Federal Ministry of Economic Affairs under contract number AiF 9138. This support is gratefully acknowledged.
5~10~ mbar, stat.
mpo2 ;;;lOOI
_^ SUI
l’
-@-~55x10~
,
0
References
mbar, dyn.
1 20
Fig. 5. Hardness of TiN coatings on 3D model parts.
4. Conclusion Differently shaped model samples were coated by different reactive PVD processes in laboratory and industrial equipment (double magnetron sputtering, unbalanced magnetron sputtering, hollow cathodic discharge evaporation and cathodic arc deposition) with and without sample motion. U-groove, V-groove and wedges with different angles and depths were selected as model samples. Coating thickness, morphology and hardness were measured as a function of the geometry and profile depth and compared to the coating deposited on a flat sample. The properties of the coatings can be explained by the influence of the different process parameters (PVD method, substrate-to-source orientation and distance, shadowing and electrical field effects). The use of demountable model samples and the applied measurement technique allow statements to be made on the realistic coating behaviour deduced from model experiments.
111B.O.
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