development of tribological pvd coatings
DESCRIPTION
Trabalho apresentado pelo prof. Roberto M. Souza (LFS-EPUSP) no 64o Congresso internacional da ABM, em Belo Horizonte (MG), em julho.TRANSCRIPT
Escola PolitécnicaUniversidade de São Paulo
Development of tribological PVD coatings
Roberto M. Souza .
Laboratório de Fenômenos de Superfície
Departamento de Engenharia Mecânica
Escola Politécnica da Universidade de São Paulo
Escola PolitécnicaUniversidade de São Paulo
Escola PolitécnicaUniversidade de São Paulo
Escola PolitécnicaUniversidade de São Paulo
Outline
• Overview – Development of PVD coatings
– Ideas currently in use - Examples
• Thin film development at the Surface Phenomena Laboratory
– Measurement, tribological evaluation, film processing
– Example – Film residual stresses
4
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PVD• Global value of PVD industry
– Data from 2007
– Predicted annual
growth rate for
the next 5
years:
11 % per year
5
[http://www.bccresearch.com/report/MFG015C.html]
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Development of PVD Coatings• Book chapter: O. Salas, J. Oseguera “Megatendencia:
Ingeniería de Superficies”– Question asked to a number of specialists: “… currently,
surface engineering pushes or pulls the market?”
6
– Possible interpretation of the question:
What question occurs more frequently?
Developer to industry: I have developed this coating, would you test it for me?
Industry to developer: I need a coating with the following properties, would you develop one for me?
– No clear trend in the answers
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Thin film development
7
[Donnet & Erdemir Surf. Coat. Technol. v.257, 2004]
• This presentation
– PVD
– Mostly hard coatings
• Recent developments
– Drive or driven by industrial needs?
• Development in three main areas
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Examples – Materials and Structures
• Adaptive coatings– Merging multiple complementary
solid lubricants in a nanocomposite coating
– Continuous response of the contact surface to the surroundings
• Load
• Sliding speed
• Environment
• Temperature
8[Muratore & Voevodin Ann. Rev. Mat. Res. 39 (2009) 297-324]
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Examples - Processing• Pulsed Magnetron Sputtering (PMS)
– Use for the deposition of highly insulating materials– Reduction of arcing events
9
0 50 100 150
-500
-400
-300
-200
-100
0
100
Tar
get v
olta
ge, V
Time, microseconds
Al2O3 films
DC reactive sputtering Pulsed reactive sputtering
[P.J. Kelly et al. Surf Coat Technol 86-87 (1996) 28-32][P.J. Kelly and D.R. Arnell, Vacuum 56 (2000) 159-172]
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Side View
Top View
Hiden electrostatic quadrupole plasma mass spectrometer (EQP)Al Cr
10
Examples - Processing• Pulsed Magnetron Sputtering (PMS)
– Plasma monitoring during
the deposition of
Cr1-xAlxN coatings for Al die
casting applications• Ion flux
• Ion energy
[Courtesy: J.J. Moore, ACSEL, Colorado School of Mines ]
Escola PolitécnicaUniversidade de São Paulo
0 20 40 60 80 100 120 140 160 1800.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
3.0x106
29N2
+
Pulsing both targets synchronously Pulsing both targets asynchronous Only pulsing Al target
SE
M C
/S
Ion Energy (eV)
(a)
[J. Lin et al., Surface and Coatings Technology 201 (2007) 4640]
Examples - Processing
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
38( Ar+)
40( Ar+)
42( N3
+)
56( N4
+)
54( Cr+)
53( Cr+)
52( Cr+)
50( Cr+)
36( Ar+)
29( N2
+)
28( N2
+)
26.7( Al+)
18( H2O)
14( N+)
Inte
nsi
ty [
arb
.un
its]
AMU
66( CrN+)
68( CrO+)
• Pulsed Magnetron Sputtering (PMS)– Ion energy and ion flux
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Examples - Processing• High Power Pulse Magnetron Sputtering – HPPMS (also known as High Power Impulse Magnetron Sputtering – HIPIMS)
– Highly ionized flux of sputtered material instead of large amount of neutrals
– Low deposition rates
12
• Modulated Pulse Power – MPP– Advantages of HPPMS– High deposition rates
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Examples - Processing• Modulated Pulse Power – MPP
13
0 20 40 60 80 1000.0
2.0x105
4.0x105
6.0x105
8.0x105
1.0x106
0 20 40 60 80 1000.0
2.0x105
Continuous dc discharge Pulsed dc discharge MPP discharge
Inte
nsity
[CPS
]
Ion Energy [eV]
52Cr+
Pave
=1.2 kW
5 mTorr
Continuous dc discharge Pulsed dc discharge MPP discharge
Inte
nsity
[CPS
]
Ion Energy [eV]
52Cr+
Pave
=1.2 kW
5 mTorr
0.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
3.0x106
MPP Pulsed DC
Inte
grat
ed C
r+ fl
ux
Continuous DC
[Courtesy: J.J. Moore, ACSEL, Colorado School of Mines ]
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Examples - Materials• Materials – Nitrides and carbonitrides
– TiN, TiCN, CrN, ZrN, TaN
14
– TiAlN, TiSiN, TiAlCN, CrAlN, TiCuN, TiNbN, TiHfN, TiVN, TiZrN, TiMoN
– TiAlSiCrN
– TiAlVN, TiCrAlN, ZrCrAlN, TiAlNbN
– Drive or driven by industrial needs?
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Surface Phenomena Laboratory
• Tribological (wear, friction) behavior of thin films
Thin Film Characteristics
Hardness Fracture Toughness
Residual Stresses
Adhesion
Evaluation Modeling
Experimental
Analytical
Wear x characteristic
Material Processing
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Residual Stresses
• Tribological (wear, friction) behavior of thin films
Thin Film Characteristics
Hardness Fracture Toughness
Residual Stresses
Adhesion
Evaluation Modeling
Experimental
Analytical
Wear x characteristic
Material Processing
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Residual Stresses in Thin Films• Several reviews are available in the literature. Usually:
– Effects of thin film stresses– Measurement techniques– Sources
17
• Sources– Classification. Different views in the literature
• Intrinsic: During deposition• Extrinsic: After the film growth step is concluded
In the contents
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[J.A. Thornton, D.W. Hoffman, Thin Solid Films, 171 (1989) 5-31.]
Residual Stresses in Thin Films• Extrinsic stresses – In general,
• Intrinsic stresses – Commonly due to defects generated during deposition
• Effect of intrinsic and extrinsic stresses– Ratio between deposition and
melting temperature Td / Tm
– vs. Adatom mobility18
PVD CVD
TTE
dSubstrateTFilmTFilm
Filmthermal
1
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Residual Stresses in Thin Films• Physical Vapor Deposition (PVD) films:
– Different techniques developed to achieve denser films, which have better tribological properties
– Effect of ion bombardment – Structure zone models
19
Td/Tm
Evaporation
[B.A. Movchan, A.V. Demchishin, Phys. Met. Metallogr., 28 (1969) 83-
90.]
Close-fieldUnbalanced MS
[P.J. Kelly, R.D. Arnell, Vacuum, 56 (2000) 159-172.]
Td/Tm
Sputtering
[J.A. Thornton, Ann. Rev. Mater. Sci.,7 (1977) 239-260.]
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Residual Stresses in Thin Films• PVD films:
– Models to determine intrinsic stresses• Windischmann (1987,1992): Stresses
are directly proportional to the flux of energetic particles arriving on the substrate and to the square root of their kinetic energy.
• Davies (1993): Thermal spikes to reduce stress by causing displacement of the implanted atoms.
20
• Conventional MS Davis’ model Unbalanced MS Davis’ model
[Y. Pauleau, Vacuum 61, 2001, 175-181]
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Residual Stresses
• Tribological (wear, friction) behavior of thin films
Thin Film Characteristics
Hardness Fracture Toughness
Residual Stresses
Adhesion
Evaluation Modeling
Experimental
Analytical
Wear x characteristic
Material Processing
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First set of TiN specimens
Pulsed Magnetron Sputtering
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First Set of TiN Specimens• Set of specimens prepared with or without target pulsing (PMS)
– Residual stresses increased with applied bias and with PMS
23
-100 -50 0-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1-250 -200 -150 -100 -50 0
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
Res
idu
al s
tres
s (G
Pa)
Bias voltage (V)
DC specimens: D0, D50, D100 PF P50 PG
-12 -11 -10 -9 -8 -7 -6 -5 -4 -30.05
0.10
0.15
0.20
0.25
0.30
b
k c (x
10-1
4 m2 /N
)
Residual Stress (GPa)
DC0 and DC100 PF P50 PG
[R.C. Cozza et al. Surf. Coat. Technol. 201 (2006) 4242-4246][M. Benegra et al. Thin Solid Films 494 (2006) 146-150]
• Micro-scale abrasion tests– Overall trend of wear reduction with the increase in film stresses
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First Set of TiN Specimens• However, film debonding if
the film stresses were too compressive
24
• Confirm literature data that compressive film residual stresses may be beneficial as long as film/substrate adhesion is not impaired
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Second set of TiN specimens
Gradient stresses
Escola PolitécnicaUniversidade de São Paulo
Surface Phenomena Laboratory
• Tribological (wear, friction) behavior of thin films
Thin Film Characteristics
Hardness Fracture Toughness
Residual Stresses
Adhesion
Evaluation Modeling
Experimental
Analytical
Wear x characteristic
Material Processing
Escola PolitécnicaUniversidade de São Paulo
Second set of TiN specimens• Main idea: Prepare films grading
the residual stress level – Control of deposition substrate bias
27
Reduce wear
Improve adhesion
[E. Uhlman & K. Klein, Surf. Coat. Technol. 131 (2000)]
– Stress graduation obtained
based on the control of the
pressure during the deposition
• Previous works in the literature– Fischer and Oettel, Surf. Coat. Technol.
97 (1997)
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Second set of TiN specimens• Idea poses two questions
– Question 1: How to measure the stress gradient• TiN films obtained in hybrid reactor after plasma nitriding
– Triode magnetron sputtering deposition– D2 substrates– M2 substrates– Substrate bias increasing, decreasing or constant
28
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Second set of TiN specimens
29
Specimen Layer Time (min) Bias (V)
G1D2
1 45 -20
2 45 -40
3 45 -100
4 45 -150
5 45 -200
G2D2
1 45 -200
2 45 -150
3 45 -100
4 45 -40
5 45 -20
S1 1 120 -20
S2 1 120 -40
S3 1 120 -100
S4 1 120 -150
S5 1 120 -200
Increasing bias
Decreasing bias
Constant bias
• Stress measurement – D2 substrates
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Second set of TiN specimens
30
Specimen Layer Time (min) Bias (V)
G3M2
1 45 -20
2 45 -40
3 45 -80
4 45 -100
G4M2
1 45 -100
2 45 -80
3 45 -40
4 45 -20
Increasing bias
Decreasing bias
• Stress measurement – M2 substrates
Escola PolitécnicaUniversidade de São Paulo
Surface Phenomena Laboratory
• Tribological (wear, friction) behavior of thin films
Thin Film Characteristics
Hardness Fracture Toughness
Residual Stresses
Adhesion
Evaluation Modeling
Experimental
Analytical
Wear x characteristic
Material Processing
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Second set of TiN specimens
32
• Stress measurement – X-ray diffraction with grazing
incident angle
– Results of “single layer”
thin films: S1 to S5
– Agreement with literature
0 -50 -100 -150 -200
-2
-4
-6
-8
Res
idua
l str
ess
(GPa
)
Bias voltage (V)
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Second set of TiN specimens
33
• Stress measurement – X-ray diffraction with grazing
incident angle– How to measure the gradient?– Idea: H. Dolle, J. Appl. Cryst. 1979
mean value of residual stress over
a depth x
tx
t t
t
t
t
t
t
t
t
xxxxx
dxe
dxedxedxedxedxe
0
/
0
/5
/4
/3
/2
/1
1 2
1
3
2
4
3 4)(
1
2
34 5
0.00 0.42 0.84 1.26 1.68 2.100.0
0.2
0.4
0.6
0.8
1.0
Dif
ract
ed I
nten
sity
Depth penetration m)
I para =1.5 I para =2.5 I para =3.5 I para =4.5 I para =6 I para =8 I para =10
tx
tx
x
dxe
dxe
0
/
0
/
)(
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Second set of TiN specimens
34
• Stress measurement – X-ray diffraction with grazing
incident angle – D2 substrates– Use values of the single layers
to calculate value measured
with X-ray diffraction
tx
t t
t
t
t
t
t
t
t
xxxxx
dxe
dxedxedxedxedxe
0
/
0
/5
/4
/3
/2
/1
1 2
1
3
2
4
3 4)(
1,2,3,4,5
0 2 4 6 8 100
-1
-2
-3
-4
-5
-6
Res
idua
l Str
ess
(GP
a)Angle of incidence (deg)
G1D2 (experimental) G1D2 (model) G2D2 (experimental) G2D2 (model)
a)
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Second set of TiN specimens
35
• Stress measurement – X-ray diffraction with grazing
incident angle – M2 substrates– Use values of the single layers
to calculate value measured
with X-ray diffraction
tx
t t
t
t
t
t
t
xxxx
dxe
dxedxedxedxe
0
/
0
/4
/3
/2
/1
1 2
1
3
2 3)(
1,2,3,
4
0 2 4 6 8 100
-1
-2
-3
-4
-5
-6
Res
idua
l Str
ess
(GP
a)Angle of incidence (deg)
G3M2 (experimental) G3M2 (model) G4M2 (experimental) G4M2 (model)
b)
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Second set of TiN specimens• Idea poses two questions
– Question 2: How to evaluate the tribological behavior
• Pin-on-disk testing– High contact pressure– Low contact pressure
36
Escola PolitécnicaUniversidade de São Paulo
Surface Phenomena Laboratory
• Tribological (wear, friction) behavior of thin films
Thin Film Characteristics
Hardness Fracture Toughness
Residual Stresses
Adhesion
Evaluation Modeling
Experimental
Analytical
Wear x characteristic
Material Processing
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Second set of TiN specimens• Tribological behavior – M2 substrates
38
– Increasing bias
– Decreasing bias
– Constant bias
0 20 40 60 80 100 120 140 1600
20
40
60
80
100
120
Epaisseur (m)
Pol
aris
atio
n (V
)
Temps (minutes)
Croiss Const Decroiss
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
– Differences in curvature: initial bias determined the curvature even if the average bias value was equal
Increasing Const. Decr.
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Ensaios de Deslizamento – Pression Alta (2)
• Tribological behavior – Sliding test at high contact pressure– Pin: Steel, R = 5 mm– Track length = 10 mm– Frequence: 10 mHz (v = 0.2 mm/s)
• F x t (Pressão x t):
1 cycle– 200 à 400 N (2,8 à 3,5 GPa)– 150 à 350 N (1,7 à 3,3 GPa)
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Second set of TiN specimens• Tribological behavior
– Conventional scratch test – Critical load for adhesive failure• Increasing bias: 16.2 ± 1.8 N• Decreasing bias: 3.1 ± 0.2 N
– “Non-conventional” scratch test: Steel spherical stylus (R = 5 mm),
increasing normal load from 150 to 400 N (Nominal Hertz Pmax from
1.7 to 3.4 GPa)
40
Constant Increasing Decreasing
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Second set of TiN specimens• Tribological behavior – Sliding test at low contact pressure– Pin: Steel, R = 100 mm– Track length = 3 mm– Frequence: 100 mHz (v = 0.6 mm/s)– F x t (P. Max Hertz x t):
150 cycles
50 N (0,24 GPa – PMax Hertz)
41
Hole (trou)
Rupture
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Second set of TiN specimens• Optical spectroscopy
42
– 594 sectional profiles– Average of profiles
Increasing bias
Constant bias
Decreasing bias10
0 nm
100
nm10
0 nm
Increasing
Track width
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Second set of TiN specimens
• Friction coefficient: Results similar to those in the literature for TiN – High friction coefficient values– High values from the first
cycles– All films behaved similarly
43
0 5 10 15 20 250,0
0,2
0,4
0,6
0,8
1,0
Coe
ffici
ent d
e F
rotte
men
t
Cycles
Constante - trou
0 5 10 15 20 250,0
0,2
0,4
0,6
0,8
1,0
Coe
ffici
ent d
e F
rotte
men
t
Cycles
Decroiss. - trou
0 5 10 15 20 250,0
0,2
0,4
0,6
0,8
1,0
Coe
ffici
ent d
e F
rotte
men
t
Cycles
Croissante - trou
0 5 10 15 20 250,0
0,2
0,4
0,6
0,8
1,0 Constante - Rupture
Coe
ffici
ent d
e F
rotte
men
t
Cycles
0 5 10 15 20 250,0
0,2
0,4
0,6
0,8
1,0 Decroiss. - Rupture
Coe
ffici
ent d
e F
rotte
men
t
Cycles
0 5 10 15 20 250,0
0,2
0,4
0,6
0,8
1,0 Croissante - Rupture
Coe
ffici
ent d
e F
rotte
men
t
Cycles
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Second set of TiN specimens• This study has shown
– Quick formation of a third body layer at the pin surface and high friction coefficient
– Gradual oxidation of the specimen surface
– Negligible wear of the specimens– Similar behavior in all cases
44
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Concluding Remarks• Discuss, with examples, some routes for the
development of PVD coatings
• Present an overall organization of the study of the tribological behavior of thin films – driven by the market– Emphasize necessity of accurate measurement and
the importance of the choice in tribological testing
45
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Acknowledgements• FAPESP, CNPq, CAPES• Research groups – Actual experimental analysis
– LFS – Esc. Politécnica USP – ACSEL – Colorado School of Mines, USA– TMI – INSA-Lyon, France– IPEN– Inst. Física – USP– CNEA, Argentina
• Plus valuable discussions with many other groups
46
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Second set of TiN specimens• Tribological behavior – Tensile testing
– In theory, provides quantitative results in terms of film fracture toughness and film/substrate adhesion
48
F
F
-0,01 0,00 0,01 0,02 0,03 0,040
500
1000
1500
2000
2500
TiN sur M2 - Jan, fev 2008
Con
trai
nte
- F
/Ao
(MP
a)
Déformation - L/Lo
* 2 m UDESC * 1 m UDESC #1 * 1 m UDESC #2 + 1.4 m Croiss. #1 + 1.4 m Croiss. #2 + 1.4 m Decroiss. #1 + 1.4 m Decroiss. #1 + 1.4 m Bias = #1 + 1.4 m Bias = #2
(*) Couche a fissuré(+) Couche n'a pas fissuré
Catastrophic failure before significant plastic deformation of the substrateFilm fracture was not observed
during the test Impossible to compare the deposition conditions
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Second set of TiN specimens• Evolution of specimen surface throughout the cycles
49
« particles »Third body
oxidationFirst body
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Second set of TiN specimens• Fraction of “particles” and oxidized area
50
0 20 40 60 80 100 120 140 1600
5
10
15
20
25
30
35
40TrouRupture
Début - Constante Fin - Constante Fin - Constante Début - Decroiss. Début - Croiss.
% "
Pha
se"
Cycles
Début - Constante Fin - Constante Début - Decroiss. Début - Croiss. Fin - Croiss. Fin - Croiss.
Trou
Rupture0 20 40 60 80 100 120 140 160
0
5
10
15
20
25
30
35
40
% "
Ph
ase
"Cycles
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Second set of TiN specimens• FEG: Field Emmission Gun - Specimen
51
Increasing bias, hole
– Observation of iron oxyde on track surface: Free and agglomarated particles
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Second set of TiN specimens• Pin surface
52
Increasing bias
Constant bias
Rupture Hole
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Second set of TiN specimens• Scanning electron microscopy- Pin
53
Pol. Croissante - Trou