Development of tribological PVD coatings

Escola PolitécnicaUniversidade de São Paulo

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Development of tribological PVD coatings

Roberto M. Souza .

Laboratório de Fenômenos de Superfície

Departamento de Engenharia Mecânica

Escola Politécnica da Universidade de São Paulo

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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

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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 ]


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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

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– 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




Residual Stresses

Adhesion

Evaluation Modeling

Experimental

Analytical


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.

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• Conventional MS Davis’ model Unbalanced MS Davis’ model

[Y. Pauleau, Vacuum 61, 2001, 175-181]


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Residual Stresses




Residual Stresses

Adhesion

Evaluation Modeling

Experimental

Analytical


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

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• Confirm literature data that compressive film residual stresses may be beneficial as long as film/substrate adhesion is not impaired



Second set of TiN specimens

Gradient stresses


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Residual Stresses

Adhesion

Evaluation Modeling

Experimental

Analytical


Material Processing


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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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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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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


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Residual Stresses

Adhesion

Evaluation Modeling

Experimental

Analytical


Material Processing


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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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33


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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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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35


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


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Residual Stresses

Adhesion

Evaluation Modeling

Experimental

Analytical


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.



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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• 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