26/09/2017

1

Fretting wear of low current (DC)

electrical contacts: quantification

of electrical endurance

S. Fouvry1, J. Laporte1, O. Perrinet1, P. Jedrzejczyk1,

O. Graton1, R. Enquebecq1,3, O. Alquier2, J. Sautel3

1 Laboratoire de Tribologie et Dynamique des Systèmes, Ecole Centrale de Lyon, France 2 PSA, Vélizy - France 3 Radiall,Voreppe, France

1

(contact : siegfried.fouvry@ec-lyon.fr)

2

Fretting Group @ LTDS

Fretting Wear, Fretting Fatigue

Fretting & Electrical Contacts

Plateforme 2DFDurabilité, Fretting & Fatigue

Plateforme numériqueBureaux des chercheur de la thématiquefretting

Lyon

Ecole Centrale de Lyon

26/09/2017

2

Industrial context

Micro-displacements

Fretting Wear

3/19

• Fretting solicitations

• Contact wear

• Loss of electrical conduction

0,0001

0,001

0,01

0,1

1

10

0 5000000 10000000 15000000 20000000 25000000

NUMBER OF CYCLES N

ELE

CTR

ICA

L R

ESIS

TA

NC

E R

[

] Electrical Failure

Threshold resistance

Nc: ECR (electrical contact resistance endurance)

Nc

B. H. Chudnovsky, Proc. 48th IEEE Holm, (2002), 140–150.

R. S. Timsit, IEICE Transactions on Electronics 88 (8), (2005)

Electrical Contact Resistance : ECR

N. Ben Jemaa, 23th ICEC, 2006, 215-219

M. Antler, IEEE Transactions 7, 1984, 363-369

S. Noël et al. Wear 301, 2013, 551-561

J. W. McBride, proc. 52th IEEE conf., 2006, 170-180.

1. Experimental Simulation

2. ECR endurance versus sliding amplitude

3. Fretting surface damages & ECR behaviour

4. ECR & Friction energy density concept

5. Complex Fretting-Reciprocating slidings

6. ECR versus Coatings properties

7. Conclusions

TOPICS

26/09/2017

3

Experimental setup

Crossed cylinders (90°)

r = 2.35 mm

2.aHertz

Cross Cylinder configuration

Q(N)

(µm)

displacementTan

gentialfo

rce

*Q : tangential

force

amplitude

)J(Ed

: dissipated

energy: displacement amplitude*

02

2 S

Fretting Loop

*( )Q N

( )µm

Fretting Log

Q(N)

(µm) displacement

Tangential force

*Q

Fretting cycle

δ*

δ0

displacement amplitude (test compliance dependent)

δ0 : Sliding amplitude (=> δ when Q=0)

Ed (J) friction energy

5

6

Fretting Connector 1

Fretting : δ* : 1 – 30 µm

Temperature : 20 -200°C

Frequency: 30 – 500 hz

Humidity (salt) : 10 – 90% RH

Fretting Connector 2

Fretting : δ* : 1 – 30 µm

Temperature : 20 -200°C

Frequency: 30 – 500 hz

Humidity (salt) : 10 – 90% RH

Gazes (doping) : H2S & S02

Fretting Connector 3

Fretting : δ* : 1 – 30 µm

Reciprocating : D : 0.1 to 10 mm

Temperature : 20 -200°C

Frequency: 30 – 500 hz

Humidity (salt) : 10 – 90% RH

DC micro fretting test platform @ LTDS (Ecole Centrale de Lyon)

26/09/2017

4

elec

tric

al r

esis

tan

ce R

(

)

Rmin

Nc (electrical

endurance)

fretting cycles

DRc=0.004 Electrical failure when:

DR> DRc=0.004

Definition of the electrical failure criterion

Four point method Stabilized current : I = 0.005 A

Normal force P=3N

Displacement *

7/19

S. Hannel et al, Wear 249, 2001, 761-770 W. Ren, et al. Tribology International 83,(2015), 1-11

Flowers G.T et al. Proc. of the 51st IEEE Holm Conf., 2005, 82-88

Malucci, R.D., Proc. of the 49th IEEE Holm Conf., 2003, 1-15

Studied materials and test conditions

Noble

CuSn4 (substrate)

Ni 2 µm

CuSn4 (substrate)

Ni 2 µm

e (µm) Au coatings

CuSn4 (substrate)

Ni

CuSn4 (substrate)

Ni

Ag coatings

CuSn4 (substrate)

Ni

CuSn4 (substrate)

Ni

Sn coatings

Gold Silver Tin Semi-Noble Non Noble

Sn coatings Ag coatings Au coatings

Applied test conditions: Temperature: 25°C Relative humidity: 10% Frequency: 30Hz Normal force & δ : varying

crossed cylinders

90°

r = 2.35 mm

2.aHertz

Sphere/Plane If P= 3N

aHertz=43µm & pH, max=772MPa

Electrodeposition process

e (µm)

8

26/09/2017

5

Reciprocating 1

*

a

e

Q

2δ*

a

reciprocating

Basics of fretting contact : sliding condition

tan

gen

tial

fo

rce

amp

litu

de,

Q*

displacement amplitude, *

Closed cycle

stick zone

sliding zone

Partial Slip

Q

20

Q*,*

P

normal force

displacement (µm)

tangential force Q (N)

transition amplitude, *t

full sliding

2*

Q

20

Q*=µ.P

2δ*

a

Gross Slip

open cycle

9

10

Partial slip (infinite ECR endurance)

undamagedstick zone(metal/metal)

wear in externalsliding zone

70 µm

Gross slip (finite ECR endurance)

- generalizedwear of the interface.- formation of an completeoxide debris layer.

0.000

0.002

0.004

0.006

0.008

0.010

0 1000 2000 3000 4000 5000

Nc

fretting cycles, N

* 7 µm

R ()

100 µm

* 4 µm

ΔR=ΔRth = 4 mΩ

sliding condition & Electrical contact resistance evolution

(Sn/Sn (e= 1.3 µm); P= 3N, f= 30 Hz, RH=10%, T=25°C)

“Fretting mechanical criterion” If δ* < δt (PS/GS transition) => inner stick metal zone => R low & stable (infinite endurance) If δ* > δt (PS/GS transition) => full sliding => Wear => R rises (finite endurance)

0.0001

0.001

0.01

0.1

1

10

100

1000

0 1 2 3 4 5 6 7 8 9 10

R (Ω)

partial slip

gross slip

displacement amplitude, δ* ( µm)

4 t µm

-0.8

-0.4

0

0.4

0.8

-6 -4 -2 0 2 4 6

δ (µm)

Q*/P

-0.8

-0.4

0

0.4

0.8

-6 -4 -2 0 2 4 6

δ (µm)

Q*/P

N = 10000 cycles

S. Hannel et al. Wear 249(9), 2001

26/09/2017

6

11

Correlation between fretting sliding condition and ECR behaviour

displacement amplitude, *

Stick zone

sliding zone

Partial Slip

Q Q*,*

R()

time (fretting cycle)

low & stable ECR

Infinite endurance

full sliding

Q

2δ*

a

Gross Slip

t

Q*,*

R()

time (fretting cycle)

finite endurance

ECR increase

tangential force

amplitude Q*

1.0

10

100

1000

Ag/Ag Au/Au Sn/Sn

Fretting cycles

Ele

ctr

ical c

onta

ct

resis

tance (

10

-3

)

0. 1

101 102 103 104 105 106 107 100

Sn/Sn

Ag/Ag

Au/Au

Comparison between Noble & non Non noble coating

Non noble : very fast decay

Applied test conditions: Temperature: 25°C Relative humidity: 10% Frequency: 30Hz Normal Force : 3 N Displacement : 8 µm Thickness coat. : 1.3 µm

Noble & semi noble : Delay before EC failure !

GT GP

Rc Rc

*< t *> t t

GT GP

Rc

Rc

*< t *> t t

Rc When non noble substract reached: ECR failure !

Wear (delay)

Non noble (Sn alloy)

Noble (Au & Ag)

12 S. Hannel et al. Wear 249(9), 2001

26/09/2017

7

2. Quantification of Nc (Electrical Contact Endurance) versus displacement & sliding amplitude ?

13

0

5

10

15

20

25

30

1 100 10000 1000000 1E+08

t_Au= 5µm

Finite endurance Domain (GS)

Infinite endurance Domain (PS)

Ap

plie

d d

isp

lace

men

t am

plit

ud

e

(µ

m)

fretting cycles, Nc (ΔR>4mΩ)

Au/Au interface

Electrical Endurances a function of the applied displacement amplitude

Asymptotic decreasing of NC (DRc=0.004 threshold): the larger the displacement the smaller the ECR endurance Nc

Applied test conditions: Temperature: 25°C Relative humidity: 10% Frequency: 30Hz Normal Force : 3 N Thickness coat. : 1.3 µm

14

26/09/2017

8

Quantification of the electrical endurance Curve : ”Fatigue like” approach :

perfect correlation between experiments and the exponential formulation (only 3 variables : δt , n, Ncδ

0

5

10

15

20

25

30

1 100 10000 1000000 1E+08 1E+10

fretting cycles, Nc (ΔR>4mΩ)

app

lied

dis

pla

cem

ent

amp

litu

de:

*

(µm

) n

t

NcNc

)(

*

y = -3.1898x + 16.748

R²= 0.9904

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

ln(N

c)

application to Au/Au interface

)ln( *

t

B

-n

BnNc t )ln()ln( *

With n = 3.18, B = 16.8 and µmt 5

Power law n

t

NcNc

)(

*

exp(B)

1µm) ( *

twhenNcNc

15 S. Fouvry et al. Wear 271 (9–10), (2011)

Comparison between coatings

- Small difference between δt transitions - Large difference between non noble Sn and noble Au&Ag ECR endurances - All the ECR endurance can be formalised using a simple power law function

Applied test conditions: Temperature: 25°C Relative humidity: 10% Frequency: 30Hz Normal Force : 3 N Thickness coat. : 1.3 µm

16 S. Fouvry et al. Wear 271 (9–10), (2011)

26/09/2017

9

Sliding amplitude formulation

The measured displacement depends on the test compliance => Results affected by the test signature !

measured δ (± µm)

real contact displ. δC (± µm)

test apparatus accommodation δA = Q x CA

ACAC CQ

δA : tangential test apparatus accommodation CA : test apparatus compliance

310 410 510 610 710 810 910 1010

Nc

0

5

10

15

20

25

30

1110

n

NcNc

)( 0

0 (±µm)

“power law function”

Ag/Ag Q(N)

(µm) displacement

Tangential force

*Q

δ*

δ0

δ0 : Sliding amplitude (=> δ when Q=0)

t *0

17 S. Fouvry et al. 58th IEEE Holm , 2012, 191-203

18

What about herogeneous interfaces ?

0

2

4

6

8

10

12

14

16

18

100 1000 10000 100000 1000000 10000000 100000000

fretting cycles, Nc

x10 /30

0 ( )µm

4

1.90

2.05 10Nc

5

20

2.03 10Nc

Ag/Ag

Sn/Sn

Ag/Sn7

2.80

4.74 10Nc

Ag/Sn still controlled by noble/noble fretting wear response (ECR failure is delayed by the coating wear) : But the formation of abrasive Sn oxides accelarate the Ag surface wear => mitigate benefit of Ag (only x 10 compared to Sn/Sn !)

O. Perrinet et al., ICEC 2014, p. 114-119.

26/09/2017

10

3. Correlation between fretting damage (surface wear & oxide debris)

& Electrical behavior

19

Study of the endurance degradation for homogeneous Ag/Ag interface

0

0.002

0.004

0.006

0.008

0.01

0 20000 40000 60000 80000 100000

Ré

sis

tan

ce

(Ω

)

Fretting cycles

23000 50000 83000

9500096000

107000

97300

ΔR<ΔRc

ΔR>ΔRc

Interrupted tests at different fretting cycles to follow the electrical degradation

Characterization of fretting scars (SEM, EDX 3D profil)

δg= 9µm Ag/Ag e= 2µm P=3N f=30Hz RH=10% T=25°C δ0= 9µm)

20 20

J. Song et al. Wear 330–331, (2015

Y.W. Park et al. Tribology International 41(7),(2008)

J. Laporte et al., Wear 330-331(2015), 170–181.

26/09/2017

11

ΔR>ΔRc=4mΩΔR<ΔRc=4mΩ

N=40000 cycles

R=0,48mΩ

Nc=87000 cycles

R=5,04mΩ

N=10000 cycles

R=0,58mΩ

N=1025 cycles

R=0,13mΩ

Inférieur

Supérieur

δ*g

δ*g

upper specimen

lower specimen

Investigation of fretting wear damages

0

1

2

3

4

5

6

7

8

9

10

0 20 000 40 000 60 000 80 000 100 000

ΔR<ΔRc

ΔR>ΔRc

Nc

20000

1000

5000

10000

40000 60000

80000

87000

R(mΩ)

fretting cycles

Electrical failure Nc: ΔR>ΔRc=4mΩ related to a

threshold chemical composition of debris layer :

when [Ag]0.2<[Ag]th≈5%at & [0]>[0]th > 45%

then ECR failure.

fretting cycles

ECR failure

0

10

20

30

40

50

60

70

80

90

100

0 20000 40000 60000 80000

concentr

atio

n a

t%

O Ag

[O]th= 45at%

100000

[Ag]th= 5at%

EDX analysis in the central zone (20% of fretting scar)

Øa

Øc Øa=0,2.Øc

21 S. Fouvry et al. Wear, 271 (9-10), 2011, 1524-1534.

J. Laporte et al., Wear 330-331 (2015), 170–181.

0

10

20

30

40

50

60

0 200000 400000 600000 800000 1000000

co

nc

en

tra

tio

n (

At.

%)

ECR endurance, Nc (cycles)

[O]%

[Ag]%

[O]th=45At.% 5At.%

[Ag]th=5At.% 3.5At.%

Øf

averaged

EDX analysis

d = 0.2 Øf

Stable if similar area is analyzed (inner 20% of the fretting scar radius observed At the Nc ECR failure)

Ag/Ag, e=2µm, P=3N, f=30Hz, T=25°C, RH=10%, δ0=±4µm to ±16.75µm

Stability of the proposal ?

22

[Ag]

[Ni]

[0]

[Cu]

EDX mapping

upper

lower

upper

lower

upper

lower

upper

lower

ΔR< ΔRc ΔR>ΔRc

26/09/2017

12

Investigation of fretting wear damages EDX Analysis at the Nc failure

Fretting scar at Nc (ECR failure)

The most stable criterion [O]th = 45 At.%

23/19

The ECR failure is reached when the fretting scar is fully covered by an oxide debris layer

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

0 0.2 0.4 0.6 0.8 1

d/Øf

[O]

[Ag]

At. %

Øf

d diameter of EDX spot

J. Laporte et al., Wear 330-331 (2015), 170–181.

Investigation of fretting wear damages EDX Analysis at the Nc failure

Chemical concentration profiles at the ECR failure (Nc)

Ag

Ni

Cu

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800

Co

ncen

trati

on

(A

t.%

)

Position in the fretting track (µm)

NiOAgCu

Fretting track

Analysis zone e=1µm

24/19

The Nc failure (ΔR>ΔRc=4mΩ) is reached when Ag is remove from the center of the fretting scar (still present in the lateral sides)

Test conditions: P=3N δ0= 9µm

RH=10%

f=30Hz

T=25°C

e=2µm

EDX scan

A. Kassmann Rudolphi et al. Wear 201, (1996)

S. Noël et al. Proc. 52nd IEEE Holm, (2006)

J. Laporte et al., Wear 330-331 (2015), 170–181.

26/09/2017

13

4. Quantification using a friction energy wear approach

25

Prediction of ECR endurance: energy approach Normal force influence on ECR endurance

12/19

Need a global wear parameter to combine δ0 and P!

Ag/Ag HR=10% e=2 µm f=30Hz T=25°C

0

2

4

6

8

10

12

14

16

18

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10

slid

ing

am

plit

ude

, δ

0(

µm

)

ECR endurance, Nc (cycles)

P=6N

P=5N

P=4N

P=3N

P=2N

P=1N

(6 )

(6 )

(6 )

0( )

N

N

N n

NcNc

(1 )

(1 )

(1 )

0( )

N

N

N n

NcNc

increasing P

An increase of P decrease Nc for a given δ0

S. Fouvry et al. 58th IEEE Holm , 2012, 191-203

J. Laporte et al., Wear 330-331 (2015), 170–181.

26/09/2017

14

Friction Energy Wear Approach

(Global Wear Volume)

Friction Work

S

Surface transformation & degradations S

wear volume

EdS

EdS

Wear Volume

Q (N)

* (m)

frettingcycles

Q (N)

* (m)

frettingcycles

Q (N)

* (m)

frettingcycles

Q (N)

* (m)

frettingcycles

Q (N)

* (m)

frettingcycles

Q (N)

* (m)

frettingcycles

27

S. Fouvry et al., Wear, 200 (1996), p. 186-205

maximum

wear depth (h)

accumulated

friction energy density profile

modification of the contact

geometry

modification of

the contact pressure

modification of the

energy density

distribution

coupled

problem

max

Wear

profile

FEMRF1

RF2

wear box

Nc

electrical contact resistance

Wear

Volume Substrate

interactions

need to predict wear depth !

Friction Energy Local Approach

28 S. Fouvry et al. Wear 255, 2003, 287-298

C. Mary et al. Wear263 (1-6), 2007,444-450

26/09/2017

15

Prediction of ECR endurance: energy approach Application of friction energy approach

Nc prediction requires a local wear approach

z (µm)

)(xmax

maxh

Wear Profile

energy density

with wear ϕ(x) converge to a flat profile

Very nice prediction

(low dispersion)

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

2000000

0 1000 2000 3000

φf = Ed/Af (J/m²/cycle)

P=6NP=5NP=4NP=3NP=2NP=1N

𝑁𝑐 = 𝑁𝑐0.𝜑𝑓𝛽

Nc0=6.1012cycles

and β=-2.58

Nc (cycles)

Ag/Ag HR=10% e=2 µm f=30Hz T=25°C

)( f

NcNc

Ncϕ= 6 1012 cycles β=2.58

Af=A final

fretting loop

contact area

ff

Ed

A

29 C. Mary et al. Wear 263 J. Laporte et al., Wear 330-331 (2015), 170–181.

Prediction of ECR endurance: energy approach Simplified approximation

Possibility to approximate Af using a single power law function of normal force: with A0=72,600 µm² and m=0.256

Previous analysis requires the measurement of Af (long & fastidious)

0

20000

40000

60000

80000

100000

120000

140000

160000

0 2 4 6 8

P(N)

A (µm²)

𝐴𝑓 = 𝐴0 .𝑃𝑚

The analysis requires the computation of Ed! (integrale of the frettting loop) Considering a quadratic shape:

04Ed P

µ.P

02

30 Ed

26/09/2017

16

Prediction of ECR endurance: energy approach Simplified approximation

1000

10000

100000

1000000

10000000

1000 10000 100000 1000000 10000000

Nc

exp

(cycle

s)

Ncth (cycles)

e=2µm, 2µm<δg< 16µm

P=6NP=5NP=4NP=3NP=2NP=1N

Very good correlation between experimental lifetime and

theoretical prediction

𝐴𝑓 = 𝐴0 .𝑃𝑚

Ed

ANc

NcNc

f

f )( )1(

0

0 1

4 mPµ

ANcNc

31 J. Laporte et al., Wear 330-331 (2015), 170–181

PµEd ...4 0

Prediction of ECR endurance: energy approach Influence of the coating thickness

32

A thicker coating induce a significant lateral contact extension!

VAg α eγ with γ>1

e

Parabolic evolution:

𝑁𝑐

𝑁𝑐𝑟𝑒𝑓=

𝑒

𝑒𝑟𝑒𝑓

𝑝

p=2.85 eref=2µm Ncref=Nc(2µm)

0

200000

400000

600000

800000

1000000

1200000

1400000

0 1 2 3 4 5 6

Coating thickness (e)

Nc (cyclesAg/Ag P=3N δ0= 9µm HR=10% f=30Hz T=25°C

J. Laporte et al., Wear 330-331 (2015), 170–181

26/09/2017

17

Prediction of ECR endurance: energy approach Global formulation

Very good correlation confirming the proposal !

Ncth=f(P, δ0, µ)

𝑁𝑐

𝑁𝑐𝑟𝑒𝑓=

𝑒

𝑒𝑟𝑒𝑓

𝑝

Ncth=g(P, δ0, µ, e)

Normal force

Sliding amplitude

Friction coefficient

Thickness

1000

10000

100000

1000000

10000000

1000 10000 100000 1000000 10000000

Nc

(experi

me

nta

l) (c

ycle

s)

Nc(predicted) (cycles)

e=2µme=3µme=4µme=4.8µm

Eq. (21)P=3N,

2µm <δ0< 16µm

Eq. (15), e=2µm, 2µm <δ0< 16µm

P=6NP=5NP=4N

P=3NP=2NP=1N

p

ref

m e

e

Pµ

ANcNc

)1(

0

0 1

4

33

J. Laporte et al., Wear 330-331 (2015), 170–181

5. Complex Fretting-Reciprocating slidings

34

26/09/2017

18

before insertion after insertion

repetitive insertions

Surface degradations

Influence of repetitive clipping & uncliping slidings

pin

clip flexible

?

0.0001

0.001

0.01

0.1

1

0 100000 200000

R [Ω

]

Nombre de cycles N

electrical failure

Nc Nc

pin

clip flexible

35

tangentiel forcesensor

flexiblestrips

samples

upper sampleholderflexible

strips weight

electromagneticlinear motor

(reciprocating)

electromagneticshaker

(fretting)

laser sensor

9 µm

ΔR >ΔRc

δ0= 9 µm (30 Hz)

Test stopped when

D

D= 250µm to 1 500µm vGC,ref= 8,3µm.s-1 to 124,5µm.s-1

fretting Nf 5 000 à 60 000cycles

Ag/Ag HR=10% e=2 µm f=30Hz T=25°C

Experimental strategy

Real clip assembly

fretting track

reciprocating track

J. Laporte et al., Wear 376-377 (2017) 656–669.

26/09/2017

19

N=60 000 cycles

0 = 9µm

Large sliding

D=1mm

R = 2.14mΩ A

δ*g

[Ag]≈17at%

δ*g

Fretting zone

Reciprocating zone [Ag]≈31at%

[Ag]≈87at%

refilling process : Ag is transferred from the external reciprocating track scar to the fretting scar ! => The application of reciprocating increase the ECR endurance !

Ag/Ag RH=10% e=2 µm f=30Hz T=25°C

Effect of reciprocating sliding regarding ECR fretting response

37

R = 2.14mΩ

B

plain frettingfretting-reciprocating

δ*g

δ0

0

2

4

6

8

10

12

0 50 000 100 000 150 000 200 000

fretting cycles (N)

ΔR=4mΩ

plain fretting(D=0µm)

Nc= 100,000 cycles

reciprocating sliding

ele

ctr

ical

co

nta

ct

res

ista

nc

e,

R (

mΩ

) Nf = 10000 cycles

Fretting

N cycles

D

9 µm

reciprocating stroke (D= 1 mm)

fretting

sequence

fretting & reciprocating

Nc= 201,700 cycles

300 µm

[Ag]=2.2at%

[O]=12.8at%

[Ag]=3.4at%

[O]=43.6at%

[Ag]=5.17at%

[O]=48.13at%

All Ag present in reciprocating track is transferred

max (0)

(0)

,1 /f f tr

Nc NcNc Nc

N N

0

5

10

15

20

25

0 2 4 6 8 10

x 1

00

00

Nf,tr

plain fretting

(NR=0), Nc(0)

Ncmax

x104

x104

NR=0

NR=1

NR=2

NR=4

NR=10

NR=20

NR=40

fre

ttin

ge

nd

ura

nce

, N

c(c

ycle

s)

(Eq.23)

fretting cycles between eachreciprocating sliding, Nf (cycles)

Nf too long => no transfer

Influence of fretting block (periodicity of large sliding) ?

38 J. Laporte et al., Wear 376-377, (2017) 656–669.

Nf

Nc : total number of fretting cycles before ERC failure

26/09/2017

20

39

Influence of reciprocating stroke ?

0

5

10

15

20

25

30

35

40

0 250 500 750 1,000 1,250 1,500 1,750

x 10

000

reciprocating stroke, D (µm)

Dc

Dth

plain fretting,

NcPF

x104

fre

ttin

g e

nd

ura

nce

, Nc

(cyc

les)

Non monotonic evolution

Nc prediction (global formulation)

40

Vc : total Ag volume involved in fretting wear process

0

1

2

3

4

5

6

7

8

9

10

0 500 1,000 1,500 2,000

reciprocating stroke, D (µm)Dth

Steady-state

PFfV ,

ccf

NVV

we

ar

rate

,

(µ

m3/

cycl

e)

Nf=Nf,ref =10,000cycles250µm D 1,500µmplain fretting

PFfreff VhV ,,

determined for Dref=1mm

with h=1.66

v

tr

PFf

D

D

hhVV

1

1,

VcV

Nc

(µm3/cy.)

[ ]2

f

Ag fVc k V k e D

wear rate

1

,

*

,1

1

124

v

tr

w

trf

f

f

gPFf

fcc

D

D

hh

N

N

D

PK

ek

V

VN

0

5

10

15

20

25

30

35

40

0 10 20 30 40

Nc e

xp

(cyc

les)

Ncpred (cycles)

x104

x104

D=Dref=1mm5,000cycles Nf 60,000cyclesNf=Nf,ref=10,000cycles250µm D 1,500µmplain fretting

V

VcNc

total Ag volume involved in fretting wear process @ Nc

V : wear rate per fretting cycle

J. Laporte et al., Wear 376-377, (2017) 656–669.

k = 0.94 (proportion of volumetric Ag volume involved)

26/09/2017

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41

6. Simplified strategy to compare coatings : ECR versus Coatings properties ?

Ncref : Reference ECR endurance defined for a reference sliding amplitude δ0=± 9µm

ECR endurance, Nc

δ*0 =±9µm

310 410 510 610 710 810 910 10100

5

10

15

20

25

30

1110

0 (±µm)

“power law function”

δ0=9µm

Ncref

the larger Ncref and _ref , the better the electrical performance !

cold welding index _ref=1/µmax (δ0=9µm)

0.0

0.5

1.0

1.5

2.0

2.5

0 5000 10000 15000

µmax

µ=Q*/P

fretting cycle

Definition of two driving parameters to describe GS ECR endurance & Cold welding

26/09/2017

22

Ni

AgSn

CuZn37 (substrat)

e=2µm

2 µm

Ni

AgCrN

CuZn37 (substrat)

e=2µm

2 µm

Ni

AgSnIn

CuZn37 (substrat)

e=2µm

2 µm

Ni

AgaC

CuZn37 (substrate

e=2µm

2 µm

New coating via Ag PVD

Possibility to explore new hardnesses and new conductivities !

Comparison of coatings

0

5

10

15

20

25

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1 x104

AuNi AgaC AgCrN AgSn AgSnIn Ag

ref=1/µmax Ncref (cycles)

considering ref & Ncref

the best compromise is obtained with AgSnIn (conductive ITO oxydes)

Conditions de test: P=3N δ0 = 9µm RH=10% f=30Hz T=25°C

e=2µm et eAuNi=1,3µm

44

Comparison of coatings

cold welding index

GS fretting endurance

index

Laporte et al. , IEEE 61st Holm Conference, 2015, 287-297

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Correlation of Nc_ref versus Hardness & conductivity

0

5

10

15

20

25

0 100 200 300 400 500

AgSnIn

conductive oxydes (ITO)

Hardness, H (hv)

Nc (x 10000)

Ag

AgaC

AuNi AgCrN

AgSn

High scattering : Hardness is not a relevent parameter

0

5

10

15

20

25

0.00 0.20 0.40 0.60 0.80

electrical conductivity , σ (µS.cm-1)

Nc (x 10000)

AgCrN

AgSn AuNi

AgSnIn

AgaC

conductive oxydes

Ag

Removing (AgSnIn) => Linear increase

)(NcNc VVCNc

CVNc c ≈ Cst (base Argent)

CVNc

NcV

45 Ncref is proportional to the coating conductivity

46

Tribological interpretation :

0

5

10

15

20

25

30

35

40

0 0.2 0.4 0.6 0.8

σ (µS.cm-1)

x104

AgSnIn

AgSn

AgCrN

Ag

AgaC

AuNi

0,NcV

NcVC

VNc (µm3)

the wear volume at the ECR failure is proportional to the coating conductivity

VNc ( x 104 µm3)

The higher the coating electrical conductivity , the larger the wear volume required to reach ECR failure → Nc is proportional to the coating conductivity

0

5

10

15

20

25

30

35

40

45

50

0 50000 100000 150000 200000 250000

KNc=1,82µm3/cycle

AgSnIn

AgSn AgCrN

Ag

AgaC

AuNi

Nc (cycles)

wear volume measured at Nc is proportional to the Nc

VNc ( x 104 µm3)

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47

Conclusions

- The partial slip/ gross slip displacement transition controls the transition from infinite to finite ECR endurance (Nc : N_fretting when Δ R>4 mΩ) - Nc is controlled by surface wear processes: ECR failure is reached when [O] > 45 at% (noble metal eliminated and replace by a oxide layer) - Nc can be expressed as a power law function of friction energy density ϕ (Wear depth is controlled by ϕ) - Nc can be expressed as a power low function of sliding amplitude (deduced from the general friction energy density formulation)

- Application of large sliding induced a noble metal “refilling” process of fretting scar (Increase of Nc) - The global response of a coating can described by two variables - Ncref (GS endurance index) & χ ref (cold welding index)

- Nc_ref is controlled by the electrical conductivity of the coating

t

[O]

)( f

NcNc

n

NcNc

)( 0

Thank you for your attention !