Friction Behavior of DLC filmFriction Behavior of DLC filmwith Environmental Changeswith Environmental Changes

Copyright, 1997 © Dale Carnegie & Associates, Inc.

S. J. Park*, K.-R. Lee*, D.-H. Ko+, K. Y. Eun** Korea Institute of Science & Tech.

Future Technol. Research Division

+ Yonsei University Dept. of Ceramic Eng.

Frictional Properties of Hard Coating Films

DLC

WC

TiN

CrN

TiCN

Wear Rate Friction Coefficient

2.0 1.6 1.2 0.8 0.4 0.2 0.4 0.6 0.8 1.0Relative value

Various Applications of DLCVarious Applications of DLC

Disadvantages of Pure DLC Film

• High internal compressive stresses(~ 9 GPa)

result in poor adhesion.

• The friction behavior depends on

environment

(especially dependent on humidity)

Previous Works

• K. Y. Eun et al, Surf. Coat. Technol. 86-87 (1996) 569

– High and unstable friction coefficient of DLC films in vacuum

– Formation of roll-shaped polymeric debris in vacuum

• S. H. Yang et al, Wear 252 (2001) 70– Increase of friction coefficient with the increase of humidity

– Agglomeration of small debris

Purposes of This Work

• To test the friction behavior of DLC film in various environment environment, especially such as humidity

• To find the reason of dependence of humidity in DLC films in the point of tribochemical reaction

Deposition Condition

• RF PACVD(13.56 MHz)

• Precursor Gas : C6H6, C6H6 + SiH4,

• Deposition Pressure : 1.33 Pa

• Bias Voltage : - 400 Vb

Substrate : P-type (100) Si-wafer

• Film thickness : 1 ㎛

• Si concentration : 2 at.%

Friction Test Condition

Motor

Constant

Temperature and

Humidifier

Rotary Pump

Ball : AISI 52100 Steel Ball, Al2O3

Normal Load : 4 N

Speed : 220 rpm

Temperature : Room temperature

Environment Gas

Atmosphere

(relative humidity : 0 – 90 %)

Ultra high purity oxygen

Normal

Load

Film

Friction Coefficient of DLC FilmFriction Coefficient of DLC Film

a-C:H Si-C:H

Images of Ball Scar (a-C:H)

• RH : 90 %• RH : 0 % • RH : 50 %

100 ㎛ 100 ㎛ 100 ㎛

Wear Rate of Track and Ball

Track

Ball

• a-C:H • Si-C:H

Relationship between Friction Coefficient and Ball Wear Rate

Friction Behavior with Environment

• RH : 50 %

Ball

a-C:H

• RH : 0 % • RH : 90 %

Ball

a-C:H

C-O-Fe C-O

Ball

a-C:H Fe-O

AES Spectra of Track Debris (a-C:H)

a-C:H

a-C:H

a-C:H

FeFe-O

FeFe-O

FeFe-O

Friction Coefficient in Oxygen Environment

Wear Rate of Track and Ball (O2 Env.)

Track

Ball

• a-C:H • Si-C:H

AES Sepectra of Track (O2 Env.)

a-C:H

a-C:H

Si-C:H

Fe

Al2O3

Fe

Fe-O

Fe-O

a-C:H

Conclusions

The increase of friction coefficient with the increase of humidity depends on the oxidation of steel ball

Iron rich debris by oxidation of steel ball plays key role of the

increase of friction coefficient

Friction coefficient of Si-C:H film is low and stable in oxygen environment

Silicon rich debris by severe wear of film decreases the friction

coefficient

G-peak Position of the Film and Scar(a-C:H)

Photograph of Wear Track (a-C:H)

• RH : 90 %• RH : 0 % • RH : 50 %

Photograph of Wear Track (Si-DLC, 2 at.%)

250 ㎛

250 ㎛

• RH : 90 %• RH : 0 % • RH : 50 %

250 ㎛

Photograph of Track and Ball (O2 Env.)

Track

Si-C:H With Steel Ball

Ball

a-C:H With Steel Ball

a-C:H With Al2O3 ball

100 ㎛

100 ㎛

100 ㎛

250 ㎛250 ㎛250 ㎛