상대재에 따른 상대재에 따른 DLC DLC 필름의 필름의 마찰마모특성의 습도 의존성마찰마모특성의 습도 의존성

2005 2005 춘계 학술대회춘계 학술대회

Se Jun Park, Kwang-Ryeol Lee, Seung-Cheol Lee,

Future Technology Research Division,

Korea Institute of Science and Technology

Tribological 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

Dependence of Tribological Behavior of DLC Films on Humidity

R. Gilmore et al Surf. Coat. Technol. 133-134, (2000), 437

Previous Works about the Environmental Dependence

Y. Kokaku et al. J. Vac. Sci. Technol. A 7 (1989) 2311

High friction coefficient in humid environment An unstable oxide layer on DLC film surface

involved in humid environment

B. Marchon et al, IEEE Trans. Magn. 26 (1990) 2670

Surface smoothness of DLC film by chemisorbed oxygen

The increase of real contact area

C. Donnet et al., Tribo. Letters, 4 (1998) 259

Prevention of the growth of the carbonaceous transfer film by the water vapor

DLC

Counterface

Reaction with H2O

Transfer layer

FN

FF

Tribology Process of DLC Film in Humid Air

DLC

Reaction with H2O

Reaction with H2O

FN

FF

Tribology Process of DLC Film in Humid Air

Tribo-chemical reaction

Transfer layer Material transfer

Counterface

Friction Coefficient of DLC FilmFriction Coefficient of DLC Filmand Counterfaceand Counterface

RH : 0 %

DLC against steel ball

RH : 50 %

RH : 90 %

2 ㎛

2 ㎛

2 ㎛

+

• S. J. Park et al, Diam.Rel.Mater., 12 (2003) 1517• S. J. Park et al, Tribol. Intl., 37 (2004) 913

Friction Behavior of DLC Using Steel Friction Behavior of DLC Using Steel Ball with the Change of HumidityBall with the Change of Humidity

• RH : 0 %Low oxidational wear of ball

• RH : 90 %High oxidational wear of ball

Frictioncoefficient

RelativeHumidity

• Formation of Fe-rich debris (Degradation of lubricant properties of DLC film)• Increase of the debris size

Steel

DLC

C-O-Fe

Fe-oxide

C-OSteel

DLC

MotivationsMotivations

DLC

If the formation of Fe-rich debris is suppressed, what will happen?

Steel

DLC

Purposes of the Present WorkPurposes of the Present Work

To characterize the tribological behavior of DLC film with the humidity change in various tribo-system. DLC against steel ball DLC against DLC coated ball

To find the reason for the humidity dependence of frictional behavior of DLC film in the view point of tribo-chemical reaction.

Deposition ConditionDeposition Condition

•RF PACVD(13.56 MHz)

•Precursor Gas : C6H6

•Deposition Pressure : 1.33 Pa

•Bias Voltage : - 400 Vb

•Substrate : P-type (100) Si-wafer

•Film Thickness : 1 ㎛

•Residual Stress : 0.9 ± 0.02 GPa

•Hardness : 11 ± 0.5 GPa

Tribo-test ConditionTribo-test Condition

• Ball-on-disc type tribometer isolated by chamber

• Counterface : AISI 52100 steel ball

DLC coated steel ball

• Normal Load : 4 N

• Rotation Speed : 20 cm/s

• Temperature : Room temperature

• Test Environment:

Ambient atmosphere

(Relative humidity : 0 – 90 %)

Film

Hygrometer

NormalLoad

Loadcell

Humidity controller

Rotary Pump

Friction Coefficient of DLC film Friction Coefficient of DLC film with Humidity Changewith Humidity Change

Chemical Composition of Debris Chemical Composition of Debris with Humidity Changewith Humidity ChangeDLC against DLC coated ball

Friction Coefficient and Friction Coefficient and Chemical Composition of the Chemical Composition of the DebrisDebris

Morphology of Debris on Track Morphology of Debris on Track with Humidity Changewith Humidity Change

RH : 0 % RH : 50 % RH : 90 %

2 ㎛ 2 ㎛ 2 ㎛

DLC against DLC coated ball

Friction Coefficient and Friction Coefficient and Chemical Composition of the Chemical Composition of the DebrisDebris

Raman Spectra of Transfer Raman Spectra of Transfer LayerLayer

DLC Coated Ball Steel Ball

Friction Coefficient Vs. Relative Humidity

Structure of Transfer Layer and Structure of Transfer Layer and Friction coefficient of Si-DLC filmFriction coefficient of Si-DLC film

Raman spectra of transfer layer of Si-DLC

• S. J. Park et al, Tribol. Intl., 37 (2004) 913

Raman spectra of transfer layer of DLC

Schematic Diagram of Friction Schematic Diagram of Friction Behavior in Humid AirBehavior in Humid Air

Formation of large size of debris

Formation of Fe-rich debris Formation of graphitic transfer layer Incorporation of Fe itself

Absence of Fe in debris Formation of diamond-like structure

of transfer layer

DLC

DLC

Steel

Steel

DLC

DLC Coated Ball

Steel Ball

Which is the major Contribution Which is the major Contribution of Fe incorporation?of Fe incorporation?

Fe-rich debris Fe-rich debris

RH : 90 % RH : 0 %

Graphitic transfer layer that is sensitive to humidity Incorporated Fe in debris itself

Abrupt change of humidity

Steel Steel

Abrupt change

of humidity

during tribo-test

Incorporation of Fe in debris itself

The formation of the graphitic layer sensitive to humidity

Gradual change of friction coefficient

Abrupt change of friction coefficient

Friction Coefficient with Friction Coefficient with Humidity Change during Tribo-Humidity Change during Tribo-testtest

The effect of Fe in debris on the friction behavior The formation of the graphitic transfer layer highly

sensitive to humidity`

The immediate drop of the friction coefficient

RH : 90 % RH : 0 %

ConclusionsConclusions

Using steel balls, the tribological behavior of DLC film was highly affected by humidity.

• Incorporated Fe in debris by wear of the steel ball enhanced the formation of highly graphitic layer.

The graphitic transfer layer was strongly sensitive to the humidity.

• When a graphitic transfer layer was formed, the friction coefficient of DLC film increased in humid environment.

Counterface materials should be chosen carefully in order to control the tribological behavior of DLC films.