Humidity Dependence of Tribological Behavior of DLC Film Se Jun Park *#, Kwang-Ryeol Lee *,...
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Transcript of Humidity Dependence of Tribological Behavior of DLC Film Se Jun Park *#, Kwang-Ryeol Lee *,...
Humidity Dependence of Humidity Dependence of Tribological Behavior of DLC Tribological Behavior of DLC FilmFilm
Se Jun Park*#, Kwang-Ryeol Lee*, Seung-Cheol Lee* and Dae-Hong Ko#
*Korea Institute Science and Technology#Yonsei University
Tribological Properties Tribological Properties of Hard Coating Materialsof Hard Coating Materials
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 Dependence of Tribological Behavior of DLC Films on Humidityof DLC Films on Humidity
It is important to understand the tribological behavior of DLC films in humid environment
R. Gilmore et al Surf. Coat. Technol. 133-134, (2000), 437
Previous WorksPrevious Works
Surface smoothness of DLC film by chemisorbed oxygen
The increase of real contact area
The prevention of the growth of the carbonaceous transfer film by the water vapor
• C. Donnet et al., Tribo. Letters, 4 (1998) 259
• B. Marchon et al, IEEE Trans. Magn. 26 (1990) 2670
Tribology Process of DLC FilmTribology Process of DLC Film
DLC
Counterface
Wear
Reaction with environment
Reactionwith environment
Materialtransfer Transfer layer
FF
FN
Friction Coefficient
F
N
FF
=
Tribo-chemical reaction
Purposes of Present WorkPurposes of 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 view 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 : 10.5 ± 0.5 GPa
Tribo-test ConditionTribo-test Condition
• Ball-on-disc type tribometer isolated by chamber
• Ball : AISI 52100 steel ball
DLC coated steel ball
• Normal Load : 4 N
• Rotation Speed : 220 rpm
• Temperature : Room temperature
• Environmental Gas :
Ambient atmosphere
(Relative humidity : 0 – 90 %)
Film
Hygrometer
NormalLoad
Loadcell
Humidity controller
Rotary Pump
Friction Coefficient with Humidity Friction Coefficient with Humidity Change Using Steel ballChange Using Steel ball
Images of Transfer Layer on ScarImages of Transfer Layer on Scar
RH 0 %
100 ㎛
RH 50 %
100 ㎛
RH 90 %
100 ㎛
Morphology of Debris on TrackMorphology of Debris on Track
2 ㎛ 2 ㎛ 2 ㎛
RH 0 % RH 50 % RH 90 %
Relativehumidity
Size ofdebris
Frictioncoefficient
Chemical Composition of DebrisChemical Composition of Debris
Chemical Composition of DebrisChemical Composition of Debris
• Kim et al, Surf. Coat. Techno. 112 (1999) 204
Chemical Composition of DebrisChemical Composition of Debris
Wear of steel ballFriction
coefficientFe concentration
in debris
Friction Behavior with HumidityFriction Behavior with Humidity
RH : 50 % RH : 0 % RH : 90 %
Steel
DLC
Steel
DLC
C-O-Fe C-O
Steel
DLC
Fe-Olow oxidation of ball high oxidation of ball
Frictioncoefficient
RelativeHumidity
Formation of Fe-rich debrisIncrease of the debris size
MotivationsMotivations
Steel
DLC
DLC
If the formation of Fe-rich debris was suppressed ?
Friction Coefficient with Humidity Friction Coefficient with Humidity ChangeChange
Chemical Composition of DebrisChemical Composition of Debris
Micrographs of Debris on Track Micrographs of Debris on Track with Humidity Changewith Humidity Change
0 % 50 % 90 %
3 ㎛ 3 ㎛ 3 ㎛
Friction Coefficient with Humidity Friction Coefficient with Humidity ChangeChange
Raman Spectra of Transfer LayerRaman Spectra of Transfer Layer
Steel ballDLC coated ball
Schematic Diagram of Friction Schematic Diagram of Friction Behavior in high humidityBehavior in high humidity
Increase of debris size
Formation of Fe-rich Debris Formation of graphitic layer highly
sensitive to humidity Degradation of lubricant properties of
DLC film
C-O-Fe
Formation of C-O Debris The diamond-like bonding
structure of the transfer layer
Steel
DLC
Steel
DLC
DLC
The Role of Fe in DebrisThe Role of Fe in Debris
Steel
Fe-rich debris
Steel
Fe-rich debris
RH : 90 % RH : 0 %
Formation of graphitic layer highly sensitive to humidity Degradation of lubricant properties of DLC film
Abrupt change of humidity
If the Fe in debris degraded the lubricant properties of DLC film
The friction coefficient slowly dropped though the humidity abruptly drop
Friction Coefficient with HumidityFriction Coefficient with Humidity
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 friction coefficient
RH : 90 % RH : 0 %
ConclusionsConclusions
Humidity dependence of the friction behavior of DLC film is not an inherent property of the DLC film
The graphitic layer itself was very sensitive to humidity in case of using steel ball Fe element in debris enhanced the graphitization of the transfer
layer
Tribological behavior of DLC film was highly affected by the reaction between the counterface and humidity Especially using steel ball, Fe-rich debris formed by the reaction
of steel ball and humidity affected the bond structure of the transfer layer