In Situ Tribometry Studies of Nanocomposite Coatings

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In Situ Tribometry Studies of Nanocomposite
Coatings

• Richard R. Chromik1,2, Colin C. Baker2,3,
• Andrey A. Voevodin3 Kathryn J. Wahl1
• 1U.S. Naval Research Laboratory, Code 6176,
  Tribology Section
• 2North Carolina State University, Department of
  Physics
• 3U.S. Air Force Research Laboratory, Materials
  and Manufacturing Directorate

Extreme Friction MURI Review Meeting February 19,
2006, Irvine, CA Dr. Jacqueline Krim, PI, NCSU
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Why Nanocomposite Coatings?
Dry, Vacuum Environment MoS2
Ambient, Humid Environment DLC
Nanoscale Lubricant Reservoirs
Air or space 500-800 C Au
A.A. Voevodin, T.A. Fitz, J.J. Hu, and J.S.
Zabinski, J. Vac. Sci. Tech. A 20, 1434 (2002).
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Nanocomposite CoatingsYSZ/Au/DLC/MoS2

• Robust coatings in dry and humid environments
• All coatings 14 18 MoS2
• Coatings grouped according to Au content

JVST A.A. Voevodin, T.A. Fitz, J.J. Hu, and J.S.
Zabinski, J. Vac. Sci.Techn. A 20, 1434 (2002).
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Mechanical PropertiesNanoindentation
Nanoindentation testing in low-cycle tracks
Post-imaging allows for identification of suspect
indents near porosity or track damage
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Mechanical Properties Nanoindentation
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Motivation

• Expand range of coating stoichiometry
• Previous work 50 YSZ, 10 Au, 20 C and 20
  MoS2

YSZ 33 59 Au 10 34 C 11 36
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Motivation

• Expand range of coating stoichiometry
• Previous work 50 YSZ, 10 Au, 20 C and 20
  MoS2
• Perform in situ tribometry
• Velocity accommodation modes (VAM)
• Wear mechanisms (plowing, debris transfer, etc.)

YSZ 33 59 Au 10 34 C 11 36
Interfacial Sliding
Real-time observation on contact
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Motivation

• Expand range of coating stoichiometry
• Previous work 50 YSZ, 10 Au, 20 C and 20
  MoS2
• Perform in situ tribometry
• Velocity accommodation modes (VAM)
• Wear mechanisms (plowing, debris transfer, etc.)

YSZ 33 59 Au 10 34 C 11 36
Interfacial Sliding
Interfilm Shearing
Solid Lubricant Coating
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In situ Tribometer
In situ image of the contact
Load 6.4 N (0.9 GPa) Speed 1 mm/s Cycle up to
1500
In ex situ Raman spectroscopy
Environments Dry N2 (3 5 RH) Humid air (35
45 RH)
Optical microscope
Nanocomposite coating
Six YSZ/Au/DLC/MoS2coatings
T.W. Scharf and I.L. Singer, Tribol. Letters 14,
3 (2002). I.L. Singer, S.D. Dvorak, K.J. Wahl and
T.W. Scharf, J. Vac. Sci. Technol. A 21, S232
(2003).
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Sliding in Humid Air
Low Au
High Au

• Smooth run-in for both low and high Au coatings.
• Average steady state friction between 0.06 and
  0.08
• L1, L2 and H1 show friction instability

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Sliding in Dry N2
Low Au
High Au

• Low Au coatings showed extended run-in
  compared to high Au
• Average steady state friction was between 0.04
  and 0.05
• L1, L2 and H1 exhibited friction spiking!

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Tribology Results
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In Situ ObservationsVelocity Accommodation
High Au
Smooth Run-In Transfer film formation
Coating H3 in Air, 40 RH
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Dry Sliding, Run-In
High Au
Low Au

• Low Au coatings showed extended run-in when
  compared to High Au coatings.

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In Situ ObservationsExtended Run-In
Coating L3 in N2 4 RH

• Extended Run-in
• High friction, plowing

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In Situ ObservationsExtended Run-In
Coating L3 in 4 RH

• Extended Run-in
• High friction, plowing
• Friction drop
• More uniform transfer film
• Plowing disappears

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In Situ ObservationsFriction Spiking
Coating H1 In 4 RH
FRICTION SPIKING observed for coatings H1, L1
and L2
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Summary of In Situ Observations

• All coatings exhibited primarily interfacial
  sliding (humid and dry)
• All coatings had some component of interfilm
  shearing for humid conditions

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Conclusions

• Steady state friction was found to be somewhat
  independent of coating composition.
• Departures from steady state friction depend on
  coating composition and/or mechanical properties
• In dry conditions, low Au coatings exhibited
  extended run-in due to plowing
• In both dry and humid conditions, coatings with
  high YSZ content showed friction spiking (plowing
  and transfer film extrusion)

0.06 0.08 for Humid 0.04 0.05 for Dry
Low Au Harder and Higher Modulus
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Publications and Short Term GoalsNanocomposite
Coatings

• Submitted, Accepted or Published
• R.R. Chromik, C.C. Baker, A.A. Voevodin and K.J.
  Wahl, In situ optical tribometry of
  nanocomposite coatings., submitted for MRS
  Proceedings, Fall Meeting 2005.
• In Preparation
• C.C. Baker, R.R. Chromik, K.J. Wahl and A.A.
  Voevodin, Tribological behavior of
  YSZ/Au/DLC/MoS2 nanocomposite coatings of varying
  compositions.
• R.R. Chromik, C.C. Baker, A.A. Voevodin and K.J.
  Wahl, In situ tribology investigation of
  YSZ/Au/DLC/MoS2 nanocomposite coatings.
• On the Horizon
• Do these different wear mechanisms result in
  different wear rates? (Another paper on wear
  rates of these coatings)
• Alumina coatings new coating system, conduct
  similar studies at NRL on selected coatings.

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Ex situ Raman Analysis
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Three Component CoatingsWhat is Lubricating?

• Removal of C does not change friction
  properties of the nanocomposite
• Removal of MoS2 results in high friction and
  early failure

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YSZ/Au/MoS2/DLC preparation using
MSPLD Magnetron Sputtering - Pulsed Laser
Deposition
substrate holder -150 V bias
Ar flow
150 C 300 C
pulsed laser beam 248 nm, 600 mJ, 16 ns, 40-60
Hz
sectioned target
Au magnetron Vary power
YSZ
MoS2
graphite
Au
YSZ
A.A. Voevodin, T.A. Fitz, J.J. Hu, and J.S.
Zabinski, J. Vac. Sci. Tech. A 20, 1434 (2002).
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Design of YSZ/Au/MoS2/DLC Nanocomposite Coatings
Tough-hard-low m
YSZ
50 um
200g load
YSZ nanocomposite
1000g load
50 um
A.A. Voevodin, T.A. Fitz, J.J. Hu, and J.S.
Zabinski, J. Vac. Sci.Techn.A 20, 1434 (2002).
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Low Humidity Friction Behavior
Spatially Resolved Friction vs. Cycle
6 mm
Friction vs. Track Position
Average Friction vs. Sliding Cycle
6 mm

• Friction spikes occur along entire track, not
  locally
• Contact heals (back to lower friction)

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High Humidity Friction Behavior
Spatially Resolved m vs. Cycle
6 mm
Average m vs. Cycle
m vs. Track Position
6 mm

• Higher friction spots are local, rather than
  along entire track