Synthesis of Chameleon Nanocomposite Coatings for Extreme Environment Tribological Applications

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Synthesis of Chameleon Nanocomposite Coatings
for Extreme Environment Tribological Applications

• 1,2C.C. Baker and 1A.A. Voevodin

1Materials and Manufacturing Directorate, Air
Force Research Laboratory, AFRL/MLBT, Wright
Patterson Air Force Base, OH 2 Department of
Physics, North Carolina State University,
Raleigh, NC
Extreme Friction MURI Review Meeting Feb 2006.
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Introduction

• Task The synthesis of Chameleon coatings as part
  of the AFOSR Extreme Friction MURI
  collaboration including AFRL/MLBT, NC State
  University, Naval Research Laboratory.
• Synthesis and characterization is performed at
  AFRL/MLBT, while an investigation of coating
  adaptation mechanisms is in progress at NRL by
  Rich Chromik and Kathy Wahl.
• In this talk I will examine results for
  YSZ/Au/DLC/MoS2 and Al2O3/Au/DLC/MoS2.

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Chameleon Coating Surface Adaptation
Dry, Vacuum Environment MoS2
Ambient, Humid Environment DLC
tribo skin chameleon adaptation
Air or space 500-800 C Au
High temperature adaptation!
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Design of Chameleon Nanocomposite Coatings
Preparation Structure Friction Adaptive mechanisms
A.A. Voevodin, T.A. Fitz, J.J. Hu, and J.S.
Zabinski, J. Vac. Sci.Techn.A 20 (2002) 1434
- amorphous to hexagonal MoS2 in vacuum (or dry
N2) at low temperature - sp3 (DLC) to sp2
(graphite-like) carbon in humid air at low
temperature - amorphous/poor crystalline Au to
Au grains on the surface at high temperature
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Experimental Procedure

• YSZ/Au/DLC/MoS2 Synthesis
• Filtered Vacuum Arc for Ti transition layer.
• PLD, 40Hz, 800mj. Sectioned targets.
• Magnetron Sputter Deposition Au Target.

• Coating Composition and Structure
• XPS, XRD, TEM, SEM, Raman.

• Coating Hardness and Wear Resistance
• Nanoindentation, scratch testing.

• Tribological testing
• Ball on disc-tribometer, variable environment
• Nitrogen lt1 RH, Air 40 RH, Air 500C.
• M50 Steel or Si3N4 ball sliding speeds
• 200mm/sec.

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Deposition Chamber
Substrate carousel 150C, 300C -150 V bias
Ar flow
pulsed laser, 248 nm, 800 mJ, 16 ns, 40 Hz
focusing lens
Au
Filtered vacuum arc
Ablation Target
A gradient interface layer is deposited between
substrate and coating.
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Coating Composition Results XPS
With XPS Identify components, Bonding,
Concentrations.
(YSZ)0.42Au0.31(MoS2)0.16C0.11
Mo 3d peaks Indicates MoS2.
Zr 3d peaks Shifted slightly from ZrO2
C 1s peak Indicates carbide.
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Summary of Compositions
Compositions determined with XPS
Au/YSZ ratio was varied to explore a balance
between Au supply for lubrication and YSZ
fraction for hardness and abrasion resistance.
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Coating Structure XRD
Increase in Deposition Temperature and Decrease
in Au Sputter Power Gives Increased
Crystallinity. Broad peaks are indicative of the
nanocrystalline nature of species.
(YSZ)0.59Au0.10(MoS2)0.18C0.11
(YSZ)0.39Au0.31(MoS2)0.11C0.18
Synthesis at 150C Barely visible ZrO2 peak
Synthesis at 300C Increased ZrO2 peak
Typical Hardness 1 GPa
Typical Hardness 5 GPa
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Variable Environment Friction Results
Vary environment from dry nitrogen (lt1 RH) to
humid (40 RH) air 100 g load, 0.2m/sec sliding
speed
(YSZ)0.33Au0.34(MoS2)0.14C0.17
(YSZ)0.42Au0.31(MoS2)0.16C0.11
YSZ/Au/DLC/MoS2 coatings synthesized at 150C and
300C in cycling tests.
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Coating Life Friction Results
Investigation of c.o.f. in a humid environment
and dry nitrogen until break down. 100g load,
0.2m/sec sliding speed.
Dry nitrogen
Humid air
(YSZ)0.39Au0.31(MoS2)0.11C0.18 (CHM5)
(YSZ)0.34Au0.24(MoS2)0.17C0.24 (CHM1)
Samples did not break down!
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High Temperature Friction Results
Transfer Films Formed in 500 C Air
Au nano-grains nucleated on the surface
(YSZ)0.33Au0.14(MoS2)0.15C0.36
Au grains provide lubrication by shear deformation
200 mm

• Formation of gold-rich transfer film in friction
  contact by Au diffusion to the surface and
  nucleation of Au nano-grains.

• Provides friction coefficients at elevated
  temperatures within 0.10-0.25 range
• For up to 6000 cycles.

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Carbon vs. MoS2
Vary environment from dry nitrogen (lt1 RH) to
humid (40 RH) air 100 g load, 0.2m/sec sliding
speed.
(YSZ)0.41Au0.23(MoS2)0.35
(YSZ)0.39Au0.28C0.31
XPS High Resolution Carbon Peak. Sample CHM12
Indicates carbide formation
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Raman Analysis (YSZ)0.39Au0.31(MoS2)0.11C0.18
(CHM5)
Ball in Dry Nitrogen
Ball in Air 40RH
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Raman Analysis (YSZ)0.39Au0.31(MoS2)0.11C0.18
(CHM5)
Wear Track Dry Nitrogen
Wear Track Air 40RH
Wear tracks show mixture
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Raman Analysis (YSZ)0.32Au0.32(MoS2)0.15C0.19
(CHM10)
Ball in Air 40 RH
Ball in Dry Nitrogen
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Raman Analysis (YSZ)0.32Au0.32(MoS2)0.15C0.19
(CHM10)
Wear Track Dry Nitrogen
Wear Track Air 40 RH
Some mixing was found
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Summary of Results
5000 sliding cycles, 100g load, 0.2 m/sec sliding
speed.
Friction spikes occurred. Thickness data not
complete.
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Al2O3/Au/DLC/MoS2 Coatings
(Al2O3)0.40Au0.18(MoS2)0.20C0.19
(Al2O3)0.40Au0.18(MoS2)0.20C0.19
Wear Track 5k cycles dry nitrogen then 5k cycles
air. Nanoindentation sample hardness 4.3 GPa.
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Summary of Results
5000 sliding cycles, 100g load, 0.2 m/sec sliding
speed.
Friction spikes occurred. Extended run-in.
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Summary and Conclusions

• Chameleon coatings of YSZ/Au/DLC/MoS2 and
  Al2O3/Au/DLC/MoS2 have been synthesized
• The coating systems show excellent tribological
  adaptability to cycling in high and low humidity
  environments.
• Some degree of chemistry adaptation has been
  found but more research is necessary. MoS2 may be
  doing the bulk of the work.
• Au in the nanocomposites is valuable for high
  temperature applications and perhaps may be
  valuable in aiding MoS2.

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Publications in Progress and Future Work

• More work on optimizing Al2O3/Au/DLC/MoS2.
• Ascertain the actual role of Carbon and MoS2 in
  both systems.
• Novel high temperature system, Rhenium/Al2O3/BN.

• Papers 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.
• C.C. Baker, R.R. Chromik, K.J. Wahl, and A.A.
  Voevodin, Synthesis of Al2O3/Au/DLC/MoS2
  nanocomposite coatings for Space and Ambient
  Environments.

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Acknowledgements

• This work has been supported by AFOSR MURI grant
  FA9550-04-1-0381
• Dr. Andrey Voevodin
• Dr. Jeff Zabinski
• Prof. Jacqueline Krim
• Dr. Richard Chromik, Naval Research
• Laboratory
• Dr. Kathy Wahl, Naval Research Laboratory
• Dr. Jianjun Hu
• Dr. Chris Muratore