L15 Friction
Content
Lecture 15 Tribological Characterization
Tribology
The science and technology of interacting surfaces in relative motion: The study of lubrication, adhesion, friction, and wear between contacting surfaces
It impacts national economy of all nations and lifestyles of most people
New materials and coatings Can lower friction and reduce wear, and thus can have a positive impact on future tribological systems
Economic Impact of Tribology
• Economic Losses in U.S. due to inadequate control of friction and wear • Worldwide, it is estimated that 1/3 to 1/2 of world’s energy production is used to combat friction and wear (A. Z. Szeri,
Tribology: Friction, Lubrication, and Wear; Hemisphere Publishing, 1980, p.2)
Loss Material Wear Friction
Cost(b$) 100 100 70
•
When lost-labor, down-time, cost of replacement parts added, these figures may double. Latest Overall Estimates: $500B
P. Cummins/ORNL
•
Therefore, even very small improvements in energy efficiency (friction) and durability (wear) can save billions of dollars. Friction has a direct impact on environmental cleanliness as well.
Tribological Characterization: Scale of Test Methods
Mostly Simulations AFM, FFM Microtribology Machines Pin-on-disk
Atomic Scale Contacts
Molecular Debris
single asperity or nano-contact
microsystem domain engineering surfaces
1Å
cm-m
FR
M. Dugger
J. Che, et al., CalTech
fd
ATOMIC/NANOSCALE TEST METHODS
Examples of Atomic Scale Studies/Simulations
Atomic Scale Studies
Molecular Debris
single asperity or nanotribology
Multiple-asperity contact: microsystem domain
engineering surfaces
Work by Motohisa Hirano and others both theoretically simulated and experimentally demonstrated superlubricity (or frictionless sliding) between sliding pairs of Si(001) and a W (011) tip in ultra-high vacuum, (PRL, 78(1997)1448)). Also see, Socoliuc, et al., “Entering a new Regime of Ultralow Friction”, PRL, 92(2004)134301.
Commensurate STM of one layer of graphite Incommensurate Dry N2
µ ~ 0.001
Dienwiebel et.al.,
2D/2D
Tribolever
PRL, 92(2004)126101
Tribological Characterization at Nanoscales
AFM Tips
Surface Characterization of Diamond Films by AFM vs SEM
AFM SEM
AFM
SEM
AFM/FFM/SFM
Position Sensitive detector
Nano Wear Tests with Carbon Overcoats
FCA N: 0 at% FCA N: 8 at% FCA N: 16 at%
Sputtering
pCVD
Load: 10 μN ×12 scan
FCA: Filtered Cathodic Arc
X: 0.5 μm/div. Z: 20 nm/div.
Durability
・ Pin: Al2O3-TiC ball (2 mmφ) ・ Applied load: 10 gf ・ Sliding velocity: 0.2 m/s
Rotational pass number 10000 8000 6000 4000 2000 0 0 5 10 15 20 Carbon Thickness (nm)
pCVD Sputtering FCA
Observation of stick-slip on gold
A 5x5 nm2 atomic scale friction measurement on Au(111) at 4x10-10 Torr at room temperature. The atomic lattice of gold causes stick-slip friction to occur with the periodicity of the lattice. The inset line trace shows the clearly resolved stick-slip features for the forward and backward traces.
From R. Carpick/U. Wisconsin
Friction Force Maps
700nm x 700nm image of a few nanometer flat carbon islands on a magnetite single crystal. "Material dependend friction contrast" in the right image is due to more or less adsorbates between carbon islands (lower friction) and magnetite (higher friction). (Images taken by Stefan Müller)
Nano-to-micro Scale Test Machines
Contact Geometry
Courtesy of G. Sawyer
Nano/Macrotribology of DLC Films
0.8 0.6 0.4
friction coefficient
0.2 0
0
-0.2 -0.4 -0.6 -0.8
50
100
150
200
250
300
350
time (seconds)
Courtesy of G. Sawyer
TRIBOLOGICAL CHARACTERIZATION AT MESO/MACRO-SCALES
Tribological Characterization:
Typical contact Geometries for Macroscale Experiments
•There are so many contact configurations to chose from. •Each geometry is very unique and designed to simulate an application. •Test conditions may vary a great deal, depending on the contact geometry. •Some of them are standardized and require the certain procedures to follow.
Pin-on-disk Machines
Load
Coating
Sapphire Ball
Disk
Load: 1 - 20 N Speed: 0.3 - 1 m/s Environment: Dry Nitrogen Ball Radius:3.175 - 5 mm
Contact geometry
Operating principles
Operating Principles
• • In most cases, friction and wear data. Friction coefficient, µ = Ff / Fn (where, Fn is the normal force)
Wear rate in the ball and in the flat Friction coefficient
Wear Volume on ball: Wb=πd4/64r (d:wear scar diameter, r: ball radius) Wear Rate=Wb/LN (N: Normal force; L:Sliding distance)
Other Popular Machines
Four Ball Machine Block-on-ring test machine
High-temperature Foil bearing test machine
Twin-disk rolling/sliding machine
Reciprocating Test Machine
• Major Test Variables – Time, Speed (rpm), Track Radius – Load / Stress – Material Composition (Pin/Ball & Flat) – Coating Composition – Test Environment (Dry, Inert, RH), Lubricant (& Additive) Composition and Rheological Properties Test Output – Continuous Friction & Temperature Data
•
Typical Contact Geometries
Courtesy of G. Fenske
Low-Amplitude Reciprocating (Fretting) Test Machine
• Issue - performance of SIDI components at higher pressures with low-lubricity fuels
Injector Wear
5.E-08 5.E-08 4.E-08 4.E-08 3.E-08 3.E-08 2.E-08 2.E-08 1.E-08 5.E-09 0.E+00
D ry
Diamonex-HT Uncoated Balzers Diamonex STD NFC-6
as G
Coating
NFC-2
E8 5 ha Et l no
Wear Rate (mm^3/N-m)
85 M
in ol e
Fuel
Courtesy of J. Hershberger
Images of Rubbing Surfaces
3D-Pin Surface 3D-Disk Surface
2D Images Of Pin Surfaces
THE RANGE OF TRIBOLOGICAL PROCESSES TO CONSIDER WHILE TESTING COATED SURFACES
MATERIAL INPUT Macromechanical GEOMETRY: Micromechanical changes Macrogeometry changes Topography Loose particles Tribochemical Fluids, environment changes PROPERTIES: Chemical composite. Microstructure Shear strength Elasticity Viscosity ENERGY INPUT Velocity Temperature Normal Load Tangential force MATERIAL OUTPUT GEOMETRY: Macrogeometry Topography Loose particles Fluids, environment PROPERTIES: Chemical composition Microstructure Shear strength Elasticity Viscosity ENERGY OUTPUT Friction Wear Velocity Temperature Dynamics
Courtesy of K. Holmberg, VTT/Finland
lon9706
Material transfer
Tribo-induced failure modes
Hogmark 01
Initial state
Coating detachment
Cracking & spalling
Coating & substrate deformation
Coating & substrate deformation + fracture
Transfer from the counterface
Gradual coating wear
Initial gradual wear + premature detachment
Coating detachment + substrate wear
Premature failure
Failure due to gradual wear
Courtesy of C. Donnet
Friction and Wear Mechanisms
Macro mechanisms
Micro mechanisms Transfer
Tribochemistry
Nano mechanisms
Holmberg 01
Courtesy of C. Donnet
Macro-mechanisms
Main parameters
• Mechanical properties (H, E, stress) • Thickness of the coating • Surface roughness • Debris Principle of load-carrying capacity
TiN/Steel
Hogmark 01
Lee 98
Quantification by scratch test
Courtesy of C. Donnet
Micro-mechanisms
Material response at the µm scale
• Stress and strain at the asperity level • Crack generation and propagation • Material release & Particle formation
Electroless Ni coating / gear
Hogmark 01
TiN / HSS
Hogmark 01
Courtesy of C. Donnet
Holmberg 01
Energy accommodation modes
Micro Stress Distribution on a Coated Surface
Hogmark et al.
Ways to Improve Load Carrying Capacity of Coatings
Hogmark et al.
Summary of Wear Mechanisms FRICTION MECHANISMS in Coated Surfaces
COATED CONTACT HARDNESS OF COATING
a HARD SLIDER
SOFT HARD b c
HARD SOFT d
THICKNESS OF COATING
PLOUGHING SHEARING LOAD CARRIED BY COATING STRENGTH g h SUBSTRATE DEFORMATION
e
f
SURFACE ROUGHNESS
SCRATCHING PENETRATION REDUCED CONTACT AREA & INTERLOCKING ASPERITY FATIGUE
DEBRIS
PARTICLE EMBEDDING PARTICLE PLOUGHING PARTICLE HIDING PARTICLE CRUSHING
Courtesy of K. Holmberg/VTT-Finland
lon9708
ETM - - KGH\TCB\FRICTM97.dsf.
i
j
k
l
MAJOR SOURCES OF FRICTION
Physisorption/chemisorption
Roughness
H2O
OH
O
Major Causes of Friction
Adhesion
Capillary Forces
Elastic/plastic Deformation
Real Contact Areas
Deformation
Adhesion Mechanisms of Friction
The Case of Carbon Films - Covalent sigma (the strongest) - Ionic - Metallic Not applicable to carbon - Magnetic N -π-π* Attraction (in F the case of graphite) - van der Waals -Electrostatic -Capillary A2 A
1
van der Waals
Capillary
Ar = A1 + A2 + . . . Ff = σ.Ar
Electrostatic
Transfer Films vs Friction
• Transfer formation : run-in phenomena + COF fluctuations • Transfer film (0.01 - 50 µm) “Repartition” of the lubricant reservoir • Interfilm sliding : general condition of steady-state • Wear not linear versus duration Accommodation modes Transfer formation Interfilm sliding
Donnet 01
Singer 92
PTFE & Polyimide TiN, CrN, (Ti,Al)N MoS2 DLC
Yamada 90 Huang 94, Wilson 98 Fayeulle 90, Wahl 95 Ronkainen 93, Donnet 95, Grill 97
Effect of Transfer Film Forming Tendency on Friction
DLC-coated Steel Disk Against Various Counterface Balls
0.25
Dry N2
Friction Coefficient
0.2
Zirconia Steel Sapphire DLC-Coated Steel
Sapphire
0.15
Zirconia
Transfer Film
0.1
0.05
DLC Coated Steel Ball
0
Uncoated Steel Ball
0
100
200
300
400
500
600
Coated Steel Ball
Distance (m)
Tribochemistry vs Friction
Friction-induced “fresh” surfaces Temperature increase Effect of the surrounding environment
Tribo-reactions at the nm scale
• Metal Jahanmir 89, Kuwano 90, Erdemir 91 • TiN, CrN, TiC, HBN Mäkelä 85, Gardos 89, Singer 91, Martin 92, Lin 96 • Oxides Blomberg 93, Gee 95, Erdemir 95, Prasad 97 • Various (Ti, Al, Zr, Si)N, Rebouta 95 • DLC Miyoshi 90, Ronkainen 90, Donnet 95, Erdemir 95, Voevodin 96, Grill 97, Fontaine 01 • Diamond, Graphite Gardos 90, Hayward 90, Langlade 94, Blanchet 94 • MoS2 Spalvins 80, Fleischauer 87, Singer 90, Martin 93, Wahl 95, Role of H2O on B2O3 Role of gaseous H2 on a-C:H films
1
(H=34at%)
1
0.1 0.01 0.001
10 hPa H2 µ=0.003
0 100 200 300 400 Number of cycles 500
0.1 0.01 0.001
µ=0.7 µ=0.007
0
UHV or Ar
Formation of lamellar boric acid
Erdemir 90-98
Donnet 01
100 200 300 400 Number of cycles
500
Tribochemical film Formation in Lubricated Contacts
300 µm 300 µm
Sture Hogmark
Steel/DLC EP
Stee/DLC EP
S W
30 µm
Fe O S W
30 µm
W
Fe O C
C
W
After 8000 cycles
C
at 700 N
Ni O W
Roughness vs Friction
F1 = W1 tan θ
W = W1 + W2 + . . . F = W tanθ
Tribology of Diamond Films
Roughness Effect
Erdemir, et al., Surface and Coatings Technology, 121(1999) 565-572
Roughness Effect on Friction
Diamond Films
MCD
Rough
Polished MCD
NCD
B. K. Gupta et al., J. Tribol., 116(1994)445.
Environment vs Friction
Physisorption/chemisorption
H2O
OH
O
0.8 0.7 Friction coefficient 0.6 0.5 0.4 0.3 0.2 0.1 0 0 50 100 150 200
Courtesy of J. Andersson Due to higher degree of covalent bond interactions Diamond Coated Ball
In water In air In argon
Initial friction is 0.1-0.2
Diamond Coated Disk
# Revolutions
Effect of Water Partial Pressure on Frictional Behavior of DLC Film
0.14
At 2000 Pa At 460 Pa At 0.4 Pa
Vacuum Experiments
0.12
0.1
Friction coefficient
?
0.08 0.06
0.04
Smoother and lower friction at lower water vapor pressures
0.02
0 0 20 40 60 80 100 120
Time (s)
J. Anderson and R. Erck/ANL
Environmental Sensitivity of MoS2 Type Solid Lubricant Coating
Work the best in dry, inert, or vacuum type environments
Base MoS2
Ti-Doped
Multiarc, Inc. data
The performance and durability of these solids are strongly affected by the presence of moisture and oxygen in the environment. Aging may also pose a major problem. Doping with Ti, Ni, Au, and Pb may reduce environmental sensitivity.
Friction Mechanisms of Soft Metals
Mainly because of their low shear strengths and rapid recovery as well as recrystallization, certain pure metals (e.g., In, Pb, Ag, Au, Pt, Sn, etc.) can provide low friction when present on sliding surfaces.
Most desired case
After Bowden and Tabor
Thickness of the film is very important
Selected References
• K. Holmberg and A. Matthews, Coatings Tribology: Properties, Techniques, and Applications in Surface Engineering, Elsevier, 1994. • B. Bhushan and B. K. Gupta, Handbook of Tribology: Materials, Coatings and Surface Treatments, McGraw-Hill, 1991. • B. Bhushan, Modern Tribology Handbook, Volumes I & II, CRC Press, 2000.
Tribology
The science and technology of interacting surfaces in relative motion: The study of lubrication, adhesion, friction, and wear between contacting surfaces
It impacts national economy of all nations and lifestyles of most people
New materials and coatings Can lower friction and reduce wear, and thus can have a positive impact on future tribological systems
Economic Impact of Tribology
• Economic Losses in U.S. due to inadequate control of friction and wear • Worldwide, it is estimated that 1/3 to 1/2 of world’s energy production is used to combat friction and wear (A. Z. Szeri,
Tribology: Friction, Lubrication, and Wear; Hemisphere Publishing, 1980, p.2)
Loss Material Wear Friction
Cost(b$) 100 100 70
•
When lost-labor, down-time, cost of replacement parts added, these figures may double. Latest Overall Estimates: $500B
P. Cummins/ORNL
•
Therefore, even very small improvements in energy efficiency (friction) and durability (wear) can save billions of dollars. Friction has a direct impact on environmental cleanliness as well.
Tribological Characterization: Scale of Test Methods
Mostly Simulations AFM, FFM Microtribology Machines Pin-on-disk
Atomic Scale Contacts
Molecular Debris
single asperity or nano-contact
microsystem domain engineering surfaces
1Å
cm-m
FR
M. Dugger
J. Che, et al., CalTech
fd
ATOMIC/NANOSCALE TEST METHODS
Examples of Atomic Scale Studies/Simulations
Atomic Scale Studies
Molecular Debris
single asperity or nanotribology
Multiple-asperity contact: microsystem domain
engineering surfaces
Work by Motohisa Hirano and others both theoretically simulated and experimentally demonstrated superlubricity (or frictionless sliding) between sliding pairs of Si(001) and a W (011) tip in ultra-high vacuum, (PRL, 78(1997)1448)). Also see, Socoliuc, et al., “Entering a new Regime of Ultralow Friction”, PRL, 92(2004)134301.
Commensurate STM of one layer of graphite Incommensurate Dry N2
µ ~ 0.001
Dienwiebel et.al.,
2D/2D
Tribolever
PRL, 92(2004)126101
Tribological Characterization at Nanoscales
AFM Tips
Surface Characterization of Diamond Films by AFM vs SEM
AFM SEM
AFM
SEM
AFM/FFM/SFM
Position Sensitive detector
Nano Wear Tests with Carbon Overcoats
FCA N: 0 at% FCA N: 8 at% FCA N: 16 at%
Sputtering
pCVD
Load: 10 μN ×12 scan
FCA: Filtered Cathodic Arc
X: 0.5 μm/div. Z: 20 nm/div.
Durability
・ Pin: Al2O3-TiC ball (2 mmφ) ・ Applied load: 10 gf ・ Sliding velocity: 0.2 m/s
Rotational pass number 10000 8000 6000 4000 2000 0 0 5 10 15 20 Carbon Thickness (nm)
pCVD Sputtering FCA
Observation of stick-slip on gold
A 5x5 nm2 atomic scale friction measurement on Au(111) at 4x10-10 Torr at room temperature. The atomic lattice of gold causes stick-slip friction to occur with the periodicity of the lattice. The inset line trace shows the clearly resolved stick-slip features for the forward and backward traces.
From R. Carpick/U. Wisconsin
Friction Force Maps
700nm x 700nm image of a few nanometer flat carbon islands on a magnetite single crystal. "Material dependend friction contrast" in the right image is due to more or less adsorbates between carbon islands (lower friction) and magnetite (higher friction). (Images taken by Stefan Müller)
Nano-to-micro Scale Test Machines
Contact Geometry
Courtesy of G. Sawyer
Nano/Macrotribology of DLC Films
0.8 0.6 0.4
friction coefficient
0.2 0
0
-0.2 -0.4 -0.6 -0.8
50
100
150
200
250
300
350
time (seconds)
Courtesy of G. Sawyer
TRIBOLOGICAL CHARACTERIZATION AT MESO/MACRO-SCALES
Tribological Characterization:
Typical contact Geometries for Macroscale Experiments
•There are so many contact configurations to chose from. •Each geometry is very unique and designed to simulate an application. •Test conditions may vary a great deal, depending on the contact geometry. •Some of them are standardized and require the certain procedures to follow.
Pin-on-disk Machines
Load
Coating
Sapphire Ball
Disk
Load: 1 - 20 N Speed: 0.3 - 1 m/s Environment: Dry Nitrogen Ball Radius:3.175 - 5 mm
Contact geometry
Operating principles
Operating Principles
• • In most cases, friction and wear data. Friction coefficient, µ = Ff / Fn (where, Fn is the normal force)
Wear rate in the ball and in the flat Friction coefficient
Wear Volume on ball: Wb=πd4/64r (d:wear scar diameter, r: ball radius) Wear Rate=Wb/LN (N: Normal force; L:Sliding distance)
Other Popular Machines
Four Ball Machine Block-on-ring test machine
High-temperature Foil bearing test machine
Twin-disk rolling/sliding machine
Reciprocating Test Machine
• Major Test Variables – Time, Speed (rpm), Track Radius – Load / Stress – Material Composition (Pin/Ball & Flat) – Coating Composition – Test Environment (Dry, Inert, RH), Lubricant (& Additive) Composition and Rheological Properties Test Output – Continuous Friction & Temperature Data
•
Typical Contact Geometries
Courtesy of G. Fenske
Low-Amplitude Reciprocating (Fretting) Test Machine
• Issue - performance of SIDI components at higher pressures with low-lubricity fuels
Injector Wear
5.E-08 5.E-08 4.E-08 4.E-08 3.E-08 3.E-08 2.E-08 2.E-08 1.E-08 5.E-09 0.E+00
D ry
Diamonex-HT Uncoated Balzers Diamonex STD NFC-6
as G
Coating
NFC-2
E8 5 ha Et l no
Wear Rate (mm^3/N-m)
85 M
in ol e
Fuel
Courtesy of J. Hershberger
Images of Rubbing Surfaces
3D-Pin Surface 3D-Disk Surface
2D Images Of Pin Surfaces
THE RANGE OF TRIBOLOGICAL PROCESSES TO CONSIDER WHILE TESTING COATED SURFACES
MATERIAL INPUT Macromechanical GEOMETRY: Micromechanical changes Macrogeometry changes Topography Loose particles Tribochemical Fluids, environment changes PROPERTIES: Chemical composite. Microstructure Shear strength Elasticity Viscosity ENERGY INPUT Velocity Temperature Normal Load Tangential force MATERIAL OUTPUT GEOMETRY: Macrogeometry Topography Loose particles Fluids, environment PROPERTIES: Chemical composition Microstructure Shear strength Elasticity Viscosity ENERGY OUTPUT Friction Wear Velocity Temperature Dynamics
Courtesy of K. Holmberg, VTT/Finland
lon9706
Material transfer
Tribo-induced failure modes
Hogmark 01
Initial state
Coating detachment
Cracking & spalling
Coating & substrate deformation
Coating & substrate deformation + fracture
Transfer from the counterface
Gradual coating wear
Initial gradual wear + premature detachment
Coating detachment + substrate wear
Premature failure
Failure due to gradual wear
Courtesy of C. Donnet
Friction and Wear Mechanisms
Macro mechanisms
Micro mechanisms Transfer
Tribochemistry
Nano mechanisms
Holmberg 01
Courtesy of C. Donnet
Macro-mechanisms
Main parameters
• Mechanical properties (H, E, stress) • Thickness of the coating • Surface roughness • Debris Principle of load-carrying capacity
TiN/Steel
Hogmark 01
Lee 98
Quantification by scratch test
Courtesy of C. Donnet
Micro-mechanisms
Material response at the µm scale
• Stress and strain at the asperity level • Crack generation and propagation • Material release & Particle formation
Electroless Ni coating / gear
Hogmark 01
TiN / HSS
Hogmark 01
Courtesy of C. Donnet
Holmberg 01
Energy accommodation modes
Micro Stress Distribution on a Coated Surface
Hogmark et al.
Ways to Improve Load Carrying Capacity of Coatings
Hogmark et al.
Summary of Wear Mechanisms FRICTION MECHANISMS in Coated Surfaces
COATED CONTACT HARDNESS OF COATING
a HARD SLIDER
SOFT HARD b c
HARD SOFT d
THICKNESS OF COATING
PLOUGHING SHEARING LOAD CARRIED BY COATING STRENGTH g h SUBSTRATE DEFORMATION
e
f
SURFACE ROUGHNESS
SCRATCHING PENETRATION REDUCED CONTACT AREA & INTERLOCKING ASPERITY FATIGUE
DEBRIS
PARTICLE EMBEDDING PARTICLE PLOUGHING PARTICLE HIDING PARTICLE CRUSHING
Courtesy of K. Holmberg/VTT-Finland
lon9708
ETM - - KGH\TCB\FRICTM97.dsf.
i
j
k
l
MAJOR SOURCES OF FRICTION
Physisorption/chemisorption
Roughness
H2O
OH
O
Major Causes of Friction
Adhesion
Capillary Forces
Elastic/plastic Deformation
Real Contact Areas
Deformation
Adhesion Mechanisms of Friction
The Case of Carbon Films - Covalent sigma (the strongest) - Ionic - Metallic Not applicable to carbon - Magnetic N -π-π* Attraction (in F the case of graphite) - van der Waals -Electrostatic -Capillary A2 A
1
van der Waals
Capillary
Ar = A1 + A2 + . . . Ff = σ.Ar
Electrostatic
Transfer Films vs Friction
• Transfer formation : run-in phenomena + COF fluctuations • Transfer film (0.01 - 50 µm) “Repartition” of the lubricant reservoir • Interfilm sliding : general condition of steady-state • Wear not linear versus duration Accommodation modes Transfer formation Interfilm sliding
Donnet 01
Singer 92
PTFE & Polyimide TiN, CrN, (Ti,Al)N MoS2 DLC
Yamada 90 Huang 94, Wilson 98 Fayeulle 90, Wahl 95 Ronkainen 93, Donnet 95, Grill 97
Effect of Transfer Film Forming Tendency on Friction
DLC-coated Steel Disk Against Various Counterface Balls
0.25
Dry N2
Friction Coefficient
0.2
Zirconia Steel Sapphire DLC-Coated Steel
Sapphire
0.15
Zirconia
Transfer Film
0.1
0.05
DLC Coated Steel Ball
0
Uncoated Steel Ball
0
100
200
300
400
500
600
Coated Steel Ball
Distance (m)
Tribochemistry vs Friction
Friction-induced “fresh” surfaces Temperature increase Effect of the surrounding environment
Tribo-reactions at the nm scale
• Metal Jahanmir 89, Kuwano 90, Erdemir 91 • TiN, CrN, TiC, HBN Mäkelä 85, Gardos 89, Singer 91, Martin 92, Lin 96 • Oxides Blomberg 93, Gee 95, Erdemir 95, Prasad 97 • Various (Ti, Al, Zr, Si)N, Rebouta 95 • DLC Miyoshi 90, Ronkainen 90, Donnet 95, Erdemir 95, Voevodin 96, Grill 97, Fontaine 01 • Diamond, Graphite Gardos 90, Hayward 90, Langlade 94, Blanchet 94 • MoS2 Spalvins 80, Fleischauer 87, Singer 90, Martin 93, Wahl 95, Role of H2O on B2O3 Role of gaseous H2 on a-C:H films
1
(H=34at%)
1
0.1 0.01 0.001
10 hPa H2 µ=0.003
0 100 200 300 400 Number of cycles 500
0.1 0.01 0.001
µ=0.7 µ=0.007
0
UHV or Ar
Formation of lamellar boric acid
Erdemir 90-98
Donnet 01
100 200 300 400 Number of cycles
500
Tribochemical film Formation in Lubricated Contacts
300 µm 300 µm
Sture Hogmark
Steel/DLC EP
Stee/DLC EP
S W
30 µm
Fe O S W
30 µm
W
Fe O C
C
W
After 8000 cycles
C
at 700 N
Ni O W
Roughness vs Friction
F1 = W1 tan θ
W = W1 + W2 + . . . F = W tanθ
Tribology of Diamond Films
Roughness Effect
Erdemir, et al., Surface and Coatings Technology, 121(1999) 565-572
Roughness Effect on Friction
Diamond Films
MCD
Rough
Polished MCD
NCD
B. K. Gupta et al., J. Tribol., 116(1994)445.
Environment vs Friction
Physisorption/chemisorption
H2O
OH
O
0.8 0.7 Friction coefficient 0.6 0.5 0.4 0.3 0.2 0.1 0 0 50 100 150 200
Courtesy of J. Andersson Due to higher degree of covalent bond interactions Diamond Coated Ball
In water In air In argon
Initial friction is 0.1-0.2
Diamond Coated Disk
# Revolutions
Effect of Water Partial Pressure on Frictional Behavior of DLC Film
0.14
At 2000 Pa At 460 Pa At 0.4 Pa
Vacuum Experiments
0.12
0.1
Friction coefficient
?
0.08 0.06
0.04
Smoother and lower friction at lower water vapor pressures
0.02
0 0 20 40 60 80 100 120
Time (s)
J. Anderson and R. Erck/ANL
Environmental Sensitivity of MoS2 Type Solid Lubricant Coating
Work the best in dry, inert, or vacuum type environments
Base MoS2
Ti-Doped
Multiarc, Inc. data
The performance and durability of these solids are strongly affected by the presence of moisture and oxygen in the environment. Aging may also pose a major problem. Doping with Ti, Ni, Au, and Pb may reduce environmental sensitivity.
Friction Mechanisms of Soft Metals
Mainly because of their low shear strengths and rapid recovery as well as recrystallization, certain pure metals (e.g., In, Pb, Ag, Au, Pt, Sn, etc.) can provide low friction when present on sliding surfaces.
Most desired case
After Bowden and Tabor
Thickness of the film is very important
Selected References
• K. Holmberg and A. Matthews, Coatings Tribology: Properties, Techniques, and Applications in Surface Engineering, Elsevier, 1994. • B. Bhushan and B. K. Gupta, Handbook of Tribology: Materials, Coatings and Surface Treatments, McGraw-Hill, 1991. • B. Bhushan, Modern Tribology Handbook, Volumes I & II, CRC Press, 2000.
