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Friction control through solid lubricant films Jens Hardell, Braham - - PowerPoint PPT Presentation
Friction control through solid lubricant films Jens Hardell, Braham - - PowerPoint PPT Presentation
Friction control through solid lubricant films Jens Hardell, Braham Prakash Lule University of Technology, Sweden jens.hardell@ltu.se Outline Introduction to solid lubricants Molybdenum disulphide Burnished MoS 2 films Sputtered MoS 2 -Ti
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Introduction to solid lubricants
What is a solid lubricant?
- An easily sheared solid material that reduces mechanical
interaction and friction between two contacting surfaces under normal load and relative sliding
- Examples of common solid lubricants:
Layered lattice or lamellar Polymers Soft metals Oxides MoS2 PTFE Au MoO3 WS2 Nylon Ag PbO Graphite Sn
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Introduction to solid lubricants
Solid lubricant
Anisotropy Adhesion to substrate Electrical conductivity Volatility Thermo-chemical stability Hardness Cohesion
Some desirable properties of a solid lubricant:
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Introduction to solid lubricants
Why use solid lubricants?
- Extreme operating conditions
Atmospheric pressure Vacuum pressure, Pa 102 1 10-2 10-4 10-6 10-8
Liquid lubricants and greases
Solid lubricants High vacuum
150 200 250 300 500 Room temperature Temperature, °C
Liquid lubricants
Solid lubricants High temperature
Greases
Temperature, °C
- 100
- 273
Liquid lubricants and greases
Solid lubricants Low temperature
Radiation dose, rads
Liquid lubricants and greases
Solid lubricants Radiation
105 106 107 108 109 1010
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Introduction to solid lubricants
Examples of applications
Self lubricating bearings Space applications Machining tools
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Molybdenum disulphide
www.machinerylubrication.com
- Naturally occurring mineral
- Lattice layer structure
- Low friction is achieved through:
– Good adhesion to substrate – Weak VdW bonds – Large separation distance between adjacent lamellae
Pros Cons
Vacuum Oxidation High loads Humidity High temperature
Strong covalent bonds between S and Mo Weak VdW bonds between lattice layers Mo S S
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Burnished MoS2 films
- A. K. Kohli, B. Prakash, Tribology Transactions 44 (2001) 147-151
AISI 304 Stainless steel
- Sand blasted
High purity powder (OKS 110)
- Average particle size: 0.6-0.8 μm
- Max. particle size: 15 μm
- Abrasive impurities: Insignificant
Flat plate Disc specimen MoS2 powder Figure eight pattern FR FR FN Materials and film preparation Test setup
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Burnished MoS2 films
- A. K. Kohli, B. Prakash, Tribology Transactions 44 (2001) 147-151
Effect of temperature on friction
Influence of temperature and momentary water vapour input on the frictional behaviour
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Sputtered MoS2-Ti films
- J. Hardell, I. Efeoğlu, B. Prakash, Tribological degradation of MoS2-Ti sputtered coating
when exposed to elevated temperatures, To be communicated
MoS2 Ti MoS2 MoS2 Closed Field Unbalanced Magnetron Sputter Ion-plating MoS2-Ti Ti Tool steel Tribological tests Bearing steel ball Tool steel with self-lubricating coating
FN FR FR FN ω
Bearing steel ball Tool steel with self-lubricating coating
MoS2 is co-sputtered with Ti to improve wear resistance, resistance against oxidation and humid environments and hardness of the coating
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Sputtered MoS2-Ti films
- J. Hardell, I. Efeoğlu, B. Prakash, Tribological degradation of MoS2-Ti sputtered coating
when exposed to elevated temperatures, To be communicated
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 200 400 600
Time [s]
Coeffcient of friction 10 20 30 40 50 60 70 80 90 100 Load [N]
Friction Load
MoS2-Ti coatings shows load dependent coefficient of friction Reciprocating sliding tests at 25% RH, 0.1 m/s and 50 N
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Sputtered MoS2-Ti films
- J. Hardell, I. Efeoğlu, B. Prakash, Tribological degradation of MoS2-Ti sputtered coating
when exposed to elevated temperatures, To be communicated
Reciprocating sliding tests at 25% RH , 0.1 m/s and 50 N
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1 10 100 1000 10000
Time [s]
Coefficient of friction
40C Preheated 30min 400C
Increased friction and reduced life of coating after exposure to elevated temperature
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Sputtered MoS2-Ti films
- J. Hardell, I. Efeoğlu, B. Prakash, Tribological degradation of MoS2-Ti sputtered coating
when exposed to elevated temperatures, To be communicated
Unidirectional sliding tests at 40% RH , 0.2 m/s and 50 N Friction is increased and “spikes” appear sooner when exposed to elevated temperature
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Sputtered MoS2-Ti films
- J. Hardell, I. Efeoğlu, B. Prakash, Tribological degradation of MoS2-Ti sputtered coating
when exposed to elevated temperatures, To be communicated
Ball Disc Surface damage
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Concluding remarks
Burnished MoS2 films:
– Coefficient of friction is load and temperature dependant – Exposure to moist air increases friction momentarily
Sputtered MoS2-Ti coatings:
– Coefficient of friction is load and temperature dependant – Increased humidity leads to increased friction – After exposure to elevated temperature, the MoS2-Ti coating experiences reduced life and induces higher wear on the counter body
Application of solid lubricants
– Can be an effective way to control friction and reduce wear in certain applications – For successful implementation it is important to keep in mind factors like environment, load, speed, lifetime of component etc.
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