Design of self-lubricant materials

Manu Tenhunen 3.12.2015

Self-lubricating material

Self-lubricating: “(of a machine, mechanism, etc) able to lubricate itself“

Lubricate: lowers friction, heat transferer, cleans dirt Self-lubricating bearing patented in the 40’s

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Design of self-lubricant materials

Two ways of making a material self-lubricating– Making a porous material and filling with lubricant– Adding a dry-lubricant layer on a material

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Dry-lubricants

• Most common:– Graphite

– Molybdenum disulfide (MoS2)

– Hexagonal boron nitride (h-BN)

• Usually low friction is because of lamerral structure– Found if graphite

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Applications

• Self-lubricant materials are used in applications where standard liquid lubricants can’t be used– High temperature range– High wear– Long life-time– Vacuum conditions– Corrosive/oxidating environment

• For example– NASA and space applications (long life-time and vacuum)– Paper & food industry (can’t contaminate food or paper)

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Points to consider during design

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• Sometimes you need to balance properties and try to find the optimal– Substance A lowers friction but is soft -> finding balance

between enough hardness and minimum friction

• Sometimes you need to combine many substances– One that lubricates in low and one that lubricates in high

temperature– One substance to provide low friction and one to provide wear

resistance

Creating a self-lubricant material

Spraying or applying a dry-lubricant paste

• Depositing a film of self-lubricant material (ALD etc)

• Incorporating dry-lubricants in to the materials matrix– Plasma and other spraying techniques– Sputtering, pressing, alloys etc.

• Making a porous material and filling it with lubricant

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Recent results on self-lubricant materialresearch

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• Jian Liang Li and Dang Sheng Xiong experimented with Ni-Cr-W-Fe –alloy adding C, MoS2 and combination of both to add self-lubricant properties to the matrix

• Samples were made from powders with pressing and hot-pressing

Composite Ni-20Cr W Fe Si C MoS2 DensityHardness

(HRC)Ni–Cr–W–Fe–C 56 wt. % 10 30 1 3 0 8,75 28,4Ni–Cr–W–Fe–

MoS2 54 10 30 1 0 5 8,38 27Ni–Cr–W–Fe–C–

5MoS2 46 10 30 1 3 5 5,95 41Ni–Cr–W–Fe–C–

10MoS2 41 10 30 1 3 10 7,10 46Ni–Cr–W–Fe–C–

15MoS2 36 10 30 1 3 15 7,86 48

Recent results on self-lubricant materialresearch

• Combining both dry-lubricants provided low friction and wear rate for the whole temperature range

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Recent results on self-lubricant materialresearch• Wang et al. made polyvinylchloride (PVC) harder and

more durable with adding multilayer graphene (MLG) into it

• Done by mixing PVC and MLG powders, melting, mixing again, squeezed into sheets and finally hot-pressing

• 5 sheets with 0.54, 0.72, 0.90, 1.08 and 1.80 wt-% of MLG

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Recent results on self-lubricant materialresearch MLG clearly added self-lubricant properties in to the

PVC matrix Wang et al. concluded that this could be a good way to

make cheap and durable plastic parts

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Summary

• Self-lubricant materials lubricates itself• Used in applications where standard lubricants can’t be

applied– More wear resistance, lower friction, withstands different

environments

• Can be done by different deposition and powder metallurgy methods

• Common materials– Graphite, molybdenum disulfide (MoS2), hexagonal boron nitride

(h-BN)

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