Design of self-lubricant materials Manu Tenhunen

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

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

Dry-lubricants Most common: –Graphite –Molybdenum disulfide (MoS 2 ) –Hexagonal boron nitride (h-BN) Usually low friction is because of lamerral structure –Found if graphite

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)

Points to consider during design 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

Recent results on self-lubricant material research Jian Liang Li and Dang Sheng Xiong experimented with Ni-Cr-W-Fe –alloy adding C, MoS 2 and combination of both to add self-lubricant properties to the matrix Samples were made from powders with pressing and hot-pressing CompositeNi-20CrWFeSiCMoS 2 Density Hardness (HRC) Ni–Cr–W–Fe–C56 wt. % ,7528,4 Ni–Cr–W–Fe– MoS ,3827 Ni–Cr–W–Fe–C– 5MoS ,9541 Ni–Cr–W–Fe–C– 10MoS ,1046 Ni–Cr–W–Fe–C– 15MoS ,8648

Recent results on self-lubricant material research Combining both dry-lubricants provided low friction and wear rate for the whole temperature range

Recent results on self-lubricant material research 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

Recent results on self-lubricant material research  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

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 (MoS 2 ), hexagonal boron nitride (h-BN)