Tribological Properties And Lubrication Mechanism Of Graphene Layer On Copper Surface Under Sliding Electrical Contact

Tribological problems(strong adhesion and severe wear)and electrical contact problems(electrical open and unstable contact resistance)make unlubricated self-mated copper a challenge topic under high contact stress and low sliding speed.With combined merits of good electrical conductivity and lubricity,graphene offers a solution to above mentioned problems.In this thesis,GNP is deposited on T2 copper surface by two methods(drop casting and self-assembling)using 1 mg/m L graphene solution as source.The tribological property of GNP lubricated self-mated copper is investigated under non current-loading condition and current-loading condition.The lubricating mechanism and tribological failure mechanism are discussed.The tribological behavior of GNP lubricated self-mated copper is evaluated in hot air and effect of heat treatment on the tribological property is also included.The main results and conclusions are as follows:1.Homogeneous and island-like GNP can be deposited using self-assembling while heterogeneous GNP is deposited using drop casting.Disorder and defects are commonly found.2.Under high contact stress and low sliding speed,unlubricated self-mated copper suffers high friction coefficient,severe adhesive wear and transition of wear.That is: prow formation in the first stage;work hardening in the intermittent stage;rider wear in the final stage.Under the same condition,LP108 and Ga-In-Sn are poor lubricants.In the presence of GNP,adhesion is markedly inhibited with friction coefficient of 0.3 to 0.35 and mild wear.3.GNP on copper disk has better lubricity than GNP on copper pin.Polarity of pin and disk as well as current value has no obvious influence on the tribological property and contact resistance.Raman spectra indicate the increasing intensity of D-band and shift of D-band to lower wave number.4.By replenishing GNP on worn surface of unlubricated self-mated copper,wear transition from adhesive wear to mild wear(burnished surface)is observed.Friction coefficient is markedly reduced.5.GNP remains lubricious after two cycles in a cyclic temperature from room temperature to 100? in dry hot air(RH < 5%).6.Heat treatment at 100? has no obvious influence on the lubricity of GNP.Heat treatment at 400? deteriorates the tribological property of GNP under current-loading condition.7.In reference to self-lubricating composites(Ag-Mo S2 and Cu-Gr),friction coefficient of GNP is 0.1 higher.Wear debris can hardly be found for GNP lubricated self-mated copper.In addition,preparation of GNP is convenient and cost-effective.8.Copper disk with PS texture suffers tribological failure in less than 2 minutes under current-loading condition.In contrast,the wear lifetime of copper disk with PG texture can be as long as 330 minutes.The genesis of a filmy self-lubricating Cu-GNP composite is observed as a result of smearing and trapping of GNP on PG surface.The quick removal of GNP from the wear track of PS surface is responsible for the quick tribological failure.