| Adding additives into oil to reduce friction and wear and even to mend the wornsurface has been widely applied in lubrication engineering for quite a long time.Although up to now, there are four generations of additives which have been createdor invented, the research and development of more effective additives have neverbeen ceased since all kinds of additives mentioned above are still not perfect,especially their effect of the wear repairing is far from satisfactory. Professionals inlubrication research field have been looking for the new materials to meet therequirement of repairing function to the lubricant additives all the time. In the past few years, the emergence of nano-materials has provided a newchoice for the development of lubricant additive. With the aid of nano-materials, a lotof novel work has been done with enormous encouraging achievements obtainedbecause the tribological properties have been enhanced obviously. As for themechanism of anti-wear and friction reduction, the following explanation has beenpredicted by most of professionals that the nano-particles act as spacer between thetwo friction surface, and some ever proposed that the nano-particles were rolling likea ball in the grinding area which leads to the reduction of friction coefficient, but nowmore and more people believe that nano-particles deposit on the friction surface andcompensate the loss of mass, the so-called mending effect. However, systematic workfor investigating the mechanism of the mending effect of nano-particles has rarelyperformed. In order to make further research of FR and AW mechanism, firstly themorphologies of metal nano-particles were observed by TEM and HRTEM, and theparticle size was measured by X-ray diffraction method. Also, the thermal propertywas investigated by TG-DTA equipment. For the purpose of clearly understanding FR and AW mechanism of metalnano-particles, first we need to know in what kind of lubricating state the FR propertywas operated, so we investigated the tribology property of metal nano-particles on thefriction and wear testing machine, and Stribeck curves were made on the basis oftesting data. After observing wear surfaces by SEM and analyzing morphologies ofnano-particles by TEM, we made an in-depth discussion of FR mechanism in differentlubricating state. The analysis result shows that metal Al particle acts as a ball rollingin the Hydro Dynamic Lubrication state and acts as spacer in the BoundaryLubrication state to achieve the FR effect. The mechanism of surface mending effect holds the fundamental position in thetheory of nano-tribology, therefore it should be made clear prior to the further practiceof the utilization of nano-material in the lubrication application. The thesis studies themending effect of nano-copper and nano-iron particles added to lubrication oil. Thewear surfaces were investigated by SEM, STM and EDS, and a heat-simulationexperiment was also made. The mechanism of mending effect was put forward thatmetal nano-particles partially melted when it contacted with friction surface and thendeposited on it. Moreover, the AW and EP properties of lubricant oil added with Al, Sn andAl+Sn nano-particles were tested by the four-ball machine. The friction surfaces wereinvestigated by SEM and EDS. Then, the AW and EP mechanism of metalnano-particles was advanced and explained that Sn powder deposits on the frictionsurface under low pressure and acts as AW additive; Al powder deposits on thefriction surface under high pressure and acts as EP additive.
|
PDF Full Text Request