Preparation And Tribology Property Of Diamond Film On Silicon Nitride

Compared with the metal bearing,the ceramic bearing is characterized with high temperature resistance,low density,high hardness,low thermal expansion coefficient,good self-lubricating property and high corrosion resistance.However,due to its high fragility,ceramic material is difficult to fabricate which lead to high cost and low reliability.Moreover,it is difficult to improve the surface microstructure of the ceramic bearing when it was manufactured.In particular,some defects,such as holes,micro-cracks and harmful impurities can not be eliminated by some effective methods.The Surface preparation technology plays an important role in enhancing the performance of the ceramic bearing,which can be able to increase the wear resistance,reduce friction coefficient and extend the service life of the bearing.Therefore,it is essential to study the process of the coating bearings to access better performance.In this thesis,diamond films were deposited on the surface of silicon nitride and silicon carbide ceramics by microwave plasma method.The surface morphology,surface composition and tribological properties of diamond films were studied.Main contents of this article are as follows:1.The CVD diamond films were deposited on silicon nitride ceramic and silicon carbide ceramics with different parameters.Micro-crystalline diamond films,nano-crystalline diamond films and diamond/graphite composite films were prepared on both substrates by microwave plasma CVD(MPCVD).The grain size range of micro-crystalline diamond film is about 200-300 nm,and the nano-crystalline grains appear at the grain boundary.With the increase of the volume fraction of methane,the particles on the diamond surface decrease and the nano-crystalline diamond is obtained.The linear diamond structure appears when the volume fraction of methane is further increased.2.The scanning electron microscopy(SEM),Raman spectroscopy and atomic force microscope are adopted to study the characterization of the deposited diamond films.The results showed that with the volume fraction of methane increasing,the surface roughness and contact angle decrease first,then increase,and then decrease again,and the surface grain size decreases.3.The friction and wear properties of diamond films deposited on Si3N4 ceramics under dry friction condition were studied by using,"ball-on-plate" reciprocating friction and wear tester.The results show that the diamond films prepared with the appropriate parameters have the best overall properties,the lowest friction coefficient and the lowest film wear rate.The content of graphite in the CVD film has a great influence on the friction and wear properties.In the films with low graphite content,the friction pairs show more wear and tear,and the furrow effect is more obvious.Micro-fracture of the surface diamond grain is the major form of wearing.With the increase of the graphite content,the hardness of film is reduced,and the dominant form of wear for the film was the rubdown of diamond grain.If the volume fraction of methane reach 10%,the wear scar show cliff-like interface,and brittle fracture was the major wear form.