Preparation And Tribological Properties Of Copper Matrix Composites With NbSe₂ Self-lubricating Materials

Self-lubricating(SL) materials exhibit superior performances especially in many cases with a little oil or without oil.Copper(Cu) matrix SL composite,as one of the most important metal matrix SL composites,is widely used owing to its excellent tribological properties,oxidization resistance and corrosion resistance etc.Recently,the graphite/MoS₂/Cu composites are the typical sliding electric contact materials,applied in conducting the electric currents between the fixed parts of electric generator and the rotating components widely.But these composites have the following problems:the MoS₂ had the high electrical resistivity and inferior electrical conductivity;the graphite and MoS₂ were more ductile,which decreased the load capacity,wear resistance properties and welding resistance of the electric contact materials.With the development of all kinds of electrical instruments into miniaturization,large voltage and current,high speed,the electric contact materials were required to have large critical linear velocity,large carrying capacity,low contact voltage,low friction coefficient,low wear loss,but these properties of the graphite/MoS₂/Cu composites were difficult to meet the above requirements.However,NbSe₂ with the similar crystalline structure and tribological properties of MoS₂,but the electrical resistivity is only 10^-4Ω.cm that six amount levels less than that of MoS₂,one less than the graphite.NbSe₂ had not only anti-friction and wear resistance,but also improved the mechanical properties of the composites.Meanwhile, the anisotropy of NbSe₂ improved the electrical conductivity and commutating capability.So far the research into NbSe₂-copper(Ag) composites has much focused on the layered structure(such as sheets),the tribological properties of the NbSe₂ nanofiber has not been reported.In the thesis,the bronze was selected as the matrix,and nano-NbSe₂ materials with appropriate size and quantity was added as the solid self-lubricant.The copper matrix composites with NbSe₂ nanofiber of low electrical resistivity and excellent anti-friction and wear resistance properties were successfully fabricated by powder metallurgy.The results showed that the combination of the interfaces between matrix and nano-NbSe₂ materials was affected by the high temperature sintering process. After the wear and friction tests,the micro-structures,fracture morphologies,worm surfaces,composition and morphology of debris of the composite samples were analyzed by SEM(scanning electron microscope),XRD(X-ray diffraction), EDS(energy dispersion spectrometer),respectively.The wear behaviors and mechanisms were investigated in detail in the room temperature.During the wear tests,nano-NbSe₂ materials were pressed and moved to surface,and then gradually deformed into continuous thin solid lubricating film.The so-formed film was tightly adhered on the friction surfaces and caused good anti-friction.The main contents are following:(1) NbSe₂ nanofibers or sheets were obtained by heating sealed quartz ampoules by mixed Se and Nb in high temperature boxed furnace.Besides,the mixture of Se and Nb powders were milling in high energy ball-milling machine,the mixture after milling were heat in tubular furnace,a lot of NbSe₂ nanoparticles produced.The component and microstructure of NbSe₂ were investigated by means of X-ray diffraction(XRD),scanning electronic microscope(SEM) and transmission electronic microscope(TEM).(2) NbSe₂ nanofibers or sheets were mixed with bronze power uniformity,then copper composites sintered materials with NbSe₂ nanoparticles were prepared by a process of powder metallurgy.The friction and wear performance of composites were investigated by UMT-2 Multi-specimen test system.It was found that the incorporation of NbSe₂ nanoparticles contributed to effectively steady the friction coefficients under all kinds of loads and improve the antifriction performance of the composites,which was attributed to the self-lubricity of the NbSe₂ nanoparticles lubricating film formed on the worn composite surface,and NbSe₂ nanofibers as solid lubricants is improving the tribological properties better than NbSe₂ sheets in the copper-base composites.The friction mechanism of lubrication was discussed preliminary based on the analysis of experiment data and microstructure of NbSe₂ nanoparticles.The lubrication has excellent tribological properties may be due to the following factors:unique closed structures,lubrication films and fill up-repair.