Study On Preparation And Tribological Properties Of Ti₃SiC₂Reinforced By Carbon Fibers Or Carbon Nanotubes

is a remarkable ternary layered compound with excellent comprehensive performances, which combines many best properties of both metal and ceramic, such as high thermal conductivity, good resistance to corrosion and oxidation, easy machinability and nice self-lubricating. However, to some extent, it possesses low hardness and shear strength, poor wear resistance, which limits the application fields of Ti3SiC2as a solid self-lubrication material severely. Carbon fibers (CFs) or carbon nanotubes (CNTs) as reinforcement phase are utilized with Ti3SiC2powders to fabricate Ti3SiC2composites with high hardness, good wear resistance and excellent self-lubricating so as to improve mediocre hardness and wear resistance of Ti3SiC2material.In this paper, from the point of improving interface bonding between CFs or CNTs and Ti3SiC2, the processes of coating CFs and CNTs with TiC plating and fabricating Ti3SiC2by vacuum sintering method are discussed. CFs-Ti3SiC2and CNTs-Ti3SiC2composites are synthesized by spark plasma sintering (SPS) technology. Moreover, this research also contains studies on tribological properties, mechanisms establishment of friction&wear and self-lubrication of the composites.Firstly, this precoating powder is prepared by Ti, TiH2powders and hydrochloric acid solution (30%). Utilizing the precoating powder, CFs and CNTs are coated with TiC plating by vacuum slow vapor deposition technology, and the effects of soaking temperature and time on coating are discussed. The optimal process of coating is850℃for2hours with a heating rate of15℃/min and under a vacuum degree of6.0×10-2Pa. By this method, the coating of CFs or CNTs is close, intact and uniform. And then, Ti3SiC2with purity of99.9wt.%is fabricated, under a vacuum degree of6.0×10-2Pa, from mixture powders of4.05Ti/2SiC/1TiC/0.2A1(molar ratio) at1280℃for2hours with a heating rate of15℃/min.Furthermore, CFs-Ti3SiC2and CNTs-Ti3SiC2composites are synthesized from mixture powders of TiC coated CFs or CNTs and Ti3SiC2with a certain proportion by SPS process at1200℃for10min. Phase composition, microstructure, relative density, surface hardness of composite samples is investigated. The research indicates that the compactness of these two composites is good; and the addition of CFs decreases surface hardness of Ti3SiC2, while the addition of CNTs improves surface hardness of Ti3SiC2. Finally, friction and wear tests are conducted for the composite samples matching with GCrl5steel balls as friction pairs. This experimental research demonstrates that CFs(8wt.%)-Ti3SiC2and CNTs(3wt.%)-Ti3SiC2samples possess preferable tribological properties, in addition their friction coefficients and wear rates are0.78,6.47×10－5mm3(Nm)－1and0.40,1.80×10－4mm3(Nm)－1, respectively. Compared to pure Ti3SiC2sample, CFs(8wt.%)-Ti3SiC2has higher friction coefficient and lower wear rate, and CNTs(3wt.%)-Ti3SiC2performs both lower friction coefficient and smaller wear rate. In conclusion, tribological properties of Ti3SiC2composites are improved obviously by CNTs as reinforcement. By investigations on microstructures and energy spectrums of composite sample worn surfaces, steel ball worn surfaces and wear debris, the conclusion that the wear mechanism of CFs(8wt.%)-Ti3SiC2is oxidation wear with adhesive wear and this of CNTs(3wt.%)-Ti3SiC2is oxidation wear with fatigue wear is draw.These investigation results would be very meaningful to preparing self-lubrication composites with excellent properties, investigating friction&wear mechanisms, and building self-lubrication models.