Study On Preparation, Characterization And Tribological Properties Of Ti₃Si And Ti₃SiC₂ Nanomaterials

Ti3Si nanoparticles with new crystal structure were prepared by mechanical alloying (MA) process. The microstructure and morphology were investigated by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The tribological properties of Ti3Si nanoparticles as additives in the base oil were also investigated.In addition, n-hexane (C6H14) was added into Ti-Si-C ternary powders before mechanical alloying, in order to reduce the energy barrier of reaction and then mixed with Al and NaCl as sintering additives to reduce reaction conditions. So, high purity Ti3SiC2 powders were prepared; Hexagonal nano-laminated Ti3SiC2 were synthesized successfully by spark plasma sintering, hot pressing, vacuum sintering and pressureless sintering respectively. The reaction mechanism of Ti3SiC2 and crystal growth mechanism were studied. The tribological properties of nano-laminated Ti3SiC2 as lubricating oil additives were also investigated.The main content comes as following:(1) The mechanical alloying process caused the amorphous alloy to crystallize. Based on the analysis of the XRD pattern the peaks of the sample were indexed and the possible atom arrangement in the unit cell was given. The microstructure is confirmed by HRTEM and SEAD that agreed with the theoretical calculations.(2) The tribological properties of Ti3Si nanoparticles were investigated on friction and wear tester, and the wear mechanism was also discussed. Investigation results showed that Ti3Si nanoparticles were excellent lubricating oil additive in point of anti-friction and anti-wear property. In the fluid lubricating area, the Ti3Si nanoparticles reacted as the micro-rolling section, so the sliding friction became rolling friction. Ti3Si nanoparticles were cracked in the boundary lubricating area, and the Ti interior of kernel smooth planking on the wear scar surface of the test balls. It can be inferred that the nanoparticles have been deposited on the surface of the wear scar and filled into the tiny grooves, where after these particles act as a barrier, separating the friction surface pair, reducing the wear, and subsequently postponing the occurrence of seizure. The mixed lubricating area is a transition area. The mechanism is the micro-rolling function take as the primary near the fluid lubricating area and smooth planking acted primarily closing the boundary lubricating area.(3) Spark plasma sintering of nano-laminated Ti3SiC2. The results showed that:The spark plasma sintering process can significantly reduce the synthesis temperature of Ti3SiC2 with the combination of Al and NaCl as additives. The sintering temperature for synthesis of high purity and dense Ti3SiC2 is 100℃～300℃lower than conventional sintering process.(4) Pure nano-laminated Ti3SiC2 materials were synthesized by hot pressing from Ti, Si, C and Al powders with NaCl additive in argon at 1250℃. A mount of standard hexagonal geometry of the flake grain were founded on the Ti3SiC2 particles, which exhibit a clear and well-defined laminated structure and smooth surface of hexagonal growth layers. The thinnest of layers is up to 5nm which belonged to nano-level.(5) Pressureless sintering of nano-laminated Ti3SiC2. A large number of independent hexagonal flakes of Ti3SiC2 were founded in samples that were different from lamellar stacking Ti3SiC2 synthesized by hot pressing in morphology.(6) The growth mechanism of Ti3SiC2 crystals controlled by two-dimensional nucleation was put forward. The growth pattern of layered steps implies that the growth of the (002) face should undergo two steps, the intermittent two-dimensional nucleation and the continuous lateral spreading of layers on growth faces. According to the Donnay-Harker theory, the crystalline shape of TSC is determined by the relative growth rate of the (002), (100) and (101) faces.(7) The tribological properties of nano-laminated Ti3SiC2 materials were investigated on friction and wear tester. Investigation results showed that nano-laminated Ti3SiC2 materials were excellent lubricating oil additive in point of anti-friction and anti-wear property. Ti3SiC2 nanosheets played well a role in filling repair in the friction process, thereby preventing the further deepening furrow, avoiding the contact area decreases, and the reduced pressures between the friction pairs protected the material surface.