Research On Synthesized, Reaction Mechanism Of 3Ti-Si/Al-2C-based Superhard Composites By SHS

With unique structure, Ti₃ Si C2, Ti₃ Al C2 combine properties of metallic and ceramic simultaneously, such as, low density, high melting point, good performance of conductivity and thermal conductivity, excellent oxidation resistance, thermal shock resistance and corrosion resistance, good machinability. Self-propagating hightemperature synthesis（SHS） is a new technology, which has the advantages of simple equipment process and energy-efficient. This research combine the both advantages,to study the synthesized, reaction mechanism of 3Ti-Si/Al-2C-based diamond/CBN composites by SHS, to discuss the influence of binder of starting materials, raw materials and abrasive concentration to the phase composition and microstructure, thermodynamics process and performance of prepared composites.Firstly, SHS was used to synthesize 3Ti-Si/Al-2C-based superhard composites from the mixtures of Ti/Si/C, Ti/Ti C/Si, Ti/Al/C and Ti/Ti C/Al with different volume concentration of abrasive respectively. Then, the phase composition and microstructure of prepared composite are analyzed by X-ray diffraction（XRD）, scanning electron microscope（SEM） and energy-dispersive spectroscopy（EDS）.The results indicated that Ti and C powder as titanium and carbon source, which is more favorable to synthesis of the ternary phase materials. In 3Ti-Si-2C-based superhard composites, for the synthesize of Ti₃ Si C2, excessive Si is useless, however, adding a small amount of Al is more favorable.In 3Ti-Al-2C-based superhard composites, it’s better to the synthesize of Ti₃ Si C2,and the development of crystal by increasing Al content. Abrasive takes part in the reaction system, which have obtained the chemical bonding between abrasive and binder. The influence of the abrasive to the reaction system depends on the synthesis of ternary phase. The reaction is completer, the abrasive has the littler influence on the synthesize of Ti₃ Si C2 and Ti₃ Al C2. Or conversely on the contrary.The reaction mechanism of Ti₃ Si C2 and Ti₃ Al C2, and the interface reaction mechanism of abrasive with binder have been studied according to the analysis of thermodynamics and DSC/TG. The synthesis of Ti₃ Si C2 and Ti₃ Al C2 were both solid-liquid reactions. The highly exothermic reaction between raw materials were triggered by heating up, to synthesize Ti-Si/Ti-Al compounds and Ti C as the intermediate products. Then, at high temperature, ternary phase could be synthesized by reaction of the molten Ti-Si/Ti-Al compounds with generated or original solid-phase Ti C. Diamond could be directed involved into the reaction system. C on the surface of diamond reacteds with Ti and formed Ti C firstly, then Ti C reacted with molten Ti-Si compound and formed Ti₃ Si C2 on the surface of diamond. CBN reacted with Ti, Al, to form the transition layer of borides, nitrides between CBN and binder.Through the hardness test and grinding test of composite materials, the results indicated that the hardness of material was improved with the increasing of the ternary phase-content of composite. And the binder itself with superior grinding performance was combined with abrasive well, which could be applicable to grind.Through the analysis of the surface topography of diamond by SEM, and the test of single diamond compressive strength, showed that the Single diamond compressive strength droped due to chemical corrosion on the surface of diamond. However, diamond was hardly bound to suffer thermal damage and graphitization, which had little impact on the whole mechanical property of composite.