Preparation Of TiB₂-SiC Nanocomposites By Chemical Precursors

Titanium diboride (TiB2) is a new engineering ceramic material, with excellent temperature resistance, high hardness, high modulus and low specific gravity, also has an excellent thermal shock resistance, so it becomes a new key material of national defense as its excellent performance. But the brittle, difficult process, and poor thermal shock resistance of TiB2 limits its application in future, so how to improve the strength and toughness of TiB2 is one of the key issues at present. And now, most of people take the techniques that refine the grain and the second-phase dispersion strengthening to improve the strength and toughness of TiB2, but it is difficult to refine the grain of TiB2, while the sintering conditions can be quite harsh, so refine the grain of TiB2 is in little progress, and most study focused on the technique of second-phase dispersion strengthening.In this thesis, TiB2/SiC nano-composite were prepared by the in situ synthesis of precursor, and the nano SiC that prepared from precursor were studied detailed. The TiB2/SiC composite were sintered by hot press sintering (HP) and spark plasma sintering (SPS), its characterization were studied to research the relationship between structure and properties.First, the nano SiC that prepared from precursor were studied. The morphology of nano-SiC were controlled by control the heating rate during pyrolysis, and the thermal stability of nano-SiC was studied. Well dispersed nano-SiC were obtained by refine the precursor using the equipment of MICROS. It could be found that:well dispersed nano SiC could be prepared by using the pyrolysis of precursor.TiB2/SiC composite could be get by using the in situ synthesis of precursors, it could be found that the pyrolysis products of precursor played a binder role in the composite to bond the TiB2 particles together. The components within the system and the pyrolysis products were mutually stable, they didn't react with each other, and they also didn't undermine the structure between each other when the composite were in high temperature. For the SiC, the higher the temperature the better crystallization. The prepared composite was sintered by HP sintering, the structure of sintered body was uniform and compact, there was no grain growth abnormal and no impurities in sintered body after sintering. The phases in composite were stability with each other, and the crystallized SiC grains existed between TiB2 to formed the structure of nanocomposite.TiB2/SiC composite were prepared by using the refined TiB2 and precursor. Refined powder had smaller particle size, large specific surface area, and their surface activity became better which it is conducive to the binding between the components of composite. The composite after pyrolysis was refined by the planetary ball mill to disrupt the reunite of composite which was conducive to sintering. The refined composite was sintered by SPS. It could be found that:the structure of the sintered TiB2/SiC composite by SPS was uniform and compact, the grain were small.