Properties Of SiC/nano-TiN Composite Slurry And Preparation Of Multiphase Ceramics

Silicon carbide (SiC) ceramics is a kind of structural materials with excellect properties such as high strength, high hardness, resistance to extreme temperature, corrosion and abrasion, and excellect mechanical and thermal properties in high temperature. However, the low toughness and worse reliability of SiC ceramics leads to a high waster rate of products during the production process, which limits its application in wider range of areas. TiN has the similar mechanical and thermal properties with SiC. By introducing the TiN nanoparticles into the SiC matrix, the brittle shortcoming of SiC ceramics could be improved with the strengthening and toughening mechanisms of nanoparticles, and then SiC/nano-TiN multiphase ceramics with high strength and toughness could be prepared.Based on the present research of SiC and nanocomposite ceramics, the composition of SiC/nano-TiN multiphase ceramics was designed, the dispersion behavior of nano-TiN and SiC in the aqueous medium was investigated, and the best dispersion conditions were found out. By investigating the effect of dispersant content, solid loadings and nano-TiN content on the rheological properties of the SiC/nano-TiN slurry, the slurry which meets the requirement of the spray drying was prepared, and the SiC/nano-TiN composite powders with favorable dispersibility of nanoparticles, even distribution of ingredients and good molding performance were prepared by spray drying. With pressureless liquid phase sintering, the SiC/nano-TiN multiphase ceramics with excellect properties were prepared by adjusting sintering temperature, holding time and the content of nano-TiN, which provides the basis of composite ceramic products for the industrial production and expands the application of SiC. The following is the main tasks:(1) Dispersion properties of nano-TiN and SiC in the aqueous mediumWith the increasing of pH value, the surface potential of nano-TiN and SiC changed from positive to negative, and the good dispersibility and stability were obtained when pH value was equal to or more than 8. TMAH could be adsorbed onto the surface of nano-TiN and SiC. The best result was obtained when the content of TMAH was 0.75wt%. The particle size distribution of nano-TiN was a single peak and the median diameter was 89.9nm, and the relative sedimentation height of SiC suspension remained over 99% after 7 hours when the pH value was 8 and the content of TMAH was 0.75wt%.(2) Rheological properties of the SiC/nano-TiN slurry and preparation of composite powdersWith the increase of TMAH content, the viscosity and shear stress of SiC/nano-TiN slurry decreased. The viscosity of the slurry was 9mPa·s and the shear stress was less than 4Pa when the TMAH content was 0.75wt%. With the increase of solid loading, the viscosity and shear stress of SiC/nano-TiN slurry increased, and the 40wt% solid loading slurry was more suitable for spray drying. The rheological properties of the slurry were affected seriously by the content of nano-TiN. The viscosity and shear stress were low at the whole range of the shear rate when the content of nano-TiN was 5wt%. With the increase of nano-TiN content, the viscosity and shear stress increased quickly. The SiC/nano-TiN composite powders with favorable dispersibility of nanoparticles, even distribution of ingredients and good molding performance could be prepared by spray drying.(3) Preparation of SiC/nano-TiN multiphase ceramicsThe contractiveness and weight loss of SiC/nano-TiN multiphase ceramics increased with the increase of sintering temperature and holding time, and decreased with the increase of nano-TiN content. With the increase of sintering temperature and holding time, the SiC and nano-TiN grain grew up, but Nano-TiN particles could refine the SiC grain. Phase analysis and thermodynamic calculation indicated that TiN could react with matrix to produce TiC. The relative density was 98%, bending strength was 686.8MPa, fracture toughness was 7.04MPa·m^1/2 and hardness was 21.73GPa when the multiphase ceramics added 5wt% nano-TiN and sintered at 1850°C for 1 hour. The strength was enhanced as the SiC boundaries were pinned and strengthened by nano-TiN particles, and the toughness was enhanced by the residual stress and crack bridging.