Preparation Of Silicon Carbide Multiphase Ceramics And Analysis On Microstructure And Properties

Reaction bonded silicon carbide ceramic materials has many excellent performance, such as high-temperature oxidation resistance, corrosion resistance, resistance to wear and tear, heat shock resistance, which make it become one of the most effective methods of silicon carbide preparation.In the present thesis, the sub-micron silicon carbide powder was used the main starting material, and through appending the different content of nano-SiC and graphite, was used to prepare silicon carbide ceramics by using vacuum sintering processes at 1500℃. The microstructure, density, apparent porosity, room temperature mechanics and oxidation resistance of silicon carbide ceramic had been systematically analyzed through XRD, SEM techniques as well as Archimedes law, three-point bending, single edge notched beam bending and Vicker's hardness indentation methods.Experimental results showed that when the content of graphite is 22.22 wt%, the variation of density of specimen is caused by filling of particles mainly. When the content of graphite is 17.77 wt%, the variation of density of specimen is caused by the great friction force caused during molding.After analyzing the hardness of silicon carbide prepared through the four different schemes, it could be found that the hardness of silicon carbide ceramics decreased with the increasing of content of free silicon and homogeneousness.The hardness of silicon carbide ceramics prepared through scheme 3 reached peak (HRA=65.4). When the content of free silicon was 22.4 vol%, flexural strength and fracture toughness reached the maximum values, 386 MPa and 4.19 MPa·m1/2 respectively. In accordance with the four schemes prepared ceramics, the cuts which taken on combining features of intragranular and intergranular. After analyzing the surface indentation of specimen prepared through scheme 3 and scheme 4, it was found that the cracks were more tortuous. Therefore, it was considered that the toughening mechanism was the cracks deflection.The oxidation of SiC prepared by reaction sintering was processed in still air for 60 h at 1100℃. Experimental results showed that the oxidation kinetics...