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FABRICATION OF HIGHLY DENSE PURE 6H-SiC CERAMICS VIA THE PVT METHOD USING SUB-MICRON SiC POWDERS

The dense SiC ceramics were prepared by the physical vapour transport (PVT) method using three types of SiC powder with different grain size, including a kind of SiC powder with a mean diameter of 500 nm. The effects of the grain size of the raw materials on the bulk density, bending strength and hardness of the SiC ceramics were studied. It was found that with a decreasing grain size, the bulk density and the bending strength of the fabricated SiC ceramics increased, while the Vickers hardness decreased. the effects of the grain size of the raw materials on the nucleation density and the growth rate of the SiC were analysed, and the growth characteristic of the SiC ceramics was systematically explored. The results indicated that the crystal type, the nucleation density and the growth rate were obviously affected by the soaking temperature. When the temperature was higher or lower than 2200 °C, the fabricated ceramics was composed of a 6H–SiC polycrystalline or the mixture of a 6H–SiC and 3C–SiC polycrystalline. Meanwhile, with an increasing temperature, the nucleation density decreased and the growth rate increased. Obviously, by optimising the fabrication process, highly dense 6H–SiC ceramics with a bulk density of 3.07 g∙cm and a bending strength of 335.6 ± 10 MPa could be rapidly fabricated by the PVT method using the sub-micron SiC powder.