Synthesis and sintering of ZrB2-SiC based composites have been carried out in a single-step pressureless reaction sintering (PLRS) of ZrO2, B4C, and Si. Y2O3 and Al2O3 were used as sintering additives. The effect of ratios of ZrO2/B4C, ZrO2/Si, and sintering additives (Y2O3 and Al2O3), was studied by sintering at different temperatures between 1500 and 1680 ℃ in argon atmosphere. ZrB2, SiC, and YAG phases were identified in the sintered compacts. Density as high as 4.2 g/cm3, micro hardness of 12.7 GPa, and flexural strength of 117.6 MPa were obtained for PLRS composites. Filler material was also prepared by PLRS for tungsten inert gas (TIG) welding of the ZrB2-SiC based composites. The shear strength of the weld was 63.5 MPa. The PLRS ZrB2-SiC composites exhibited: (i) resistance to oxidation and thermal shock upon exposure to plasma flame at 2700 ℃ for 600 s, (ii) thermal protection for Cf-SiC composites upon exposure to oxy-propane flame at 2300 ℃ for 600 s.
- Article type
ZrB2 and ZrB2-SiC powders have been produced by reducing ZrO2 and ZrSiO4 with B4C without using any furnace. Magnesium was added to the mixtures of (ZrO2+B4C) and (ZrSiO4+B4C). The reaction has been assisted by a floral thermite packed around the compacts. By introducing elemental Si into (ZrO2+B4C) mixture, composite powders of ZrB2-SiC formed. After leaching out MgO with suitable HCl water solution, the product was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of Si, B4C, and Mg on the extent of formation of ZrB2, ZrB2-SiC, and other phases has been studied. Formation of nano-sized ZrB2 and ZrB2-SiC composite powders was identified. The adaptability of the process for bulk production was examined.