Sintering of a - sic at high pressures and temperatures

The high temperature properties of sintered silicon carbide are critically dependent on additives which are used for consolidation by conventional hot pressing into pore-free bodies. The sintering aids provide increase in shrink-age rate and high densities at low sintering temperatures. However, the presence of sintering aids results in a second phase at the grain boundaries which13; has adverse effects on the high temperature properties. An effort has been made to produce fully dense self bonded Sic without using sintering aids by high pressure-high temperature sintering. The Sic powder has been sintered13; at pressures (1.7-3.0 GPa) at 18OO0C for 5-30 minutes. The densities 'of the sintered compacts are gt; 99% theoretical density. The compacts show room temperature hardness values in the range 26.7-33.5 GPa. The indentation frac-13; ture toughness values range between 3.5 and 3.9 MPaJ;;E. The microstructural studies have shown that pressure plays an important role in the densification and bonding of silicon carbide