The role of boron and carbon additions on the microstructural development of pressureless sintered silicon carbide

Abstract The role of boron (B) and carbon (C) additions on the microstructural development of pressureless sintered silicon carbide (SiC) was examined. Green compacts, which have been fired at a rate of 20 K/min up to 1773, 2123, 2223 and 2423 K were analyzed by means of electron microscopy and high-resolution scanning Auger electron spectroscopy. In the first stage of sintering C forms a uniform layer on the SiC grains. B and O are also present in that layer. At higher temperatures C reacts with SiO 2 under formation of SiC. B disappears from the layer of C as well as from the grain boundaries. The final dense material exhibits SiC crystallites and polycrystalline C-inclusions. The results are discussed under microstructural aspects and with respect to the sintering process of SiC.