Pressureless sintering of AlN-SiC composites

SiC-AlN composites have been successfully pressureless sintered by using commercial SiC and AlN powders with the optimum amount of sintering aid. The important parameters during pressureless sintering, including the amount and type of sintering aids, sintering temperature, sintering period and packing powder have been studied. Yttria was found to be a better sintering aid than alumina or calcia. The yttria sintering aid reacts with AlN and SiC powders and forms a Y-Al-Si-O-N grain-boundary phase to assist densification during pressureless sintering. With 2 wt% yttria, SiC-AlN composites can be pressureless sintered to high density at 2050–2100 °C for 2 h under the firing conditions where alpha-pp packing powder is used during firing. The microstructure and phases of the composites were characterized by using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffractometry.