Effect of starting Si3N4 powder type and sintering conditions on the grain morphology of ?-SiAlON ceramics

Abstract

Nitrogen rich neodymium-ytterbium containing multi-cation ?-sialon starting compositions have been prepared by gas pressure sintering using "conventional" ?-Si3N4 or plasma produced ß-Si3N4 powder. The effect of ?-SiAlON nucleation on growth mechanism was investigated by applying different sintering cycles. X-ray diffraction studies of these compositions after sintering revealed that ?-sialon was observed as a matrix phase. Microstructural characterisation of the sintered materials by using ?-Si3N4 powder as starting composition resulted in a typical equiaxed grain morphology, as expected if the ?-SiAlON nucleation step is missed out prior to growth. However, elongated ?-SiAlON grains were observed by applying nucleation. In the case of ß-Si3N4 containing starting composition, in all cases ?-SiAlON grain morphology was observed. The effects of starting Si3N4 powders and different sintering conditions were discussed in detail.