Abstract
Nitrogen rich multication α-SiAlON ceramics doped with Y-Ce have been densified by gas pressure sintering using α-Si3N4 or mixed β/α-Si3N4 starting powder. The effects of α-SiAlON nucleation and growth mechanisms were investigated by using di fferent sintering cycles. X-ray diffraction studies after sintering revealed that 21R polytype phase was present in addition to α -SiAlON matrix phase. Microstructural characterisation of sintered materials prepared using α-Si3N4 powder in the starting composition revealed a typical equiaxed grain morphology, as expected if the α-SiAlON nucleation step was not applied before grain growth. However, needlelike α-SiAlON grains were observed if a nucleation step was carried out before final sintering. In starting powders containing mixed β/α-Si3N4, needlelike grain morphology was also observed. The effects of different Si3N4 starting powders and sintering conditions on the grain morphology and mechanical properties are discussed.