Abstract: Based on the phase relationships in the Dy-Si-Al-O-N system, α-Sialon ceramics and α-β-Sialon composite ceramics with garnet and/or melilite as grain boundary phases were designed. The densification behavior, α’→β’ phase transformation in heat-treatment, mechanical properties and microstructure characteristic were studied. The results show that Dy-α’ and Dy-α’-β’ ceramics with garnet and/or M’ as grain boundary phases can be fabricated by HP. DyAG as an additive is more effective than M’ in promoting densification. Dy-α’ is kinetically more favourable to be formed over the other Dy-containing phases unlike the other Ln-α-Sialons, thereby the fractions of the α’ phase in the as sintered specimens is higher than the designed ones. By post sintering heat-treatment, the α’→β’ phase transformation occurs and the designed
α’/α’+β’ ratios can then be achieved.

Key words: Dy, Sialon, fabrication, phase transformation