Abstract: The microstructures of Ln-α-Sialon-AlN-polytypoid(Ln=Y, Y+Sm and Sm)dual-phase ceramics, with a overall composition 90wt%α-Sialon(m=1, n=1.7)+10wt%12H,
hot-pressed in the range of 1650～1800℃, were studied by SEM. The results show that in all compositions, α-Sialon grains are small at 1650℃ and part of them exhibits elongated morphology at 1800℃.
The morphologies of α-Sialon grains are slightly varied with different rare-earth elements. Sm-α-Sialon exhibites the finest microstructures
with the aspect ratio of elongated grains of 7～9. In Y-composition, α-Sialon is coarsest grains with the aspect ratio of elongated grains of 2～3. There is
agglomerated AlN-polytypoid in all compositions, and which shows fiber-like morphology. The extent of non-uniform distribution of AlN-polytypoids in these
composite ceramics decreases in the sequence of Y-, Y+Sm- and Sm-composition. These differences of microstructure may be attributed to the effect of different
rare-earth elements on the formation kinetics of Ln-α-Sialon-AlN-polytypoid dual-phase ceramics.

Key words: rare-earth elements, Ln-α-Sialon-AlN-polytypoid dual-phase ceramics, microstructures