Microstructures of Ln-α-Sialon-AlN-Polytypoid (Ln=Y, Y+Sm and Sm)Dual-phase Ceramics

The microstructures of Ln-α-Sialon-AlN-polytypoid(Ln=Y, Y+Sm and Sm)dualphase 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 aJspect 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 cerarnics.