??? Transformation in sialon ceramics

Abstract

A number of different starting compositions, within or just outside the ?-sialon stability region of yttrium sialon system, were prepared using the oxides of rare-earth elements (Nd, Sm, Dy and Yb) as ?-sialon stabilizers. The powder mixtures were densified by pressureless sintering. The resulting materials were heat treated at 1450°C for up to720 hours (1 month) to observe ???-sialon transformation. It has been observed that stable ?-sialon materials can be prapared from all rare-earth elements regardless of their ionic radii. The microstructural analysis of heat treated samples has revealed that the main reason for the transformation from ?-sialon to ?-sialon is the presence ?-sialon grains in as-sintered samples, which acted as nucleation sites for the transformation at heat treatment temperatures. It has also been observed that ???- sialon transformation increases as the ionic radii of rare-earth elements increase in the order Yb?Dy?Sm?Nd.