THE FLUORINE EFFECT ON THE GRAIN-GROWTH OF $\alpha^1$:$\beta^1$-SiAlON CERAMICS

Abstract

SiAlON ceramics are of major interest for industrial applications due to their excellent mechanical properties. The starting Si3N4 powder (? or ?), the type of sintering additive and sintering conditions govern the microstructural evolution of SiAlON ceramics. In this study, ?ı:?ı SiAlON ceramics with an equal mole intergranular phase content, different type cation systems (Y:Sm:Ca and Ca:Ce) with different molar ratio (30:64:6 and 33:67) were produced by using coarse (d50=1 µm) ?-Si3N4powder. CaF2 and CaCO3 were utilized as Ca sources. Despite the fact that ?ı-SiAlON phase cannot be stabilized in Ca:Ce (CaCO as a Ca source) system, ?1-SiAlON phase stability and unpredictable ?1-SiAlON grain-growth in both a and c directions was achieved when CaF2 was incorporated in the composition. On the other hand, an increase in ?-SiAlON amount and more elongated SiAlON grain evolution was observed when CaF2 was used instead of CaCO3 in Y:Sm:Ca cation system. Furthermore, using CaF2 instead of CaCO3 gave rise to an increase in densities. Therefore, the substantial effect of CaFon abnormal grain growth and ?ı-SiAlON phase stabilization was observed.