The Fluorine Effect on the Grain-Growth of -SiAlON Ceramics

Abstract

SiAlON ceramics are of major interest for industrial applications due to their excellent mechanical properties. The starting Si 3 N 4 powder (α or β), the type of sintering additive and sintering conditions govern the microstructural evolution of SiAlON ceramics. In this study, α ı :β 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 (d 50 =1 µm) β-Si 3 N 4 powder. CaF 2 and CaCO 3 were utilized as Ca sources. An increase in α ı -SiAlON amount in the case of employing CaF 2 as opposed to CaCO 3 in Y:Sm:Ca cation system was observed. Despite the fact that α ı -SiAlON phase cannot be stabilized in Ca:Ce (CaCO 3 as a Ca source) system, α ı -SiAlON phase stability and unpredictable α ı -SiAlON grain-growth in both a and c directions was easily achieved when use of CaF 2 . Furthermore, using CaF 2 instead of CaCO 3 gives rise to an increase in densities. Therefore, the impressive effect of CaF 2 on abnormal grain growth and α ı -SiAlON phase stabilization was discussed.