Development In-Situ Platelet Reinforced Alumina

Abstract

It has been shown that alumina is a strong ceramic material, but it typically exhibits poor fracture toughness. Recently, studies have found that liquid-phase sintered alumina containing an invert glass (i.e., high calcium with low silica) can precipitate what appear to be high-aspect ratio needle-like crystals that have been determined to be calcium hexaluminate (CaO·6Al2O3, CA6). In this study, the chemistry and processing conditions used to create the first specimens were revisited and it was determined how the sintering conditions contributed to densification of the alumina matrix and the size and population of the CA6 precipitates. While keeping the ratio of CaO:SiO2 constant, it was observed that the number of CA6 precipitates appeared to increase in number and size with increased CaO and SiO2 level (that is, with more liquid phase). In addition, it appears that the precipitates are nont needles, but platelets. The sintering conditions had little contribution to the size and concentration of the precipitates but were found to aid in the densification of the alumina matrix. The ability to control the size and concentration of these grains may have the potential to affect the fracture toughness of alumina, but this is beyond the scope of this work.