SiAlON Composites Containing Rare-Earth Melilite and Neighboring Phases

• Published in: Journal of the American Ceramic Society 1996-08, Vol.79 (8), p.2081-2090
• Main Authors: Huang, Zhen-Kun, Liu, Shih-Yu, Rosenflanz, Anatoly, Chen, I-Wei
• Format: Article
• Language: English
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Structural ceramics; Technical ceramics
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1996.tb08940.x

Sintering aids with a formulation of rare‐earth (R) melilite solid solution M'(R) have been introduced to several SiAlON composites to obtain high‐density bodies by pressureless and gas‐pressure sintering. These compositions include ones along the Si3N4–R2O3:9AlN line, which contain no Al2O3 and are known to have excellent strength but very poor sinterability. Phase analysis and property (hardness, toughness, strength, and oxidation resistance) measurements reveal a complex set of structure–property–processing relationships that are composition‐dependent. Of the most importance is the Al—O content in various phases, which is dictated by the starting composition as well as Al—O solubility in M'(R). This influences the sinterability, strength, and phase assemblage through the compositions of the intermediate liquid and the final β'‐SiAlON. La2O3 is further established as an effective sintering aid that does not affect the equilibrium phase assemblage. Overall, M'(R) and La2O3 show promise as SiAlON sintering aids that allow high density to be achieved without compromising intrinsic mechanical and thermal properties.