.alpha.'-Sialon ceramics: a review

a' -Sialon ceramics promise the possibility of a reduction of the amount of glassy grain boundary phases by incorporating the oxides, present in the starting mixture as either sintering additives or impurities, into its rmallattice. It has been shown that techniques such as gas pressure sintering can be used successfully to obtain fully reacted and dense a'- or (a' + ß')-sialons. By combination of suitable modifier cations and heat treatment the amount of grain boundary phases can be kept very low. This may lead to improved mechanical properties, especially at elevated temperatures. The equiaxed microstructure of a' -sialons, compared with the needlelike structure of ß'sialons, leads to specific differences in mechanical behavior. However, at this moment the complicated interrelationships between the formation sequence, fabrication conditions, properties, and microstructures are still insufficiently understood. Yet, even with the resent-day materials, wear resistance, high-temperature mechanical strength, thermal shock resistance, and oxidation resistance are such that further studies are worth-while.