Theoretical hardness analysis and experimental verification for SiAlON based nano-composites

Abstract

SiAlON is a commercially important family of ceramics. These are based upon silicon nitride and inherit much of the useful properties like high fracture toughness and high hot hardness making it useful for harsh environments like automobile and gas turbine engines. Extensive research has been done on SiAlON to determine the effects of type of additives, composition of precursors, size of precursor particles, sintering techniques, heating and cooling rates etc. on SiAlON microstructure, phases and properties. SiAlON is continuously being made better by innovating and optimizing the above mentioned techniques and properties. A further step in the evolution of advance ceramics are SiAlON composites, in which different materials are used as a reinforcement in a SiAlON matrix to further enhance its properties. This area of research presents its own challenges like achieving complete densification even for high second phase content, preventing undesired phase transformations of second phase particles, achieving elongated grains of SiAlON in a composite etc. This review paper will attempt to comprehensively cover the latest techniques being utilized to improve the properties of SiAlON and then discuss the formation of promising SiAlON composites, their limitations and promising future work to make better SiAlON composites. This review paper will also calculate theoretical hardness of nanocomposites under study, relate their theoretically calculated and experimentally obtained values, and attempt at explaining the causes for the differences in these values.