What is it about?
This paper reviews investigations of silicon nitride–silicon carbide micro– nanocomposites from the original work of Niihara, who proposed the concept of structural ceramic nanocomposites, to more recent work on strength and creep resistance of these unique materials. Various different raw materials are described that lead to the formation of nanosized SiC within the Si3N4 grains (intragranular) and at grain boundaries (intergranular). The latter exert a pinning effect on the amorphous grain boundary phases in the silicon nitride and also act as nucleation sites for β-Si3N4, which limits grain growth during sintering. This finer microstructure results in strengths higher than for the monolithic silicon nitride. Intragranular SiC particles enhance strength and fracture toughness as a result of residual compressive thermal stresses within the nanocomposites. High temperature strength and creep resistance are also much higher than for monolithic silicon nitride and a few investigations of these topics are briefly reviewed and the proposed mechanisms are described. Within the context of other studies cited, work on Si3N4–SiC micro–nanocomposites by the current authors describes an aqueous processing route for better dispersion of commercial powders prior to sintering.
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Perspectives
In summary, excellent properties at ambient and elevated temperatures have been reported for Si3N4–SiC nanocomposites produced from a range of precursor materials some of which are very expensive. So far, most investigations have processed powders using mixing in ethanol followed be evaporation, which is not ideal for scaling up the manufacturing process. The present authors have addressed some of these points and have produced Si3N4–SiC nanocomposites using commercially available powders and following established techniques for dispersion of nanosized SiC inclusions using aqueous processing. Many of the studies cited have produced dense nanocomposites by hot pressing, which is not suitable for large-scale production. The crucial factors that govern the development of materials with the desired properties, such as powdered raw materials, dispersion in water, drying, shaping, and choice of sintering technique, need to be considered and well understood. This will require further basic researchinto the processing–micro/nano/structure–property relationships in these Si3N4–SiC micro–nanocomposites with a view to identifying suitable applications that will benefit from their unique characteristics.
Professor Stuart Hampshire
University of Limerick
Read the Original
This page is a summary of: Silicon nitride–silicon carbide micro/nanocomposites: A review, International Journal of Applied Ceramic Technology, September 2021, Wiley,
DOI: 10.1111/ijac.13903.
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