4 - Al2O3-SiC nanocomposites: Preparation, microstructure, and properties

Abstract

Wider commercial utilization of SiC-containing alumina nanocomposites is limited due to lack of cheap and reliable way of preparing dense, defect-free ceramics with complex shape and with homogeneously distributed SiC nano-particles. The most promising among unconventional processing routes is so-called “hybrid” route, utilizing ceramization of organosilicon polymeric precursors, typically a polycarbosilane, as the source of SiC. It comprises coating of alumina particles or infiltration of presintered alumina matrix with dissolved polymer, drying, cross-linking and pyrolysis of the polymer, and final densification. The SiC particles are formed in situ, inside the alumina matrix. This way their homogeneous distribution is ensured. The composites are of typical interintra type, with SiC particles located both inside the alumina matrix grains (spherical particles with radius ranging from 10 to 200nm) and at alumina–alumina grain boundaries. The latter are often present in the form of whiskers with the length ranging from 100 to 500nm. Nanocomposites with high fraction of SiC (up to 21vol%) and with unique microstructure consisting of submicron alumina matrix (mean size of alumina grains 0.9μm) and homogeneously distributed spherical SiC inclusions can be also prepared. All studied materials exhibit high hardness and excellent resistance against abrasive wear. The composites prepared with the use of organosilicon polymer as a source of SiC are compared to those prepared by a conventional mixing of submicron alumina and SiC powders.