Fabrication of Bulk Nanocrystalline Ceramic Materials

An alternative method to produce bulk nanocrystalline materials is to produce amorphous material by rapid solidification followed by controlled solid state crystallization. Four different materials studied in this work are based on near-eutectic mixtures of alumina, zirconia, and silica. Powder feedstock materials have been plasma sprayed using a water stabilized plasma torch (WSP®) and subsequently heat-treated to prepare materials with nanocrystallites of 12 nm diameter on average. The as-sprayed materials have very low porosity and are mostly amorphous. The as-sprayed amorphous materials crystallize at temperatures around 950 °C. The resulting structure is best described as nanocomposite with the very small crystallites embedded in an amorphous matrix. The role of silica on phase composition, microstructure, and mechanical properties of the as-sprayed and annealed materials is discussed. The as-sprayed amorphous materials exhibit high hardness and high abrasion resistance. Both properties are significantly improved in the heat-treated nanocrystalline samples.