Kansei Izaki

Hot-pressed Si3N4-32% SiC nanocomposite from amorphous Si-C-N powder with improved strength above 1200 °C

On montre que la resistance a la rupture du manocomposite Si 3 N 4 - 32% SiC est amelioree de facon significative si on remplace Y 2 O 3 /Al 2 O 3 par Y 2 O 3 seul comme additif de frittage

Microstructure and thermal conductivity of Si3N4SiC nanocomposites fabricated from amorphous SiCN precursor powders

Abstract Thermal conductivity of Si 3 N 4 SiC nanocomposites, in which nanosized SiC particulates were dispersed within the matrix grains and/or at the grain boundaries, was evaluated at the temperature range of 293 to 1273 K. The composites were prepared by hotpressing amorphous Si-C-N precursor powders. The thermal conductivity of the composites decreased slightly with the SiC addition up to about 20 vol.% SiC and then increased, which is markedly different from what was expected from the rule of mixture. This singular behavior of thermal conductivity was attributed to the peculiar microstructure of Si 3 N 4 SiC nanocomposites.

Intragranular crack deflection and crystallographic slip in Si3N4/SiC nano-composites

Abstract Crack deflection is a potential mechanism for toughening essentially brittle materials. Deflection generally occurs along grain boundaries and is enhanced by particles with high aspect ratios. Si 3 N 4 /SiC ceramic/ceramic composites contain elongated β Si 3 N 4 grains as a major phase and provide a good illustration for this mechanism. As a result, such materials demonstrate a relatively good fracture toughness. It is shown in this study, using transmission electron microscopy (TEM), that transgranular cracks, which develop at low temperatures and/or high deformation rates (present case), may also be deflected by intragranular SiC inclusions. Cracks use the 100 planes and propagate along the 〈100〉 directions of the silicon nitride hexagonal lattice. Further, after large plastic deformations at high temperature, slip defects are observed in silicon nitride grains, with many step-like deviations (‘cross’ slip), and the slip system is found to be [001] {100}.

The Correlation Between Interface Structure and Mechanical Properties for Silicon Nitride Based Nanocomposites

Si3N4/SiC nanocomposites were prepared by hot-pressing fine, amorphous Si-C-N precursor powders. Transmission electron microscopic observation revealed that the nano-sized SiC particles are dispersed within the matrix grains and/or at the grain boundaries, depending on the volume fraction of the SiC, the size of the SiC particles, and the sintering conditions. The intragranular nano-sized SiC particles affect the growth of elongated Si3N4 grains thereby improving fracture toughness and strength. The intergranular nano—sized SiC particles act to control the grain boundary structure by connecting directly with the matrix Si3N4 grains without the interface layer, thereby improving the high-temperature fracture behavior.

Preparation of fine silicon nitride powders by vapor phase reaction of nitrogen containing organosilicon compound with ammonia

Fine amorphous silicon nitride powders were prepared by vapor phase reaction between nitrogen-containing, chloride-free organosilicon compound and NH3 at the production rate of-200g/h. Crystallization was carried out by heat treating the resulting amorphous powders in Ar atmosphere at 1500°C. High purity crystalline silicon nitride powders could be synthesized with metallic impurities Fe, Al, Ca 95wt%, respectively. Mechanical properties of hot-pressed silicon nitride from the resulting crystalline powders were comparable to hot-pressed bodies fabricated from high purity silicon nitride powders by imide decomposition and carbothermic reduction of silica.