Hot-Pressed ceramics of ultradisperse composite powders

Abstract

The regularities of variation of the microstructure, phase composition, degree of crystallinity, and properties of hot-pressed ceramics prepared from ultradisperse composite powders of the Si3N4 - Y2O3 system depending on the β/α phase ratio in Si3N4 and the concentration of Y2O3 are discussed. An increase in the concentration of Y2O3 in composite powders up to 15 – 18% and a decrease in the β/α ratio of Si3N4 lead to a change of the composition of the secondary crystalline phases with an increase in their refractoriness (from silicon oxynitride and yttrium silicates to complex yttrium — silicon oxynitrides), a lower concentration of the vitreous phase, a higher degree of crystallinity, and a higher content of stretched grains in the structure of the ceramics. The presence of the high-melting phase of yttrium — silicon oxynitrides improves the phase and granular homogeneity of the structure that forms by the type of solid solutions, with an essentially similar composition of the grains and the intergranular phase. The formation of a high-melting fine-grained self-toughening structure with a coefficient of grain elongation up to 8 – 9 ensures a high and practically stable level of the mechanical properties of the synthesized materials at temperatures up to 1400 – 1500°C.