Abstract
The microstructure and physical properties of new Y2O3 and Al2O3 oxide-doped silicon nitride ceramics fabricated by cold isostatic pressing and free sintering were investigated. The phase composition of produced material was also studied by X-ray diffraction at room and elevated temperature. The fabricated ceramics featured a microstructure of Si5AlON7 grains with a fine-grained α-Si3N4 with a small amount of Y2SiAlON5. Described ceramics is attractive for many high-temperature structural applications due to beneficial combination of fine-grained structure with improved mechanical properties and small weight loss.
Highlights
Silicon nitride is one of the most promising structural materials for high-temperature applications because of its excellent strength and toughness at elevated temperatures, good thermal shock resistance, low coefficient of thermal expansion, and chemical stability [1,2,3]
We have developed a novel process involving cold isostatic pressing (CIP) and pressureless sintering in a nitrogen atmosphere
It was reported that the materials having microstructure with the finest and coarsest elongated β-grains showed the high value of fracture toughness, whereas materials with the microstructure with the mixture of elongated thin and thick β-grains had lower facture toughness [13]
Summary
Silicon nitride is one of the most promising structural materials for high-temperature applications because of its excellent strength and toughness at elevated temperatures, good thermal shock resistance, low coefficient of thermal expansion, and chemical stability [1,2,3]. Its densification is rather difficult by classical sintering process due to the strongly covalent in Si–N bonds which results in low self diffusivity [4] Such oxide additives as MgO, Al2O3, Y2O3, and Al2O3 + Y2O3 combination are considered as the most commonly used and ideal additives for Si3N4 ceramics due to their high melting point and because of the possibility to control the α→β phase transformation rates of the Si3N4, the aspect ratio of the β-Si3N4, and the grain growth anisotropy. These additives lead to high mechanical properties at room temperature as well as at elevated temperatures [3]. The use of rare-earth oxide additives to provide a liquid phase for sintering is required for obtaining
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