Research on Preparation and Mechanical Properties of Fine-crystalline Si_3N_4/Al_2O_3 Composite Ceramic

Abstract: SisN'-based composite ceramics have attracted attention owing to itsoutstanding physical, mechanical properties and high wear-resistance, gooderosion-resistance. But the fatal brittleness still exists in these materials, and themechanical reliability is also low. The fine crystalline ceramics was researchedpopularly at present. In this thesis, the fine-crystalline Si3N4/Al2O3 compositeceramics were prepared by hot pressing. The phenomena including the properties ofpowder, sintering process, densification and mechanical properties were discussedby the experimented research and theoretical analysis. The experimenta1 andtheoreticaI basis has been presented for further research.First, the research on the properties of powders was done. The resultsrevealed that the formation of agglomerates and the absorbed oxygen affected thesintering process and mechanical properties of these fine-crystalline materials.When the powders have been heat-treated at 1200C, the fine crystalline materia1shave been obtained due to the phase transformation and thermal inactivation.Second, the research on the effect of the sintering temperature and theprotective gas on the densification and the mechanical properties of these materialswas worked on. The higher the sintering temperature, the higher the density. thebetter bend strength and hardness. but the variation of fracture toughness propertiesdepended on the kind of addition. When the protective gas was N2, the oxidationand the decomposition have been pressed. But when Ar was used, the seriousoxidation has been happened.Third, the research on the effect of the kind of addition on the densificationand the mechanical properties of these materials was conducted. Under the sametemperature, with the increase of the sort of the additions, the density and themechanical properties of these materials have increased. But a proper proportion ofnitrogen in the addition should been defined, otherwise, a contrary result has beenrec eived.Last, the research on the effect of the quantity of addition on the densificationand the mechanical properties of these materials was done. Under the sametemperature, with the increase of the quantity of the additions, the density hasincreased, and the variation of the mechanical properties of these materialsdepended on the density and the quantities of the second-phase particle and intercrystalline phase of these materials…
Key words: fine-crystalline Si_3N_4/Al_2O_3; composite ceramic; sintering process addition; density; mechanical property

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