Research On Spark Plasma Sintering Of Fine-crystalline Al₂O₃/Si₃N₄ Composite Ceramics

Al₂O₃-matrixed ceramics with Si₃N₄ contents from 0 wt.% to 15 wt.% have been prepared by spark plasma sintering(SPS) in this paper. The sample's density hardlness toughness X-ray diffraction(XRD) , scanning electron microscope(SEM) and transmission electron microscope(TEM) analysis have been tested. The mechanical properties micromorphology and grain boundary microstructure of the composite ceramics were systematically studied. Then the relationship of different components sintering parameters microstructures, properties were discussed. At last the mechanism of sintering and toughening of the materials have been investigated.From the results, we could find that at 1450℃ 1500℃ and 1550℃, the sample's relative density and hardness were appreciably decreased as the temperature increased. At 1450℃,the sample's density and hardness were better when the contents of silicon nitride were under 0.75 wt.% and 10 wt.%. The better values were 100%, 20.159GPa and 97.2% 17.943GPa respectively.When the content of silicon nitride was 10 wt.%, the toughness was the highest, which was 5.261MPa · m¹/2. The toughness improved about 31.1% in contrast with the pure aluminum oxide, which was 4.014 MPa · m¹/2. While contents of silicon nitride rise continuously, the mechanical properties decreased rapidly.The results show that the densification process was controlled by the mechanism of liquid phase sintering. The densification process began with the appearance of liquid phase in sintering body at about 1200℃ and ended at about 1400℃. During that period, the aluminum oxide and the silicon nitride reacted finally formed β'-Sialon., at last the inter-grain and the boundary compound structure was gained. The mechanism was dissolution-deposition and there were only aluminum oxide and β'-Sialon in the final sample. Transgranular-fractured was mainly observed, which was helpful to the toughness.These basic researches are important for optimizing the processing techniques, by which Al₂O₃/Si₃N₄ ceramic materials with excellent properties can be fabricated.