Papers by Keyword: Si₃N₄/SiC

Abstract: Effect of different sintering additives on reaction-bonded Si3N4/SiC composite ceramics under pressureless was investigated. Si3N4/SiC composite ceramics were sintered at the temperature 1550 °C under nitrogen atmosphere with different sintering additives Y2O3, Y2O3:Al2O3=1:1, Y2O3:Mg2AlO4 :Mg3(Si4O10)(OH)2: SiO2=5:2:1:1, and ZrO2 by using SiC with different particle sizes, and Si as raw materials. The phases, microstructure and mechanical property were characterized by XRD, SEM, and compressive strength test. The results demonstrated that when the particle gradation consisted of silicon carbide of 74 μm (5 wt.%), 44 μm (10 wt.%) and 0.5 μm(30 wt.%) and silicon powder of 74 μm (42 wt.%), the more dense samples with the bulk density of 2.43 g/cm3 and the higher compressive strength of 324 MPa could be obtained when Y2O3 was used as sintering additives.

Abstract: Effect of sintering temperatures on reaction-bonded Si3N4/SiC composite ceramics under pressureless was investigated. Si₃N₄/SiC composite ceramics were sintered at different temperatures from 1450 to 1700 °C under nitrogen atmosphere by using SiC with different particle sizes, Si and additives Y₂O₃ as raw materials. The phases, microstructure and mechanical property were characterized by XRD, SEM, and compressive strength tests. The results demonstrated that when the particle gradation consists of silicon carbide of 74 μm (5 wt.%), 44 μm (10 wt.%) and 0.5 μm(35 wt.%) and silicon powder of 74 μm (42 wt.%), the more dense samples with the bulk density of 2.43 g/cm³ and the higher compressive strength of 324 MPa could be obtained at the sintering temperature of 1550 °C for 3h as the optimum processing parameters.

Abstract: Self-sealed laminar Si3N4/SiC composites, with different cross-section shapes and various thickness ratios of Si3N4 to SiC, have been fabricated. The laminates consist alternately of thicker Si3N4 layers ranging from 100 to 500µm and thinner SiC layers ranging from 6 to 15µm after sintering. Preliminary results indicate that SiC thin layer forms during sintering according to the reaction Si3N4 + 3C ® 3SiC + 2N2, which is confirmed by X-ray diffraction. An excellent physical and chemical compatibility between Si3N4 and SiC layers was observed. The self-sealed Si3N4/SiC composites not only demonstrate a superb resistance to delamination, usually associated with the plate-form ones, but also show a high damage-tolerance behavior. The laminated Si3N4/ SiC composite with a layer thickness ratio of Si3N4 to SiC of approximately 40 gives the highest value of work of fracture (WOF) of approximately 406 kJ/m3, whereas the highest toughness of 21 MPam1/2 was achieved at the layer thickness ratio of 50. The effects of the relative thickness of Si3N4 and SiC layers on the densification of the laminates are examined and fracture behavior and microstructure of the Si3N4/SiC laminates discussed.

Abstract: Si3N4/SiC composite ceramics were hot-pressed in order to investigate their crack-healing behavior under cyclic stress and the resultant static fatigue strength. Semi-elliptical surface cracks of 100 μm in surface length were made on each specimen. The pre-cracked specimens were crack-healed under a cyclic bending stress of 210MPa in air at 900, 1000, 1100, and 1200 °C. The bending strength and static fatigue strength of the crack-healed specimens were systematically investigated at each healing temperature. The specimens which has been crack-healed and static fatigue-tested at 900 and 1000 °C showed lower static fatigue strength than those tested at 1100 and 1200 °C. Detailed investigation on the fracture surface of static fatigue-tested specimens showed that oxidation of the base material had strong effects on the static fatigue strength. It was found that when the specimens were pre-oxidized in air at 1300 °C, the surface was covered by a protective oxide layer, leading to a significant improvement of static fatigue strength at 900 and 1000 °C.