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High Temperature Compressive Deformation of Silicon Nitride and Carbide Ceramic Composites

Author: ZhangLei
Tutor: YeFeng
School: Harbin Institute of Technology
Course: Materials Science
Keywords: Si3N4 based ceramics SiC based ceramics spark plasma sintering (SPS) high temperature compressive deformation
CLC: TQ174.1
Type: Master's thesis
Year: 2010
Downloads: 123
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Abstract


Dense BAS/Si3N4 composites, SiAlON ceramics, and BAS/SiC composites were fabricated by spark plasma sintering （SPS）. The high temperature compressive deformation behaviour and its effects on the microstructures and mechanical were studied.Si3N4 composites containing different amount of BAS started to deform at about 1580℃. As the BAS content increases, a faster compressive deformation with a maximum compressive strain rate on the order of 10-3s-1 were achieved at lower temperature （1600℃）. The 40wt%BAS/Si3N4 composite exhibited a maximum strain rate of 1.5×10-2s-1 when deformed under 1600℃for 5min. This high strain rate demonstrates superplasticity. Texturing of the elongatedβ-Si3N4 grains, which tended to align along the surface perpendicular to the uniaxial pressure, was observed.5wt%BAS/RE-α-SiAlONs doped with different rare-earth ions began deformation at 1500℃, and achieved a maximum strain rate of 10-3s-1 at 1630℃, although much less BAS phase was present. The deformation capability of the materials was related to the amount of the interface phases. Yb-SiAlON had a much clearer interface, hence lesser strain and slower strain rate. The strain of the material was accomplished by rotation and sliding of elongatedα-SiAlON grains through the deformation process. No significant difference in microstructures before and after deformation has been observed.Y1010-α-SiAlON using extra rare-earth oxides as the sinter additive also achieved a remarkable compressive strain rate. The maximum reached 10-3s-1 at 1630℃. The compressive deforming directly related with the contents of the sintering additives. Both the rotation and growth of elongatedα-SiAlON grains contributed to the deformation process, resulting in larger grain size as well as larger aspect ratio.SiC composite containing different amount of BAS started deforming at 1590℃. 40wt%BAS/SiC reached maximum compressive deformative rate of 6.1×10-3s-1 at 1600℃. Due to the equiaxedα-SiC grains within the composite, no anisotropy were developed. The equiaxedα-SiC grains had less resistance when moving in the viscous liquid formed at the high temperatures, and the materials showed a better compressive deformation capability in comparison with BAS/Si3N4 composites, in spite of the much larger micron grain sizes.

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CLC: > Industrial Technology > Chemical Industry > Silicate > Ceramic Industry > Basic theory
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