High Temperature Compressive Deformation Of Silicon Nitride And Carbide Ceramic Composites

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.