Papers by Author: Kentarou Chihara

Abstract: The high-temperature deformation of dense nano-sized Ca-α SiAlON and submicron- sized β-SiAlON polycrystals were investigated by compression tests. These polycrystals were fabricated from Ca-α SiAlON and β-SiAlON nano powders respectively, and contained almost no intergranular glass phase. Both SiAlONs exhibited large plastic deformations with the stress exponent n ~1 in the higher stress region, and n ~2 in the lower stress region. Shear-thickening creep (n < 1), which has been reported in liquid contained SiAlONs, was not observed.

Abstract: High-strain-rate superplasticity and low-temperature superplasticity are favorable for making the use of superplastic forming for engineering ceramics even more wide spread. In this study, a silicon nitride based nanocomposite was developed for the purpose of improving the superplasticity. An amorphous powder was prepared by mechanical alloying of silicon nitride and metal titanium. A Si3N4-Si2N2O-TiN nanocomposite was fabricated by hot isostatically pressing the amorphous powder compact. A compression test was performed in the temperature range of 1573 K to 1873 K. The nanocomposite could be deformed at a strain rate of 10-2s-1, which was more than 100 times faster than that available for conventional superplastic Si3N4 at 1873 K. Furthermore, the nanocomposite was superplastically deformed in compression at low temperatures from 1573 K to 1673 K. The stress exponent and the activation energy of the nanocomposite were close to those of submicron-silicon nitride.