Stabilization of α-SiAlONs using a rare-earth mixed oxide (RE 2O 3) as sintering additive

• Published in: Materials research bulletin 2005-07, Vol.40 (7), p.1094-1103
• Main Authors: Santos, C., Strecker, K., Suzuki, P.A., Kycia, S., Silva, O.M.M., Silva, C.R.M.
• Format: Article
• Language: English
• Subjects: A. Ceramics; A. Nitrides; C. X-ray diffraction; D. Crystal structure
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/j.materresbull.2005.03.017

α-SiAlONs are commonly produced by liquid phase sintering of Si 3N 4 with AlN and Y 2O 3 as additives. The formation of the α-SiAlONs using a mixed oxide (RE 2O 3), containing yttria and rare-earth oxides, as an alternative additive was investigated. Dense α-SiAlONs were obtained by gas-pressure sintering, starting from α-Si 3N 4 and AlN–Y 2O 3 or AlN–RE 2O 3 as additives. The mixed oxide powder RE 2O 3 was characterized by means of high-resolution synchrotron X-ray diffraction and compared to Y 2O 3. The X-ray diffraction analysis of the mixed oxide shows a pattern indicating a true solid solution formation. The Rietveld refinement of the crystal structure of the sintered α-SiAlON using AlN–RE 2O 3 as additive revealed a similar crystal structure to the α-SiAlON using AlN–RE 2O 3 as additive. The comparison of the microstructures of the both α-SiAlONs produced using pure Y 2O 3 or RE 2O 3, revealed similar grain sizes of about 4.5 μm with aspect ratios of about 5. Both materials show also similar mechanical properties, with hardness of 18.5 GPa and fracture toughness of 5 MPa m 1/2. It could be, thus, demonstrated that pure Y 2O 3 can be substituted by the rare-earth solid solution, RE 2O 3, in the formation of α-SiAlONs, presenting similar microstructural and mechanical properties.