Stabilization of α-SiAlONs using a rare-earth mixed oxide (RE2O3) as sintering additive

α-SiAlONs are commonly produced by liquid phase sintering of Si3N4 with AlN and Y2O3 as additives. The formation of the α-SiAlONs using a mixed oxide (RE2O3), containing yttria and rare-earth oxides, as an alternative additive was investigated. Dense α-SiAlONs were obtained by gas-pressure sintering, starting from α-Si3N4 and AlN-Y2O3 or AlN-RE2O3 as additives. The mixed oxide powder RE2O3 was characterized by means of high-resolution synchrotron X-ray diffraction and compared to Y2O3. 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-RE2O3 as additive revealed a similar crystal structure to the α-SiAlON using AlN-RE2O3 as additive. The comparison of the microstructures of the both α-SiAlONs produced using pure Y2O3 or RE2O3, 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 m1/2. It could be, thus, demonstrated that pure Y2O3 can be substituted by the rare-earth solid solution, RE2O3, in the formation of α-SiAlONs, presenting similar microstructural and mechanical properties.