α-SiAlON ceramics with elongated grain morphology using an alternative sintering additive

Abstract

In this work, the use of a natural yttrium oxide and rare earth oxide solid solution (CRE 2O 3) as stabilizers of the α-Si 3N 4 phase to form α-SiAlON has been investigated. This oxide mix is produced at FAENQUIL-DEMAR, at a cost of only 20% of pure commercial Y 2O 3. Two α-SiAlONs using pure Y 2O 3 or CRE 2O 3 have been prepared, using mixes of 20% by volume of a molar fraction of 9:1 of AlN to Y 2O 3 or AlN to CRE 2O 3, respectively, with 80% α-Si 3N 4. Samples were gas pressure-sintered at 1900 °C, under 1.5 MPa of N 2 for 60 min. Both compositions yielded α-SiAlON ceramics with high relative densities (98% t.d.), hardness of 18 GPa and fracture toughness of 5 MPa m 1/2, with homogeneous microstructures composed of elongated α-SiAlON grains with aspect ratios of 5. It is concluded that the mixed rare earth concentrate (CRE 2O 3) can be used to produce α-SiAlON ceramics with similar microstructures and mechanical properties of α-SiAlON ceramics fabricated using pure Y 2O 3, but with the advantage of its lower production cost.