Pressureless sintered SiAlON with low amounts of sintering aid

Abstract

β′-SiAlONs of compositions Si_2.6Al_0.393Y_0.007O_0.4N_3.6 and Si_2.6Al_0.384Y_0.014O_0.4N_3.6 were pressureless sintered from mixtures of Y₂O₃ and separately milled β-Si₃N₄, AlN, and SiO₂. On sintering, the carbon content of these SiAlONs was reduced to negligible levels and their oxygen content was also proportionately reduced, presumably due to reaction of carbon with SiO₂. These SiAlONs had densities in excess of 98% of theoretical, four-point bend strengths of 460 and 155 MN m⁻² at r.t. and 1400° C, respectively, and 1400° C oxidation rates lower than those reported in the literature for hot-pressed Si₃N₄ and for a similar but stronger SiAlON with 2.5 wt % Y₂O₃. These results indicate that increasing the Y₂O₃ content of SiAlONs increases their strength but decreases their oxidation resistance.