Ytterbium-stabilized -sialon ceramics

Abstract

Dense, Yb-doped -sialon ceramics of the composition , with , together with some Yb-based - and -sialon ceramics containing an excess of glassy phase, have been prepared by hot-pressing at . These materials were subsequently heat-treated in the temperature range for different periods. It was found that Yb-doped -sialon forms within a wide composition region, with x ranging from 0.3 to more than 1.0, and that -sialon is stable over a large temperature interval and during heat treatment times of up to 30 days. The -sialon phase coexists with a liquid phase at and with crystalline phases such as the Yb garnet and/or J phase at . Further heat treatment at revealed that initially (during the first 24 h) the -sialon phase reacts with the residual liquid grain-boundary phase, yielding a material which contains an Yb-stabilized garnet phase, besides the -sialon phase, but no glassy phase. This phase assembly is stable upon further heat treatment (30 days). Samples containing Yb-doped -sialon in conjunction with an amorphous intergranular phase show very high hardness and fracture toughness in the range of at room temperature, and mechanical data in the same range were obtained for samples exposed to prolonged heat treatment at . Elongated -sialon grains were found in samples with high x values, but their presence did not affect the mechanical properties significantly.