Long term oxidation behaviour of liquid phase pressureless sintered SiC–AlN ceramics obtained without powder bed

Abstract

This paper describes the results of the investigation of the oxidation behaviour of 50 wt.% SiC–50 wt.%AlN composites obtained by means of pressureless sintering with Y 2O 3 as sintering-aid and without using a powder bed to limit the weight loss. Sintered bodies show high density (>98%T.D.) and the microstructure reveals a matrix composed by SiC–AlN solid solution with Y 10Al 2Si 3O 18N 4 as grain boundary phase. This material exhibits a parabolic oxidation kinetic in the temperature range 1200–1500 °C. Long term oxidation (200 h) induces the formation of a protective oxide scale, composed by mullite, cristobalite and yttrium disilicide, up to 1400 °C. At higher temperature (1500 °C), SiC oxidation behaviour changes from “passive” to “active” and the oxide layer consequently shows porosity due to the formation of gaseous species like SiO and CO.