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

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 Y2O3 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 Y10Al2Si3O18N4 as grain boundary phase. This material exhibits a parabolic oxidation kinetic in the temperature range 1200-1500 degrees C. Long term oxidation (200 h) induces the formation of a protective oxide scale, composed by mullite, cristobalite and yttrium disilicide, up to 1400 degrees C. At higher temperature (1500 degrees 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. (c) 2005 Elsevier Ltd. All rights reserved.