Compositional identification of the intergranular phase in liquid phase sintered SiC

Abstract

A model system consisting of coarse SiC (32–160 μm) as starting powder and Y 2 O 3 and AlN as sintering additives was liquid phase sintered. Coarse-grained starting powder led to large intergranular phase regions which allowed an accurate determination of the chemical composition by wavelength-dispersive X-ray microanalysis (WDS). When N 2 was used as sintering atmosphere, a N-rich amorphous phase (about 44 at.% N) was identified by WDS to be the main triple-junction phase in the sintered SiC ceramics, while three further crystalline intergranular phases were AlN, Y 2 SiN 4 O 3 and an O-rich phase (Y 10 Al 2 Si 3 O 18 N 4 ). The overall O content was found to be reduced in comparison to the initial powder composition. The incorporation of N from the sintering atmosphere into the intergranular phase and a subsequent carbothermal reduction are believed to be responsible for the removal of O and the formation of the N-rich amorphous phase.