Microstructure and oxidation behaviour of SiC fibre-reinforced Si3N4-AlN-Al2O3-Y2O3 matrix composites

Abstract

A series of SiC fibre-reinforced Si 3 N 4 -AlN-Al 2 O 3 -Y 2 O 3 matrix composites with different matrix compositions are fabricated by slurry infiltration followed by hot pressing at 1600 • C for 30 min. The diffusion of yttrium and aluminium into fibres is apparent during the high temperature processing. All the as-processed composites show fracture with fibre pull-out. After heat treatment in air at 1000 • C for 60 min, composites with minimal Y 2 O 3 and Al 2 O 3 in the matrix composition demonstrate the fracture behaviour with most extensive fibre pull-out. Composites with the highest aluminium and yttrium oxide content form an yttrium-aluminium-garnet phase and an aluminosilicate glassy phase. The latter phase provides an oxygen diffusion path, resulting in the removal of the carbon-rich interphase by oxidation. This results in catastrophic fracture without fibre pull-out after heat treatment of the composite in air.