Fracture characteristic of a (Si–Al–O–N)–SiC composite studied by transmission electron microscopy

The microstructure and fracture characteristic of a pressureless-sintered (Si–Al–O–N)–6 wt% SiC composite have been investigated by a combination of transmission electron microscopy and microindentation fracture technique. SiC particles of nanometre size were dispersed in Si–Al–O–N grains and, at grain boundaries, were associated with strong strain fields. Si–Al–O–N grain boundaries were formed with an amorphous layer about 2 nm thick. However, interfaces between Si–Al–O–N and SiC embedded in the Si–Al–O–N grains were directly joined without any amorphous layer. The main fracture mode was an intergranular type, but some transgranular fracture by the dispersion of nanometre-sized SiC in the Si–Al–O–N grains are also observed at the crack wake zone. The fracture toughening mechanisms of crack deflection, bridging and microcracking were not observed in the (Si–Al–O–N)–6 wt% SiC nanocomposite system.