The microstructure of an yttria-doped hot-pressed silicon nitride

A thorough knowledge of a materialʹs microstructure is an essential starting point from which material development and property characterisation can be undertaken. This paper discusses the importance of combining different techniques, namely X-ray diffractometry, scanning electron microscopy and transmission electron microscopy for gaining a better understanding of the complex microstructure of commercially available Si3N4-based ceramics. Microstructural analyses of a commercial hot-pressed silicon nitride densified with the aid of 9.0 wt% Y2O3 and 1.7 wt% Fe2O3 revealed that this material consists primarily of prismatic hexagonal grains of β-Si3N4 surrounded by a crystalline intergranular phase identified as Y10(SiO4)6N2 (also known as H-phase), the volume fraction of which was estimated to be about 15%. By means of electron diffraction pattern analysis in a conventional TEM some pockets of YNSiO2 (known as K-phase) were identified. TEM analyses also revealed that the material contains both iron silicides (FeSi2) and silicon carbide (SiC) particles as inclusions.