Grain boundary phase and microstructural study on non-oxide Si3N4 ceramics

Engineering ceramics are often difficult to prepare for observation because of their hardness, wear resistance and chemical inertness. Different silicon nitride containing ‎Y2O3 and Al2O3 are prepared and etched using several different techniques and the most efficient methods are identified. The microstructure and grain-boundary composition were examined by electron microscopy (SEM, TEM), electron diffraction and energy-dispersive X-ray microanalysis. A method has been developed to quantify microstructure consisting of elongated, rod like -grains to discuss the interdependence between starting materials composition, processing condition, microstructure and resulting mechanical properties of dense Si3N4 materials. It is shown that post-sintering heat-treatment in air in the temperature between 1100-1450 C results in substantial crystallisation of the glassy phase.