Effect of microstructural variables on the erosion of silicon nitride ceramics

Silicon nitride ceramics with three different microstructures were prepared using three different silicon nitride powders and β-silicon nitride whiskers in order to study their erosion characteristics. Samples with a coarse microstructure were prepared by using a commercially available silicon nitride powder seeded with the whiskers. Samples with fine microstructures were obtained using fine silicon nitride powders that had been milled in toluene or in distilled water. The powder milled in toluene gained both carbon and oxygen during milling. Heating the powder at 1673 K for 10 h in a flowing nitrogen atmosphere reduced carbon and oxygen contents to the level of as-received powder. The powder milled in distilled water gained a significant amount of oxygen during milling, and silicon oxynitride (Si₂N₂O) was detected by X-ray diffraction analysis (XRD) from the sample sintered with it. The sample sintered with the powder milled in distilled water showed the finest microstructure and the lowest erosion rate among the samples. Erosion occurred mainly by dislodgment of grains.