Microwave energy at 2.45 GHz has been used to sinter silicon nitride in times of between 30 and 120 minutes to form a dense product with an average grain size of 0.35 μm and substantially improved uniformity of properties over all commercial silicon nitrides and sialons investigated.
A comparison between microwave and conventionally sintered parts of the same density showed the average mechanical properties to be the same for both sintering techniques, but revealed an improvement in the uniformity of mechanical properties of the microwave sintered products.
Silicon nitride components with 5% Al2O3 and 5% Y2O3 as sintering aids, has been sintered to a density of approximately 97% of theoretical. Hipping of these components at 1800 °C for 60 minutes, resulted in the complete removal of residual porosity. Dense components were evaluated in machining tests against commercial ceramic cutting tools. The results show a reduction in wear rate of batter than 10% for microwave sintered Sl3N4 in turning and milling operations on cast iron at a cutting speed of 2000 surface feet per minute.