New Strategies for Preparing NanoSized Silicon Nitride Ceramics

Abstract

We report the preparation of nanosized silicon nitride (Si 3 N 4 ) ceramics via high‐energy mechanical milling and subsequent spark plasma sintering. A starting powder mixture consisting of ultrafine β‐Si 3 N 4 and sintering additives of 5‐mol% Y 2 O 3 and 2‐mol% Al 2 O 3 was prepared by high‐energy mechanical milling. After milling, the powder mixture was mostly transformed into a non‐equilibrium amorphous phase containing a large quantity of well‐dispersed nanocrystalline β‐Si 3 N 4 particles. This powder precursor was then consolidated by spark plasma sintering at a temperature as low as 1600°C for 5 min at a heating rate of 300°C/min. The fully densified sample consisted of homogeneous nano‐Si 3 N 4 grains with an average diameter of about 70 nm, which led to noticeable high‐temperature ductility and elevated hardness.