Fabrication of β-sialon nanoceramics by high-energy mechanical milling and spark plasma sintering

Abstract

A single-phase β-sialon nanoceramic, Si5AlON7, has been prepared by high-energy mechanical milling, followed byspark plasma sintering. After milling, the starting powder mixture(Si3N4, AlN,Al2O3) wasmostly transformed into an amorphous phase that contains a large number of well-dispersed nanocrystallineβ-Si3N4 particles. Milling promoted the mixing and reaction among the starting powders;β-sialon grains with the designed composition were formed directly throughprecipitation from the homogeneous amorphous phase on the nanocrystallineβ-Si3N4 particles. Milling also improved the sintering ability of the startingpowders, so the densification temperature was lowered by about100 °C compared with that for as-received powders. Particle rearrangement was the main densificationmechanism for the milled powders. A homogeneous microstructure composed of equiaxedβ-sialon grains with a diameter of about 50 nm was obtained after sintering at1550 °C for 5 min.