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

摘要

A single-phase betas-sialon nanoceramic, Si_5AlON_7, has been prepared by high-energy mechanical milling, followed by spark plasma sintering. After milling, the starting powder mixture (Si_3N_4, A1N, Al_2O_3) was mostly transformed into an amorphous phase that contains a large number of well-dispersed nanocrystalline beta-Si_3N_4 particles. Milling promoted the mixing and reaction among the starting powders; beta-sialon grains with the designed composition were formed directly through precipitation from the homogeneous amorphous phase on the nanocrystalline beta-Si_3N_4 particles. Milling also improved the sintering ability of the starting powders, so the densification temperature was lowered by about 100 deg C compared with that for as-received powders. Particle rearrangement was the main densification mechanism for the milled powders. A homogeneous micro structure composed of equiaxed beta-sialon grains with a diameter of about 50 nm was obtained after sintering at 1550 deg C for 5 min.