Fabrication of silicon nitride/ boron nitride nanocomposite powder

摘要

Si3N4/BN nanocomposite powders with the mi-crostructure of the micro-sized a-Si3N4 particles coated with nano-sized BN particles were synthesized via the chemical reaction of boric acid, urea, and a-Si3N4 powder in a hydro-gen gas. The results of XRD, TEM, and selected area elec-tron diffraction showed that amorphous BN and a little amount of turbostratic BN(t-BN) were coated on Si3N4 parti-cles as the second phase after reaction at 1100℃. After re-heating the composite powders at 1450℃ in a nitrogen gas, the amorphous and turbostratic BN is transformed into h-BN. These nanocomposite powders can be used to prepare Si3N4/BN ceramic composites by hot-pressing at 1800℃, which have perfect machinability and can be drilled with normal metal tools.