Fabrication and Microstructure of Silicon Nitride/Boron Nitride Nanocomposites

Abstract

A chemical process for fabrication of Si3N4/BN nanocomposite was devised to improve the mechanical properties. Si3N4/BN nanocomposites containing 0 to 30 vol% hexagonal BN (h‐BN) were successfully fabricated by hot‐pressing α‐Si3N4 powders, on which turbostratic BN (t‐BN) with a disordered layer structure was partly coated. The t‐BN coating on α‐Si3N4 particles was prepared by reducing and heating α‐Si3N4 particles covered with a mixture of boric acid and urea. TEM observations of this nanocomposite revealed that the nanosized hexagonal BN (h‐BN) particles were homogeneously dispersed within Si3N4 grains as well as at grain boundaries. As expected from the rules of composites, Young's modulus of both micro‐ and nanocomposites decreased with an increase in h‐BN content, while the fracture strength of the nanocomposites prepared in this work was significantly improved, compared with the conventional microcomposites.