Fabrication and Microstructure of Silicon Nitride/Boron Nitride Nanocomposites

摘要

A chemical process for fabrication of Si_3N_4/BN nanocomposite was devised to improve the mechanical properties. Si_3N_4/BN nanocomposites containing 0 to 30 vol% hexagonal BN (h-BN) were successfully fabricated by hot-pressing α-Si_3N_4 powders, on which turbostratic BN (t-BN) with a disordered layer structure was partly coated. The t-BN coating on α-Si_3N_4 particles was prepared by reducing and heating α-Si_3N_4 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 Si_3N_4 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.