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.

Preparation and mechanical properties of machinable alumina/mica composites

“…The bending strength was 400-450 MPa, which were the same level as that of the conventional monolithic alumina ceramics while the fracture toughness was 3.7-3.9 MPa·m 0.5 , which were little higher than that of the conventional monolithic alumina ceramics. The Vickers hardness was [11][12][13][14] GPa, which was the same level as that of zirconia ceramics. 9.…”

Fabrication and properties of ZrB2–SiC–BN machinable ceramics

“…8 Among those materials, h-BN, which exhibits high thermal conductivity and high melting point, is regarded as a suitable and effective interface material since the cleavage plane of h-BN facilitates crack propagation and decreases the cutting resistance during machining. [9][10][11][12] Besides these, the similar crystal structures of BN and ZrB 2 ensure the good chemical compatibility between them. Therefore, ZrB 2 -SiC-BN system may be a good candidate material for high temperature ceramics with excellent machinability and mechanical properties.…”

Investigation on the preparation and machinability of the B4C/BN nanocomposites by hot-pressing process

“…On the other resistance property and good machinability (Kusunose et al, , 2002a(Kusunose et al, ,b, 2005Niihara, 1991). Niihara and Kusunose reported that they have prepared the Si 3 N 4 /BN nanocomposite powders by the chemical reaction of H 3 BO 3 and CO(NH 2 ) 2 on the surface of Si 3 N 4 particles at high temperature, and the Si 3 N 4 /BN nanocomposites were fabricated by the hot-pressing process (Kusunose et al, , 2002a. They also have fabricated the Al 2 O 3 /BN nanocomposites by the same process (Kusunose et al, 2005).…”