Fabrication and mechanical properties of β-sialon–FexSiy–CNTs composites

Silicon nitride composites were fabricated by adding Fe3Al and carbon nanotubes and hot-pressing at a low sintering temperature of 1600 °C. The resulted composites were characterized by X-ray diffraction, Fourier-transform infrared spectrum, and field emission scanning electron microscopy. It was found that the Fe3Al could react with Si3N4 to form the series of compound of FexSiy, and CNTs could keep chemical stability in the system. Mechanical properties of the composites were also investigated. For Fe3Al as the additive, the relative density could reach to 93.6 % with the maximum hardness of 15.7 GPa. When the Fe3Al and CNTs were added into matrix simultaneously, the relative density reached to 92.6 %, and the maximum fracture toughness was 6.7 MPa m1/2. Finally, the toughening mechanism of Fe3Al and CNTs in sialon composites, containing crack deflection and bridging, and nanotubes pullout and bridging, were also discussed.