In situ synthesis of Mo5Si3 particle reinforced Si3N4 composite with crystallized grain boundary phase of Yb2Si2O7

Mo5Si3 particle reinforced Si3N4 composite with crystallized grain boundary phase of Yb2Si2O7 was synthesized in situ by sintering a green compact that contained Si3N4, MoO3 and Yb2O3 powders. The reaction between Si3N4, MoO2 and Yb2O3 at high temperature generated the Mo5Si3 particles and the grain boundary phase of Yb2Si2O7 simultaneously. Mo5Si3 particles resided at the grain boundary phase of Yb2Si2O7, and had an average size of 0.2 μm. In the Mo5Si3–Yb2Si2O7–Si3N4 composite, most of grain boundary junctions were completely crystallized, but a small amount of amorphous phases were detected from some grain pockets and the interfaces between Mo5Si3 particles, the grain boundary phase of Yb2Si2O7 and Si3N4 grain. The thickness of thin amorphous films at such interfaces was about 0.6 nm. Because the SiO2 needed to generate Yb2Si2O7 was supplied by the in situ reaction between MoO2 and Si3N4, the densification and the crystallization of the grain boundary phase were promoted, and a dense composite with relatively high strength was obtained by using a gas pressure sintering method.