In situ synthesis of Mo 5Si 3 particle reinforced Si 3N 4 composite with crystallized grain boundary phase of Yb 2Si 2O 7

Abstract

Mo 5Si 3 particle reinforced Si 3N 4 composite with crystallized grain boundary phase of Yb 2Si 2O 7 was synthesized in situ by sintering a green compact that contained Si 3N 4, MoO 3 and Yb 2O 3 powders. The reaction between Si 3N 4, MoO 2 and Yb 2O 3 at high temperature generated the Mo 5Si 3 particles and the grain boundary phase of Yb 2Si 2O 7 simultaneously. Mo 5Si 3 particles resided at the grain boundary phase of Yb 2Si 2O 7, and had an average size of 0.2 μm. In the Mo 5Si 3–Yb 2Si 2O 7–Si 3N 4 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 Mo 5Si 3 particles, the grain boundary phase of Yb 2Si 2O 7 and Si 3N 4 grain. The thickness of thin amorphous films at such interfaces was about 0.6 nm. Because the SiO 2 needed to generate Yb 2Si 2O 7 was supplied by the in situ reaction between MoO 2 and Si 3N 4, 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.