Preparation, oxidation property and mechanism of Si3N4/O′-SiAlON composite ceramics

Abstract

The applications of Si3N4 ceramics were significantly restricted because of the disastrous failure resulted from the oxidation weight gain. The generation of O′-SiAlON could effectively address this issue. The effect of N2 gas pressure on the phase evolution of the Si3N4/O′-SiAlON was studied. It was found that high N2 gas pressure (3 MPa) was more favorable for the formation of the O′-SiAlON than low N2 gas pressure (0.6 MPa). Furthermore, the effects of SiO2 content on the phase evolution, microstructure, oxidation properties and mechanism of the Si3N4/O′-SiAlON ceramics were investigated. The results revealed that the relative content of the O′-SiAlON phase evidently enhanced from 0 wt% to 18.15 wt%, and the bulk density decreased from 3.01 g/cm−3 to 2.62 g/cm−3 with an increase in SiO2 from 0 wt% to 12.5 wt%. Additionally, the weight gain, oxide layer thickness and roughness similarly reduced from 2.02 mg/cm2 to 0.85 mg/cm2, 133.87 μm to 2.31 μm and 21.91 μm to 6.34 μm, respectively. The addition of SiO2 could also reduce bubbles and cracks formation and hinder the diffusion of Al and Y elements from the interior to the surface. Finally, the oxidation resistance mechanism was mainly credited to the pinning effect of O′-SiAlON phases at the grain boundaries.