Effects of in situ Mg-Sialon and -Sialon on the microstructure and properties of MgAl₂O₄-SiC composites

MgAl2O4-SiC composites were prepared under flowing nitrogen at 1500 degrees C by using MgAl2O4 powder, SiC powder, Al powder and Si powder as raw materials. Through microstructural observation and analysis, the effects of in situ Mg-Sialon and beta-Sialon with different amounts of Si powder addition were investigated in this paper. The results show that the samples without Si addition main contained MgAl2O4, SiC and well development plate structure Mg-Sialon phase. After addition of Si powder, not only the above three phases appeared, but also beta-Sialon phase appeared. Meanwhile, with increasing Si contents, the content of beta-Sialon phase increased and samples were more dense, limiting the development of the plate structure Mg-Sialon phase. With increasing Si content from 0 wt% to 20 wt%, the apparent porosity shows decreased trend, while the bulk density and cold module of rupture show increased. The samples with 20 wt% Si addition can get the minimum apparent porosity (33.5 %), maximum bulk density (2.13 g center dot cm(-3)) and cold module of rupture (87.0 MPa). Besides, the formation mechanism of Mg-Sialon and beta-Sialon was discussed in detail and the role of Si was elucidated.