Phase evolution and microstructure of SiC–MgAl2O4–Al composites sintered in argon atmosphere at 1450 °C: Reactions in Al–O–C system

Abstract

SiC–MgAl2O4–Al composites were prepared using SiC, MgAl2O4, corundum and Al powder as raw materials by firing at 1450 °C in flowing argon. The effects of binders on phase composition and microstructure evolution were investigated. The results show that the external of specimens with thermosetting phenolic resin and water soluble resin as binders both contained SiC, MgAl2O4, corundum and Al4O4C phases. In center of the specimens, Al4C3 and Al2OC phases appeared in the thermosetting phenolic resin bonded specimens while Al4O4C and Al2OC phases appeared in the water soluble resin bonded specimens. The microstructure shows that MgAl2O4 whiskers generated at surface of both specimens through gas-gas reaction. As for the specimens with thermosetting phenolic resin as binder, the residual carbon (decomposed from phenolic resin) and Al in the external of the specimen react with O2 to form CO and Al2O, which promoting the formation of plate-like Al4O4C. In the center of the specimen, Al4C3, Al2O3 and Mg(g) formed. Mg(g) migrates to outside and transforms to MgAl2O4 whiskers, and a part of Al4C3 transform to columnar Al2OC. Al2OC whiskers can also be generated through the reaction among Al2O, CO and C. Compared with the thermosetting phenolic resin bonded specimens, Al at external of the water soluble resin bonded specimen reacts with O2 to form Al2O3, which further transforms to particle Al4O4C. In the center of water soluble resin bonded specimen, a little Al4C3 formed and can totally transform to Al4O4C and Al2OC.