Preparation, microstructure, stability in magnesium metallurgy environment of SiC composites

The α-SiC/SiO2 and α-SiC/β-SiC composites were prepared by pressureless sintering. The physical properties and microstructure were characterized. Compared to SiO2, the in situ formation of β-SiC was more beneficial to density of α-SiC composites. The stability in magnesium metallurgy environment of different SiC composites was investigated. The SiC composites are corroded by two ways: SiC activated oxidation and grain boundary corrosion by slag. In low oxygen environment, the activated oxidation of SiC forms SiO, resulting in the destruction of SiC surface structure. The CaO and other oxides in the slag are easy to react with SiO2, which continuously corrodes the grain boundaries and eventually leads to the continuous shedding of SiC grains. In particular, the conversion of β-2CaO·SiO2 to γ-2CaO·SiO2 results in volume expansion of about 12%, resulting in grain boundary expansion and structural failure. The α-SiC/β-SiC composites had higher density and better corrosion resistance to magnesium slag.