Effect of ferrosilicon additive and sintering condition on microstructural evolution and mechanical properties of reaction-bonded SiC refractories

Abstract

In the refractories processing, developing low cost methods and simplifying the existing technology for manufacturing refractories are always desirable. In this perspective, heat treating in a graphite bed in combination with ferrosilicon sintering additive were used to fabricate self-reaction silicide/nitride-bonded SiC refractories. The influence of ferrosilicon (0–5wt%) on the microstructure evolution and mechanical properties was investigated. On the one hand ferrosilicon presented between the SiC aggregates boundaries, which indicated that ferrosilicon played a dominant role in the densification of materials. On the other hand the formation of Si3N4 whiskers with tips was encouraged in the presence of ferrosilicon; which suggested that ferrosilicon had catalytic effects on the formation of Si3N4 whiskers via a vapor-liquid-solid (VLS) mechanism. Furthermore, the cold modulus of rupture (CMOR) increased with ferrosilicon content up to 2.5wt% followed by slight decrease in strength after further increase in the amount of additive. The observed improvement can be attributed to the densification and formation of a new reinforced phase (Si3N4 whiskers with tips). At last, a SiCxOy bonding layer between SiC aggregate and matrix could be distinguished, and a mechanism to explain the formation was suggested.