Synthesis of Si3N4/SiC reaction-bonded SiC refractories: The effects of Si/C molar ratio on microstructure and properties

Si3N4/SiC reaction-bonded SiC refractories have been fabricated on the basis of the microstructure design concept by introducing a binary-phases binding system. The influence of Si/C molar ratio on phase transformation, microstructure and mechanical properties was studied systematically. Thermodynamic analysis result proved the microstructure design was feasible under 0.03 MPa pressure of N2 and the selected sintering temperature. In-situ grown SiC nano-whiskers/granule and lamellar Si3N4 were both observed in the matrix. The specimen with 2:1 Si/C molar ratio possessed highest cold modulus of rupture (28.27 MPa) but showed low toughness. The strength and toughness of such materials were controlled by two main factors, such as SiC grain boundary binding morphology and in situ grown of SiC in the matrix. The different mechanisms occurred predominantly to meet diverse practical cases and caused to various mechanical properties of final products. The corresponding strengthening and toughening mechanisms were explained in this paper.