Effect of Carbon Source on Microstructure and Mechanical Properties of Silicon Carbide Fabricated by Two-Step Reaction Sintering

ABSTRACT: Reaction-bonded silicon carbide (RBSC) ceramics prepared by gel casting and two-step sintering were investigated. Three active carbon sources of petroleum coke (PC), carbon microspheres (MC), and nano-carbon black (CB) were compared in terms of slurry rheology, preform characteristics, sintered microstructure, and mechanical properties. With the active powders of PC and MC, the large particle size resulted in low density of the preform and un-uniform distribution of active carbon. CB addition yielded the highest slurry viscosity, the highest preform density, and the highest carbon density of 1.00 g·cm⁻³. The higher carbon density and more uniform active carbon translated into the highest SiC phase content and the lowest residual Si after sintering, attributed to the uniform active carbon distribution. A high-performance RBSC ceramic with a density of 3.12 g·cm⁻³, bending strength of 512 MPa, and Vickers hardness of 2386.6 HV was achieved. The corresponding phase composition was 94.28 vol.% SiC, only 2.22 vol.% residual Si, which is significantly lower than that of conventional RBSC. These results highlight the critical role of active carbon source selection in optimizing RBSC performance through microstructural refinement and residual phase control.