Fabrication and characterization of SPS sintered SiC-based ceramic from Y3Si2C2-coated SiC powders

The Y3Si2C2 coating was in-situ synthesized on the surface of SiC powders to form SiC-Y3Si2C2 core-shell structure by using a molten salt technique. Phase diagram calculations on Si-Y-C ternary phase at different temperatures well illustrated that the Y3Si2C2 phase can be stable with SiC but will be in liquid state at 1560 degrees C. The liquid Y3Si2C2 explained the enhanced consolidation of SiC ceramics and its disappearance after spark plasma sintering. Such Y3Si2C2 coating could not only effectively improve the sintering, but also their mechanical and thermal properties of resultant ceramics. Typically, at 1700 degrees C, the bulk SiC ceramic presented a mean grain size of 2.5 um and relative density of 99.5% when the molar ratio of Y to SiC is 1:4 in molten salts; the Young's modulus, indentation hardness and fracture toughness measured by indentation test were 451.7 GPa, 26.3 GPa and 7.9 M Pam(1/2), respectively; the thermal conductivity is about 145.9 W/(m K). Excellent thermal and mechanical properties could be associated with the fine grain size, optimized phase composition and improved grain boundary structure.