Effect of sintering atmosphere on the mechanical properties of liquid-phase-sintered SiC

It has been demonstrated that sintering atmosphere (Ar or N2) exerts a strong influence on the microstructural evolution in liquid-phase-sintered (LPS) SiC with oxide additives. N2-atmosphere sintering (β-SiC stating powders) results in LPS SiC with equiaxed-grained microstructures, and “strong” and more viscous nitrogen-containing intergranular phase. In contrast, Ar-atmosphere sintering results in LPS SiC with elongated-grained microstructures, and “weak” and less viscous intergranular phase. This has a profound effect on the room- and high-temperature mechanical properties of LPS SiC. N2–LPS SiC is less “quasi-ductile” under Hertzian indentation, harder, and more brittle. In contrast, Ar–LPS SiC is more “quasi-ductile”, softer, and tougher. At high temperature, N2–LPS SiC is more deformation-resistant, stronger, but fails at lower strains. Ar–LPS SiC, on the other hand, has lower deformation resistance, lower ultimate compressive strength, but higher strain-to-failure. This contrast in the mechanical properties of the two materials is discussed in the context of the microstructures they possess.