Densification behavior and mechanical properties of pressureless-sintered silicon carbide ceramics with alumina and yttria additions

Abstract

SiC powders were pressureless sintered to about 98% of the theoretical density by using 10 wt.% (Al 2O 3 + Y 2O 3) as sintering additives. The densification mechanism was attributed to liquid-phase sintering due to the formation of a eutectic liquid between Al 2O 3 and Y 2O 3 at sintering temperatures. SEM observation revealed that SiC exhibited a uniformly distributed fine-grained microstructure and a highly intergranular fracture behavior. The maximum values of strength and toughness were up to 625 MPa and 7.5 MPa m 1/2, respectively. The improved toughness is considered to be mainly associated with the deflection of cracks along interphase boundaries due to a weak interface as well as with the introduction of microcracks at the interface between SiC grains and the secondary phases due to a residual tensile stress from thermal expansion mismatch.