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

SiC powders were pressureless sintered to about 98% of the theoretical density by using 10 wt.% (Al2O3 + Y2O3) as sintering additives. The densification mechanism was attributed to liquid-phase sintering due to the formation of a eutectic liquid between Al2O3 and Y2O3 at sintering temperatures. SEM observation revealed that SiC exhibited a uniformly distributed fine-gained 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. (C) 1999 Elsevier Science S.A. All rights reserved.