Crack propagation and interfacial property in SiC-AI_2O_3-Y_2O_3 ceramic

摘要

The successful development of AI2O3 and Y2O3 as sintering aids by Oraori et cil. [1] involving the densification of SiC ceramics via a pressureless sintering route opens up the feasibility for structural applications. The densification of SiC-Al2O3-Y2O3 is based on a liquid-phase sintering mechanism by which the secondary phases, i.e. alumina and yttria, together with a small quantity of SiC>2 phase originating from the starting SiC powders, form eutectic melt at temperatures below ~2000 °C. One of the prominent characteristics of the mechanical properties of SiC ceramics is the significant improvement of fracture toughness, to a value of as high as 8.3 MPam0'5 [2], which is considered to be a result of the formation of elongated grains, and is comparable with silicon nitride ceramic [2,3]. Recently, Lee et al. [2] indicated that a significant improvement of fracture toughness can be achieved only by using B-SiC as starting powder. (5 =E> a phase transformation causes the formation of elongated grains, whereas using a-SiC as starting powder gives grain coarsening which increases the fracture toughness only slightly. In a previous study [5], an attempt at using a and B-SiC mixtures as starting powder was made and the sintered SiC ceramic obtained showed considerable improvement in fracture toughness and mechanical strength compared to those reported in literature. Furthermore, it also showed that the high-temperature strength at 1200 °C preserves up to 90% of room-temperature strength [6].