Relationship between Microstructure and Fracture Toughness of Toughened Silicon Carbide Ceramics

Abstract

Different microstructures in SiC ceramics containing Al 2 O 3 , Y 2 O 3 , and CaO as sintering additives were prepared by hot-pressing and subsequent annealing. The microstructures obtained were analyzed by image analysis. Crack deflection was frequently observed as the toughening mechanism in samples having elongated ␣-SiC grains with aspect ratio >4, length >2 m, and grain thickness (t) <3 m (defined as key grains 1). Crack bridging was the dominant toughening mechanism observed in samples having grains with thickness of 1 m < t < 3 m and length >2 m (key grains 2). The values of fracture toughness varied from 5.4 to 8.7 MPa⅐m 1/2 with respect to microstructural characteristics, characterized by mean grain thickness, mean aspect ratio, and total volume fraction of key grains. The difference in fracture toughness was mainly attributed to the amount of key grains participating in the toughening processes.

Sinterability of Nano-Sized Silicon Carbide Powders

“…was obtained when we used the submicron powder with Al 2 O 3 -Y 2 O 3 -CaO as a sintering additive and hot-pressed the powder mixture at 1800c C for 1 h under a pressure of 25 MPa. 16 Thus, the poor sinterability of the commercial nanosized SiC powders may be related to the difference in the amounts of impurities. Figure 3 shows the effect of the free carbon content on the sintered density of the nano-sized SiC powders.…”

“…The AYC mixture was selected as a sintering additive, because of its potential to lower the sintering temperature further than that afforded by the typical Al 2 O 3 -Y 2 O 3 composition, 15 as well as its potential to improve the toughness. 16 2. Experimental procedure Three kinds of commercially available nano-sized SiC powders see Table 1 and a treated nano-sized SiC powder were used.…”

Toughening Mechanisms in SiC-TiC Composites

“…The grains interacting with a propagating crack were quantitatively analyzed by image analysis (Image-Pro Plus, Media Cybernetics, Maryland, U.S.A.), according to a procedure shown in a previous study. 8) De®nitions of microstructural characteristics are demonstrated in Ref. 8.…”

“…8) De®nitions of microstructural characteristics are demonstrated in Ref. 8. The thickness (t) of each grain was determined directly from the shortest grain dimension in its two-dimensional image; the apparent length (l) of each grain was obtained from the longest dimension.…”

Effect of additive composition on mechanical properties of pressureless sintered silicon carbide ceramics sintered with alumina, aluminum nitride and yttria

“…Therefore, SiC ceramics have been extensively used in many industrial applications such as wear parts, diesel particulate filters, membranes, optical mirrors, various parts for semiconductor processing, and armor plates, and are potential candidates for nuclear fuel capsules and fusion reactor parts. Interest in liquid-phase sintered SiC (LPS-SiC) has grown continually over recent years because such a material is easier to process and has superior mechanical and electrical properties as compared to solid-state sintered SiC [11][12][13][14][15].…”