Whisker-reinforced ceramic composites high-toughness

Whisker-reinforced ceramic composites have come into prominence for structural applications because of their potential for high strength and fracture toughness which can be retained at elevated temperatures. Originally applied... 

As a class of ceramic materials, SiC whisker-reinforced ceramic composites were developed for potential structural applications because of the significant improvements in the mechanical properties these materials offered as compared to the monolithic materials. The incorporation of SiC whiskers into alumina ceramics resulted in increases in strength, fracture toughness, thermal conductivity, thermal shock resistance and high temperature creep resistance. These discoveries initiated several years of intense study into this class of composites. 

It is well established that improvements in the room-temperature fracture toughness of ceramics can be achieved by whisker reinforcement, and various mechanisms have been proposed to explain the phenomenon. Recently, two studies have examined the fracture behavior of SiC whisker-reinforced alumina composites at high temperatures to determine the dependence of fracture toughness on temperature, the effect of test atmosphere on fracture toughness, and mechanisms of fracture.33,34 In both studies, single-edged-notched bars... 

Ceramic matrix composites are candidate materials for high temperature stmctural appHcations. Ceramic matrices with properties of high strength, hardness, and thermal and chemical stabiUty coupled with low density are reinforced with ceramic second phases that impart the high toughness and damage tolerance which is required of such stmctural materials. The varieties of reinforcements include particles, platelets, whiskers and continuous fibers. Placement of reinforcements within the matrix determines the isotropy of the composite properties. 

The ideal SiC whisker for reinforcement of ceramic composites would have several characteristics that would also depend on the matrix phase. In every case, the ideal whisker would have no internal structural imperfections, be relatively smooth and possess high strength. For alumina matrices where the difference in thermal expansion is great between the matrix and the whisker, the whisker diameter would be in the range of 1.5-2.0 p.m [9]. For alumina-SiC composites, it was determined that the presence of excess surface carbon on the whiskers resulted in a weak interfacial bond and produced materials with high toughness and strength [9]. 

Other ceramic cutting-tool materials include alumina, Si-Al-0-N, alumina-carbide composites and, more recently, a composite of silicon nitride reinforced with silicon carbide whiskers. This last material can be produced by chemical-vapor infiltration (CVI) and has high strength and toughness as shown in Table 18.3.Cl... 

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