Ceramic composites whisker reinforcement

II. Whiskers and Ceramic Matrix Whisker-Reinforced Composites. 160... 

Presently the 2 sources of AI2O3, 3 sources of SijN,-, and 2 sources of Y2O3 powders used for processing both AI2O3 and SijN matrix composites are being analyzed for their flocculation/dispersion behavior as functions of pH, time and temperature. The results of this task should be of benefit to processing of monolithic ceramics, self-reinforcing ceramics, and whisker reinforced ceramics. 

Nonpowder Synthesis. Many ceramic composites (qv) under iavestigation utilize reinforcing ceramic whiskers or fibers to achieve toughening (19). Whiskers (17,19,20) are produced by vapor-synthesis techniques. SiC whiskers can be produced by the rice hull or vapor—soHd (VS) method whereby rice hulls are pyrolyzed to produce a mixture of carbon, C, and Si02, and whiskers are produced by directional growth by vapor... 

Table 4. Whisker Reinforcements for Ceramic-Matrix Composites...

Ceramic composites, which use ceramic fiber or whisker reinforcement in a ceramic matrix, are less susceptible to brittle failure since the reinforcement intercepts, deflects and slows crack propagation. At the same time, the load is transferred from the matrix to the fibers to be distributed more uniformly. These ceramic composites are characterized by low density, generally good thermal stability, and corrosion resistance. 

Whipple s rules, 20 138 Whisker reinforcement, 5 554, 555, 654 performance in ceramic—matrix composites, 5 572-575 physical properties, 5 557t synthesis, 5 642-643 and toughening, 5 622 Whiskers, silicon carbide, 22 533-534 White... 

Fibre-whisker- and particulate-reinforced ceramic composites... 

Schematic representation of cracking in (a) a monolithic ceramic and (b) a ceramic composite reinforced with whiskers (a- > a2) ... 

Jia, D.C., Zhou, Y. and Lei, T.C. Thermal shock resistance of SiC whiskers reinforced Si3N4 ceramic composites , Ceramics International, 22 (1996) 107-112. 

Chu, C.Y., Singh, J.P. and Routbort, J.L. High-temperature failure mechanisms of hot-pressed Si3N4 and Si3N4/Si3N4-whisker-reinforced composites , J. Am. Ceram. Soc., 76[5] (1993) 1349-1353. 

Chu, C.Y. and Singh, J.P. Mechanical properties and micro structure of Si3N4-whisker-reinforced Si3N4 matrix composites , Ceram. Eng. Sci. Proc., 11 [7—8] (1990) 709-720. 

Desmarres, J.M., Goursat, P, Besson, J.L. Lespade, P. and Capdepuy, B. SiC whiskers reinforced Si3N4 matrix composites Oxidation behavior and mechanical properties , J. Eur. Ceram. Soc., 7 (1991) 101-108. 

Whisker-reinforced glass-ceramic matrices are expected to find several applications in automotive components, metal forming, cutting tools, etc., due to their low thermal expansion, high thermal shock resistance, high reliability and low material and processing costs. Some industrial applications for continuous fibre-reinforced ceramic matrix composites (CMCs) are listed below. 

Unlike fibre- or whisker-reinforced composites, particulate composites have the advantage of being compatible with conventional powder processing, and in many cases can be pressurelessly sintered. As with other ceramic microstructures, a myriad of other ingenious fabrication routes have also been reported, but these are too numerous and system-specific to describe here. This section merely outlines the main points of powder processing where the production of composites in chemically compatible systems (i.e. those in which the components do not react chemically with one another) differs from that of monolithic ceramics. 

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