Fracture toughness ceramic-matrix composites

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Chlup, Z., Dlouhy, I., Boccaccini, A.R. (2001), Fracture toughness of thermally shocked SiC-fibre reinforced glass matrix composite , in Krenkel, W., Naslain, R., Schneider, H. (editors), High Temperature Ceramic Matrix Composites, Wiley, 463-468. 

Silicon carbide has attracted considerable interest because of its good mechanical and physical properties and chemical inertness. One of the most important applications of SiC is to produce a matrix reinforced by fibres, forming ceramic-matrix composites. These composite materials exhibit much better fracture toughness than monolithic ceramics. Compared with carbon/carbon composites, fibre-reinforced SiC matrix composites possess superior oxidation resistance and mechanical properties. The Si-C-H-Cl system (e.g. methyltrichlorosilane, CH3SiCl3) has been used for SiC deposition because it is easy to produce stoichiometric SiC deposits. 

These fibers have high tensile strength and heat resistance. In recent years, SiC fibers or their fabrics have been used to prepare fiber-reinforced ceramic-matrix composites. Such composites have high strength and high fracture toughness, even at elevated temperatures [5,6], and are a promising class of... 

TABLE 2. Overview of fibre-reinforced glass and glass-ceramic matrix composites (a ultimate fracture strength, fracture toughness, 2-D 2 dimensional reinforcement) [6]... 

Becher, P. F., Heueh, C., Angellita, P., and Tiegs, T. N. (1988). Toughening behavior in whisker-reinforced ceramic matrix composites. / Am. Ceram Soc. 71 1051-1061. Homeny,J., Vaughn, W. L., and Ferber, M. K. (1990). Silicon carbide whisker/alumina matrix composites effect of whisker surface treatment on fracture toughness./ Am Ceram. Soc. 73 394-402. 

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