Ceramic composites fracture toughness

The first CMCs to be developed consisted of three major components a ceramic matrix, fibers embedded in the matrix, and a tailored interface between the fiber and the matrix. Although these materials show damage tolerance and non-brittle behavior, the non-oxide materials that compose the CMCs are prone to oxidation, especially when matrix cracks are present. Lately, the development of an all-oxide CMC has captured the researchers attention. In these oxide/oxide composites, fracture toughness is achieved through crack deflection inside the matrix. A controlled level of matrix porosity will provide suitable conditions for crack deflection while inherently impeding oxidation during high temperature service. ... 

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. 

Ceramic-matrix fiber composites, 26 775 Ceramics mechanical properties, 5 613-638 cyclic fatigue, 5 633-634 elastic behavior, 5 613-615 fracture analysis, 5 634-635 fracture toughness, 5 619-623 hardness, 5 626-628 impact and erosion, 5 630 plasticity, 5 623-626 strength, 5 615-619 subcritical crack growth, 5 628—630 thermal stress and thermal shock, 5 632-633... 

Such ceramic fibers offer uniquely strong and resistant inexpensive materials including new ceramic composites that have great fracture toughness. 

Composites provide an atPactive alternative to the various metal-, polymer- and ceramic-based biomaterials, which all have some mismatch with natural bone properties. A comparison of modulus and fracture toughness values for natural bone provide a basis for the approximate mechanical compatibility required for arUficial bone in an exact structural replacement, or to stabilize a bone-implant interface. A precise matching requires a comparison of all the elastic stiffness coefficients (see the generalized Hooke s Law in Section 5.4.3.1). From Table 5.15 it can be seen that a possible approach to the development of a mechanically compatible artificial bone material... 

By infiltrating molten metals and alloys into porous ceramics you can make materials with a higher fracture toughness than that of the ceramic material itself. In addition these materials possess the conducting properties of metals. A combination of certain materials which results in a set of properties which the individual materials do not possess is called a composite. The entire chapter 14 is devoted to these materials. During and after the mentioned infiltration an exchange reaction can take place, e.g. 

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