METAL-MATRIX, CARBON-FIBER COMPOSITES

The diffusion problems can be partially overcome by applying a barrier coating such as titanium, boron, nickel, copper, or niobium carbide over the fiber priorto processing the composite. The latter material, NbC, has shown excellent diffusion-barrier characteristics in a laminate composed of P-100 fibers (43 vol.%) and a copper matrix.P f A cross-section of the composite after isothermal exposure at 815°C for 240 hours is shown in Fig. 9.6. 

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Low cost PM route for titanium matrix carbon fiber composites. Powder Metall, 39(2), 97 99, 1996. 

BPA/DC-based composition served as a polymer matrix in carbon fiber composites [24]. Metal powder or fiber filled molding compounds were also described. The molding compounds, which can contain, moreover, numerous other components, bismaleimides (cf. Sect. 5) in particular, are used for the manufacturing of heat conductive molds for injection molding [25],... 

The effectiveness of using the thermal input for EB crosslinking of carbon-fiber composite matrix materials to reduce dose was shown by M. Lavalle. Proper combinations of monomer, sulfur and metals subjected to ionizing radiation were found to produce nano-particles that could be of use in electronic applications. 

D. Lewis, R.W. Rice, Further Assessment of Ceramic Fiber Coating Effects on Ceramic Fiber Composites, NASA Conf. on Metal Matrix, Carbon, and Ceramic Matrix Composites, (Ed. J. D. Buckley), Cocoa Beach, FL, 1985. 

Composites may be identified and classified many hundreds of ways. There are aggregate-cement matrix (concrete), aluminum film-plastic matrix, asbestos fiber-concrete matrix, carbon-carbon matrix, carbon fiber-carbon matrix, cellulose fiber-lignin/silicic matrix, ceramic fiber-matrix ceramic (CMC), ceramic fiber-metal matrix, ceramic-metal matrix (cermet), concrete-plastic matrix, fibrous-ceramic matrix, fibrous-metal matrix, fibrous-plastic matrix, flexible reinforced plastic, glass ceramic-amorphous glass matrix, laminar-layers of different metals, laminar-layer of glass-plastic (safety glass), laminar-layer of reinforced plastic, laminar-layers of unreinforced plastic. 

R Y. Leung, S. T. Gonczy, G. T. Stanford, C. E. Southern, D. M. Lipkin, Near-Net Shape Formability and Fibrous Fracture in Glass Matrix Composites Reinforced with Continuous Ceramic Fibers, NASA Conference Publication 3097, Proceedings ofthe 14th Conference on Metal Matrix, Carbon, and Ceramic Matrix... 

Conductive materials in fibrillar shape may be advantageous compared to films due to their inherent properties such as anisotropy, high surface area, and mechanical strength. Fibrous conductive materials are of particular interest in electroactive composites. Fine metal nanoparticles, carbon fibers, and carbon nanotubes have been efficiently distributed in an insulating polymer matrix in order to improve both electrical and mechanical properties. 

Denison P, Jones FR, Brown A, Humphrey P, Paul AJ, Scanning SIMS spectography of cfrp, Ishida H ed., Interfaces in Polymer, Geramic and Metal Matrix Gomposites, 239-248, 1988. Hearn MJ, Briggs D, ToF-SIMS studies of carbon fiber surfaces and carbon fiber composite fracture surfaces. Surface Interface Analysis, 17(7), 421 et seq, 1991. 

In Malaysia, an Australian company, Talon, manufactures elegant, durable and weatherproof ultra lightweight tables and chairs from metallic coated carbon fiber incorporated in an epoxy matrix. Composite Design (Australia) also manufactures a range of lightweight furniture from cfrp. 

The matrix of carbon-fiber composites can be a polymer (resin), a ceramic, a metal, or carbon itself (carbon-carbon). These matrix materials are described in Secs. 3.0, 4.0 and 5.0 below. 

Oxides such as alumina (AI2O3) are generally not suitable matrix materials in carbon-fiber composites as the carbon reduces the oxide to form metal carbide and CO during the fabrication process. The oxidation of the carbon fiber may be sufficient to generate a high partial pressure of CO which results in the formation of gas bubbles and cracks in the oxide.l ... 

Carbon itself has been successfully used as a biomaterial. Carbon based fibers used in composites are known to be inert in aqueous (even seawater) environments, however they do not have a track record in the biomaterials setting. In vitro studies by Kovacs [1993] disclose substantial electrochemical activity of carbon fiber composites in an aqueous environment. If such composites are placed near a metallic implant, galvanic corrosion is a possibiHty. Composite materials with a polymer matrix absorb water when placed in a hydrated environment such as the body. Moisture acts as a plasticizer of the matrix and shifts the glass transition temperature towards lower values [Delasi and Whiteside, 1978], hence a reduction in stifihess and an increase in mechanical damping. Water immersion of a graphite epoxy... 

As mentioned in 10.2.3, super-strong polymeric, ceramic, metallic, and carbon fibers are now used to reinforce various t) es of composifes. However strong the fiber may be, fhe composite is no better than the bond between the fiber and its matrix. Consider a fiber of diameter D and length L, half of which is imbedded in a matrix along the z-axis. If a longitudinal force F is applied that tries to pull the fiber ouf of the matrix, the matrix will... 

Electronic-Grade MMCs. Metal-matrix composites can be tailored to have optimal thermal and physical properties to meet requirements of electronic packaging systems, eg, cotes, substrates, carriers, and housings. A controUed thermal expansion space tmss, ie, one having a high precision dimensional tolerance in space environment, was developed from a carbon fiber (pitch-based)/Al composite. Continuous boron fiber-reinforced aluminum composites made by diffusion bonding have been used as heat sinks in chip carrier multilayer boards. 

Sihcon carbide fibers exhibit high temperature stabiUty and, therefore, find use as reinforcements in certain metal matrix composites (24). SiUcon fibers have also been considered for use with high temperature polymeric matrices, such as phenoHc resins, capable of operating at temperatures up to 300°C. Sihcon carbide fibers can be made in a number of ways, for example, by vapor deposition on carbon fibers. The fibers manufactured in this way have large diameters (up to 150 P-m), and relatively high Young s modulus and tensile strength, typically as much as 430 GPa (6.2 x 10 psi) and 3.5 GPa (507,500 psi), respectively (24,34) (see Refractory fibers). 

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

Shear-stress-shear-strain curves typical of fiber-reinforced epoxy resins are quite nonlinear, but all other stress-strain curves are essentially linear. Hahn and Tsai [6-48] analyzed lamina behavior with this nonlinear deformation behavior. Hahn [6-49] extended the analysis to laminate behavior. Inelastic effects in micromechanics analyses were examined by Adams [6-50]. Jones and Morgan [6-51] developed an approach to treat nonlinearities in all stress-strain curves for a lamina of a metal-matrix or carbon-carbon composite material. Morgan and Jones extended the lamina analysis to laminate deformation analysis [6-52] and then to buckling of laminated plates [6-53]. 

Diwanji, A.P. and Hall, I.M. (1992). Fiber and fiber-surface treatment effects in carbon-aluminum metal matrix composites. J. Mater. Sci. 27, 2093-2100. 

Donnet, J.B., Dong, S, Guilman, G., Brcndle, M. (1988). Carbon fibers electrochemical and plasma surface treatment. In Proc. ICCl-U, Interfaces in Polymer. Ceramic and Metal Matrix Composites (H. Ishida cd.), Elsevier Sci. Pub., New York, pp. 35-42. 

Dieffendorf, R. J. (1985). Comparison of the various new high modulus fibers for reinforcement of advanced composites with polymers, metals and ceramics as matrix, pp. 46-61. In Fitzer, E. ed. Carbon Fibers and Their Composites, Springer-Verlag, New York. 

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