Carbon-fiber composites with metal matrices

Figure 1. Evans diagram for estimating the galvanic current density. The bimetallic electrode consists of a carbon fibre embedded in a 6061 aluminium alloy (metal matrix composites). Two galvanic regimes can be reached as function of the aeration of the corrosive media. This analysis does not take into account the spatial distribution of the carbon fibers in the metallic matrix (see Fig. 12). Reprinted with permission from/nrernahono/Mafen-alsReviews, 39 (1994) 245.Copyright 1994 Maney Publishing. ...

Goldie W, Metallic Coating of Plastics, Vol 1, Electrochemical Publications Ltd, Middlesex, 1968. Abraham S, Pai BC, Satyanarayana KG, Vaidyan VK, Copper coating on carbon fibers and their composites with aluminum matrix, J Mater Sci, 27, 3479-3486, 1992. 

Balaba WM, Weirauch DA, Perrotta AJ, Armstrong GH, Anyalebechi PN, Kauffman S, MacInnes AN, Winner AM, Barron AR, Effect of sUoxane spin-on-glass and reaction bonded silicon oxycarbide coatings with a self-propagating interfacial reaction treatment (aspire) in the synthesis of carbon/graphite fiber-reinforced A1 metal matrix composites, J Mater Res, 8(12), 3192-3201, 1993. 

Composites are usually classified by the type of material used for the matrix. The four primary categories of composites are polymer matrix composites (PMCs), metal matrix composites (MMCs), ceramic matrix composites (CMCs), and carbon matrix composites (CAMCs). The last category, CAMCs, includes carbon/carbon composites (CCCs), which consist of carbon matrices reinforced with carbon fibers. For decades, CCCs were the only significant type of CAMC. However, there are now other types of composites utilizing a carbon matrix. Notable among these is silicon carbide fiber-reinforced carbon, which is being used in military aircraft gas turbine engine components. 

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... 

Metal coating has been used to produce metal matrix [12, 13] or polymer matrix [11, 14-18] composites or reinforced with carbon fibers. In the case of electroless coating, carbon fiber surfaces are metallized when exposed to coating solutions containing a metal salt in the presence of a reductant. Once the first layer was formed it acts as a catalyst for the process. 

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). 

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]. 

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. 

Ceramic reinforcing fibers are utilized both in a continuous form (endless fibers) and in a discontinuous form (e.g. whiskers, short fibers). Most of the continuous fibers are utilized in the manufacture of composites with polymer matrices (PMC), where they are in competition with other high performance fibers (boron, carbon fibers), mainly for military or aerospace applications. Discontinuous fibers are generally used for the manufacture of metal matrix (MMC) and ceramic matrix (CMC) composites. 

Besides these developments, which are directed at specific applications, NijAl alloys are used for the development of inter-metallic matrix composites which contain reinforcing particles or fibers of borides, carbides, oxides or carbon (Fuchs, 1989 Lee et al., 1990 Tortorelli et al., 1990 Al-man and Stoloff, 1991 Kumar, 1991 McKamey and Carmichael, 1991 Muk-herjee and Khanra, 1991 Brennan etal., 1992). Apart from the mechanical properties and the necessary corrosion resistance, the chemical compatibility of the used phases is of primary importance with respect to the long-term stability. It was found that SiC, B4C, and TiBj react extensively with Nij Al alloys, whereas very little reaction has been observed with AljOj or Tie in NijAl (Fuchs, 1989 Lee etal., 1990 Brennan etal., 1992). It should be noted that NijAl alloys are used not only as the matrix material, but also as a reinforcing phase in, e.g. an Al alloy to form a metal-matrix composite (Metelnick and Varin, 1991). 

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