Numerical Modeling of Fiber-Reinforced Metal Matrix Composite Processing by the Liquid Route: Literature Contribution
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LIQUID route processing is the most promising technology for manufacturing fiber-reinforced metal matrix composites (MMCs) both in terms of cost and the mass production of composite parts. Impregnation of the fibrous preform via the liquid route consists of injecting the metal in a liquid state into a mold containing the fibers. The principle may be simple, but with only a few very specific exceptions,[1] it comes up against problems related to the wetting of the mineral fibers by the liquid metal.[2] To ensure that impregnation is carried out successfully, either the wetting process can be improved or the pressures used must be sufficiently high to force the metal to penetrate. There are several solutions to the first case: the addition of chemical elements to the matrix to reduce the surface tension of the liquid metal or the application of a pretreatment to the fibers. For example, the fibers can be coated with ceramic or metal deposits. Metallic coatings mainly of nickel or copper are used to improve the wettability of fibers by aluminum.[3,4] These coatings can be obtained through electrolytic methods, with current, or by
ERIC LACOSTE, CORINNE ARVIEU, and OLIVIER MANTAUX are with the University of Bordeaux, I2M CNRS, Site IUT, 15, rue Naudet - CS 10207, 33175, Gradignan Cedex, France. Contact e-mail: [email protected] Manuscript submitted May 8, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
electroless techniques.[5,6] Other techniques consist of the chemical activation of wetting by fluoride treatments with K2ZrF6[7] or K2TiF6.[8] After improving the wetting, the fibrous preform can then be impregnated by gravity casting or by exerting a low pressure directly with the aid of a piston or a pressurized inert gas (Figure 1). These techniques generate additional costs, however (time, pollution), and leave residual impurities in the final product. Another technique is to carry out medium pressure die casting: after creating a vacuum in the different parts of the system (mold and preform), the preform and the metal are preheated; gas pressure of around 10 MPa is then applied to the metal to introduce it into the mold and penetrate the preform. Using low pressures has the advantage of not damaging the fibrous preform during processing; however, it generates slow cooling rates that favor chemical reactions between the matrix and the reinforcement. The chemical interaction between the fibers and the matrix causes interfacial zones to form, which may affect the characteristics of the composite, as can be seen, for example, in the case of titanium MMCs.[9] The use of high pressures (of around 100 MPa) is interesting in several respects, mainly because it is then possible to overcome problems related to wetting (Figure 2), to limit chemical interactions between the fibers and the metal, and also to minimize the formation of microporosities during impregnation. All the techniques used to produce MMCs by infiltration of a fibrous preform have been described and compared by Sree Manu et al. in a recent bibliographic article.
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