Fiber-reinforced directed metal oxidation composites

Lanxide A process for making composites of metals with oxides. A molten metal reacts with an adjacent oxidant and is progressively drawn through its own oxidation product so as to yield a ceramic-metal composite. Fibers or other reinforcing materials can be placed in the path of the oxidation reaction and so be incorporated into the final product. The Lanxide Corporation was founded in 1983 in Newark, DE, to exploit this invention. In 1990 it formed a joint venture with DuPont to make electronic components by this process. Variations are Dimox (directed metal oxidation), for making ceramic metal composites, and Primex (pressureless infiltration by metal), for making metal matrix composites. 

Fig. 14. Micrograph of a C-fiber reinforced Si3N4 matrix composite prepared by directed metal oxidation. From Johnson [52],...

A variety of CMC systems have been developed and fabricated in the past. These have included aluminum oxide, aluminum nitride and sihcon nitride matrix composites [3-5]. The reinforcement has predominantly consisted of silicon carbide based fibers. Oxide based fibers have also been evaluated over the years as and when they have become available. This chapter reviews the development effort of silicon carbide reinforced aluminum oxide matrix composites fabricated via directed metal oxidation and compares them with those reinforced with oxide fibers. 

The generic process for fabrication of fiber-reinforced aluminum oxide matrix composites by directed metal oxidation includes preforming, fiber-matrix interface coating, matrix growth and removal of residual aluminum. A flow chart with the various processing steps is shown in Fig, 1. 

A.S. Fareed, Ceramic Matrix Composite Fabrication and Processing Directed Metal Oxidation, Handbook on Continuous Fiber Reinforced Ceramic Matrix Composites, ed. R.L. Lehman, S.K. El-Rahaiby Jr and J.B. Wachtman, Jr., ClAC/ACers, 301-324 (1995). 

G.H. Schiroky, A.S. Fareed, B. Sonuparlak, C.T. Lee, and B. Sorenson, Fabrication and Properties of Fiber-Reinforced Ceramic Composites Made by Directed Metal Oxidation, pp. 151-163, in Flight-Vehicle Materials, Structures and Dynamics - Assessment and Future Directions, Vol. 3, S.R. Levine Jr, ed, ASME, New York, 1992. 

Farced, A. S., Schiroky, G. H., and Kennedy, C. R. (1993). Development of BN/SiC duplex fiber coatings for fiber-reinforced aluminia matrix composites fabricated by directed metal oxidation. Ceram. Eng. Sci. Proc. 18 794-801. 

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). 

One approach for fabricating fiber reinforced ceramic matrix composites is the directed oxidation of metals, a process first introduced by Lanxide Corporation [1, 2] and later used successfully to produce turbine engine and aerospace components. Rights to the DIMOX technology, as it was identified, were ultimately acquired by Power Systems Composites, L.L.C., a subsidiary of the Power Systems business of the General Electric Company. 

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. 

New types of ceramic composites with high thermal shock resistance have recently been developed that show some promise for gas turbine applications. These composites consist of a ceramic matrix reinforced by ceramic fibers or platelets inside the matrix. The fibers pull out of the matrix during fracture to resist crack propagation. Such composites can be readily fabricated using a new process developed by Lanxide Corporation [18]. The process uses directed oxidation reactions of molten metals to grow a ceramic matrix around a reinforcing material. 

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