A method for fabrication of aluminum-alumina composites
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INTRODUCTION
M E T A L matrix composites containing a variety of high strength, high modulus fibers are receiving considerable emphasis in advanced materials requirements. Potential applications are those which can take advantage of the excellent strength-to-density and stiffness-to-density ratios of the composite materials. In the aluminum alloy matrix composites area, applications are envisioned in large lightweight structures in the aerospace, transportation, communication, and manufacturing industries. It is generally agreed that alumina fiber is an ideal reinforcing material for aluminum and its alloys, since the metal and fibers are physically and chemically compatible at the projected service temperature of the resultant composites. However, produCtion of the composites of the two materials is limited by the inability of the liquid metal to wet the fibers. A new method for the fabrication of A1/A1203 composites which involves the addition of discontinuous fibers into a fully liquid aluminum alloy is described in this paper. Complete wetting and bond formation were readily achieved and resulted in enhanced mechanical properties over those of the matrix alloy. The fabrication of fiber reinforced composites involves the combination of the matrix with the reinforcing fiber. The methods used can be classified into deposition, solid state, and liquid processes. 1Up to the present, liquid filtration has been the most successful for the production of laboratory quantities of aluminum alloy-alumina fiber composites.25 A limitation of this technique is the inability of the liquid metal to wet the fibers without the addition of a wetting agent such as lithium. For wetting to occur, the contact angle, 0, must be less than 90 deg. For contact angles 0 > 90 deg, the capillarity effects require an external pressure in order that the liquid alloy will infiltrate the fiber bundles. 6 However, even the application of pressure does not completely solve the problem, since shrinkage during solidification may be enough to cause debonding or void formation in the channels between the fibers. B.F. QUIGLEY is with the Technical Staff, Metallic Materials Branch, Naval Surface Weapons Center, White Oak, MD. G.J. ABBASCHIAN is Associate Professor, Department of Materials Science and Engineering, University of Florida, Gainesville, FL. R. WUNDERLIN is Manager of Quality Assurance at SWA, Altenrhein, Switzerland, and R. MEHRABIAN is Chief of the Metallurgy Division, National Bureau of Standards, Building 223, Room B266, Washington, DC, and Adjunct Professor of Metallurgy, University of Illinois, Urbana, IL. Manuscript submitted April 21, 1981. METALLURGICAL TRANSACTIONS A
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A number of studies of contact angle as a function of temperature in the A1/A1203 system have previously been reviewed. 1The results indicate that temperatures well above the melting point of aluminum would be necessary to promote wetting (099 pct) and is chemically inert and highly stable at elevated temperatures. 9 Its properties are given in Table 1. The fil
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