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Nickel is deposited over pristine, surface-treated, and brominated P-100 carbon fibers using cementation and electroplating techniques. The fibers are brominated by bromine vapor for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment is performed by etching fibers electrochemically in a dilute sodium electrolyte for 3 min or by immersing fibers in nitric acid for 72 h. Electroplated-coated fibers show better tensile properties than cementation-coated fibers. Tin-lead alloy composites reinforced by nickel-coated fibers (which are pristine, anodically oxidized, and brominated) are fabricated by squeeze casting. The composites containing coated carbon fibers with bromination or surface treatment have higher tensile and shear strength than the ones containing coated pristine carbon fibers. In addition, the composite containing coated carbon fibers with bromination shows the best performance in the tensile properties.

I. INTRODUCTION The white metal, babbit metal, or bearing metal, based on lead or tin, has excellent frictional properties. It also possess a number of other important properties such as embeddability, conformability, and corrosion resistance. However, bearing metals are mechanically weak. Tin-lead alloys are most commonly used for solders and bearings. Solder preforms are used to join various parts of electronic packages. Because the thermal expansion coefficient of a solder is in general much higher than that of the substrate, the solder joint often suffers from poor resistance to thermal fatigue. Thus, there is a need for a solder with a low thermal expansion. If tin-lead alloys can be made stronger, they may also bear greater loads and hence offer the possibility of reduction in overall bearing size for a given application. Composite materials can be tailored to exhibit a chosen thermal expansion coefficient, when the filler species and the filler volume fraction can be chosen. For a low thermal expansion composite, the filler must have a low thermal expansion coefficient. Moreover, the filler is preferably a good electrical conductor because the soldered joint may serve as electrical connection as well as mechanical connection. It is also preferably a good thermal conductor for heat dissipation from the electronic package. In addition, the filler should have good mechanical properties in order to strengthen the tin-lead alloy. One of the suggested means of strengthening bearing involves the incorporation of carbon fibers, thus using the fibers as a reinforcing agent and possibly also as a lubricating agent by virtue of its graphic nature. In addition to their nearly zero thermal expansion coefficient, carbon fibers are widely available in a con1730 http://journals.cambridge.org

J. Mater. Res., Vol. 10, No. 7, Jul 1995 Downloaded: 14 Mar 2015

tinuous form, which makes them more effective for lowering the thermal expansion coefficient of the composite, and prevents the fiber distribution from becoming nonuniform after remelting and solidification.2 Carbon fiber-reinforce