Processing and creep characterization of a model metal matrix composite: Lead reinforced with nickel fibers
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I.
INTRODUCTION
M E T A L matrix composites have generated considerable interest in recent years for potential applications in automobile engines, airframe structural members, and gas turbine engines. The primary advantage of composites over bulk metals and alloys is their increased specific strength and specific modulus and the retention of those mechanical properties at high temperatures. While the room-temperature properties of metal matrix composites have been studied extensively, an understanding of the high-temperature deformation behavior of composites under creep conditions is still lacking. Consequently, there is a need for high-temperature mechanical test data and deformation analyses on model metal matrix composite systems. In this study, the steady-state creep properties of a nickel-fiber reinforced lead matrix composite are characterized. Lead was chosen as a matrix material in this model system because of its low melting point which results in relatively fast creep tests at low temperatures. The creep behavior of pure lead has been studied extensively, and the work of Kelly and Street on the creep of lead reinforced with bronze fibers provides a point of comparison for the composite creep results, u.2~ In addition, lead forms a wide range of solid solutions with other low melting point metals, such as indium, so that the effect of matrix solid solution alloying on the creep of the composite may be easily studied in future investigations. Nickel fibers were chosen as the reinforcing material because of their availability in thin wire form and their thermodynamic stability with respect to the lead matrix. Some studies have even shown that lead composites might have practical applications as electrodes in high energy density storage batteries. [3]
T.L. DRAGONE, Graduate Research Assistant, and W.D. NIX, The Lee Otterson Professor of Engineering, are with the Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305-2205. J.J. SCHLAUTMANN is with the Materials Science Department, San Jose State University, San Jose, CA 95192. Manuscript submitted October 16, t990. METALLURGICAL TRANSACTIONS A
II.
PROCESSING
Lead-nickel composites were processed using a foil metallurgy technique illustrated in Figure 1. Commercial grade 6.35 mm thick lead plate was rolled to approximately 0.18 mm thick foils. This was done in a series of 15 steps in order to limit the deformation in any one reduction pass and, thereby, reduce the tendency for cracking and tearing of the foils. After rolling, the foils were cut into 6.35 x 12.7 cm pieces and were cleaned using an acetic/nitric acid solution. Cut nickel wire fibers with a diameter of 0.125 mm and a length of 2 mm (aspect ratio = 16) were provided by Goodfellow Metals and Materials, Malvem, PA. The proprietary process used to cut the fibers resulted in extremely good control of fiber length, with a standard deviation in length of less than 0.02 mm. Fibers were loaded onto the lead foils to a density of approximately 25 to 30 fibers/cm 2. T
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