Infiltration of fibrous preforms by a pure metal: Part II. Experiment
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I.
INTRODUCTION
IN a
previous paper, m analytical solutions were given to describe the unidirectional infiltration of a pure metal into a preform of aligned fibers under the application of a constant pressure. In particular, the influence on infiltration kinetics was shown for the processing parameters, including (a) fiber volume fraction, (b) fiber temperature, (c) metal superheat, and (d) applied pressure. Flow of metal into a fiber preform heated significantly below the metal melting point was shown to result in the solidification of metal around the fibers to form a sheath. Also, it was shown that the effect of metal superheat was to remelt this solid metal sheath at a remelting front separating two regions in the composite. The cessation of fluid flow was shown to be due to solidification from the mold wall progressing inward and closing the flow channel. Calculations were performed to predict the behavior of pure aluminum infiltrating alumina fibers in cross flow under a variety of experimental conditions. In this paper, experiments are presented to test the resuits of the foregoing analysis. All experiments were performed with alumina fibers and aluminum metal. The experiments reported here were performed with the fibers initially at a temperature significantly below the metal melting point. This is the case of practical interest for the fabrication of many fiber-reinforced metal components, including, for example, diesel engine pistons. L.J. MASUR, formerly a Graduate Student with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, is Senior Scientist with the American Superconductor Corporation, Cambridge, MA 02139. A. MORTENSEN, Assistant Professor, J.A. CORNIE, Principal Research Associate, and M.C. FLEMINGS, Professor and Department Head, are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted June 7, 1988. METALLURGICAL TRANSACTIONS A
II. E X P E R I M E N T A L APPARATUS AND PROCEDURE
A. Fiber Preform Preparation SAFFIL* fibers were obtained from Imperial Chem*SAFFIL is a trademark of ICI Americas, Inc., Wilmington, DE.
ical Industries, London, England. SAFFIL is a nominally 3-/.Lm-diameter, delta-alumina fiber that is chopped and pressed into disk-shaped prcforms. The preform fabrication operation tends to align the fiber axes perpendicular to the pressing direction, resulting in a two-dimensional random arrangement of fibers. The preforms used in this study were 100 m m in diameter by 15-mm thick and featured a nominal fiber density of 24 vol pct. Cylindrical plugs were cut from the mother preform using a knife-edged cutter 17 m m in internal diameter. These plugs were then tightly fitted into quartz tubes 17 m m in internal diameter and 1 mm in wall thickness. Their orientation was such that metal infiltration was perpendicular to the fiber axes. In these experiments, either two or three plugs were placed atop one another within the quartz tube, resulting in fiber pre
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