Columnar dendritic solidification in a metal- matrix composite
- PDF / 4,423,601 Bytes
- 13 Pages / 613 x 788.28 pts Page_size
- 12 Downloads / 253 Views
I.
INTRODUCTION
A s technological and commercial interest in metal matrix composites increases, much attention is being paid to casting as a composite fabrication technique. Casting processes have the advantages of relative simplicity and potential for low-cost production of near-net shape composite components. A number of researchers have recently reported studies on infiltration of fiber bundles by molten metal, interracial reactions during the casting process, and the properties of cast metal-matrix composites. A review has been given of articles on these aspects of solidification processing, with special attention to composites of carbon and silicon carbide fibers infiltrated with aluminum alloys. 1,2 To date, the solidification behavior of alloys in the presence of fibers has received only scant attention. In this work we pressure infiltrate a fibrous preform and allow it to solidify. We then remelt the matrix and allow it to resolidify. The technique allows independent control of the temperature gradient, G, and the growth rate, V. The matrix alloy, A1-4.5 wt pct Cu, was chosen primarily because of the existence of a large bank of data concerning solidification (and in particular steady state solidification) in the A1-Cu systemfl-l~ This choice was further justified by the fact that copper as an alloying additive in aluminum is inert with respect to the fibers as will be shown in what follows.
AVCO Specialty Materials Division, Lowell, MA. The microstructure of these fibers is complex, and they present at their surface a carbon-rich layer, tl Cylindrical composite samples 5 mm in diameter by about 70 mm long were cast using the experimental pressure casting procedure outlined in Figure 1. The fibers were packed tightly into small bundles about 80 mm in length and 3 mm in diameter and held together at their ends with a few narrow windings of fiber+--gate
(a)
l(b)
l graphite mold
Electrical heater
Insulation material .Graphite mold ~Fibers Steel pressure chamber
(c) II.
SAMPLE PREPARATION A N D EXAMINATION
Piston
The metal-matrix alloy, A1-4.5 wt pct Cu, contained less than 0.05 wt pct impurities. The fibers were large silicon carbide fibers, 140/xm in diameter, manufactured by ANDREAS 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, 77 Massachusetts Avenue, Cambridge, MA 02139. Manuscript submitted March 12, 1987. METALLURGICALTRANSACTIONS A
Molten Alloy Composite
(d) Fig. 1--The procedure followed to produce samples. Fibers are packed into a bundle (a), inserted into a graphite mold (b), and preheated in the squeeze casing apparatus (c) before pouring the metal and pressurization (d). VOLUME 19A, MARCH 1988--709
glass tape of total thickness 1 mm. These bundles were then inserted with the fiberglass tape winding at their ends into a flat graphite mold with several cylindrical cavities 80 mm in length and 5 mm in diamet
Data Loading...
