Reactions during infiltration of

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I.

INTRODUCTION

I N F I L T R A T I O N of molten metal into a fiber preform is a convenient method to manufacture metal-matrix composites. During the last 2 decades, a large number of experiments have been made on aluminum-base alloys combined with alumina preforms and other types of reinforcements. The most comprehensive work in this area was recently published by Oh and Mortensen and their co-workers, i~-61 Besides alumina preforms, silicon carbide preforms and graphite preforms have been used to produce aluminum-matrix composites. However, in the latter case, a reaction occurs between the graphite or the carbides on one hand and liquid aluminum on the other, leading to the formation of aluminum carbide. It is by now a well-known fact that even a limited amount of aluminum carbide has a negative effect on the mechanical properties of the composite material. Recently, a series of experiments were made in the system A1-Ti-C, where the reaction between graphite and liquid aluminum alloyed with titanium was studied. 17] Equilibrium experiments have also been made, i81 yielding the phase diagram A1-Ti-C. The experimental and theoretical results showed that TiC was more stable than aluminum carbide at high temperatures. In order to analyze if it would be possible to produce a composite consisting of graphite fibers, securely bonded to the matrix, and separated from each other by freely formed titanium carbides, a series of infiltration experiments were made.

Figure 1. A SAFFIL* paper was used to fix the fiber *SAFFIL is a trademark of ICI Americas, Inc., Wilmington, DE.

preform. This paper was also used as a filter to break the alumina skin on the melt surface. A schematic drawing of the infiltration experimental setup used is shown in Figure 2. It can be seen from the figure that it is a low-pressure infiltration and casting system, where the applied gas pressure forces the melt up into the preform. The melt temperature was measured in the bottom of the alumina crucible. A high-frequency induction-heated radiative body, made of graphite, was used as a source of heat. The pressure vessel used was a PYREX* tube with *PYREX is a trademark of Coming Glass Works, Corning, NY.

an internal diameter of 55 m m and wall thickness of 5 mm. Before heating and pressurization, the vessel was evacuated and subsequently filled with argon; argon was then flushed through the vessel for 5 minutes. The heating and infiltration sequence were as follows: the sample was melted and heated to the infiltration temperature; the melt was held at this temperature for 2 minutes to allow dissolution of the titanium aluminide phase; the vessel was then pressurized, for 1 or 5 minutes; and the vessel was then depressurized, and the samples were subsequently solidified. The experimental conditions are shown in Table I.

II.

EXPERIMENTAL

The experimental equipment is similar in design to that of Oh et al. ij'21 The experiment consists of two steps: first, the fabrication of the graphite fiber preform; and second, the actual infiltration. As in