Al 2 O 3 /Al particle-reinforced aluminum matrix composite by displacement reaction
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Al2 O3yAl particle-reinforced aluminum matrix composite by displacement reaction M. R. Hanabe and P. B. Aswath Materials Science and Engineering Program, University of Texas at Arlington, P.O. Box 19031, Arlington, Texas 76019 (Received 12 February 1995; accepted 25 January 1996)
The development of a novel Al matrix composite is described based on a simple displacement reaction when an SiO2 particulate preform is brought into contact with liquid Al at temperatures between 1273 and 1373 K. This interaction leads to the wetting of the SiO2 particles by Al and its eventual transformation to a composite with Al2 O3yAl particles in an Al matrix. Infiltration of the preform as induced by this reaction takes place with the simultaneous formation of the Al2 O3yAl particles in situ. Synthesis of engineered multiphase composites, wherein reinforcements of other materials incorporated into the preform and reacted with liquid Al, is also presented.
I. INTRODUCTION
A significant development in the processing of Al matrix composites in recent years has been the concept of pressureless infiltration of a melt into porous preforms.1,2 The major attraction of melt infiltration methods comes from the low processing temperature, the absence of external pressures to aid infiltration, and the ability to form complex shapes. In addition to this, melt infiltration results in near net-shape fabrication. In one of the pressureless melt infiltration techniques, an Al alloy billet is kept in contact with a particulate or a fiber preform and heated to temperatures between 973 and 1273 K in a N2 or a N2 -rich Ar atmosphere.1,2 Wetting of the preform material takes place, and the melt spontaneously infiltrates and fills up the pores of the preform. High reinforcement loadings are possible (up to 70% by volume). Mandatory to this effect is the presence of about 5% by weight each of Si and Mg and a nitrogen atmosphere. Although the exact mechanism of infiltration is not yet clear, it was observed that the melt fills up the pores by a process of reaction-induced wetting. In the case of Al2 O3 particulate reinforcements, vaporization of Mg from the melt and its subsequent reaction with trace amounts of oxygen in the nitrogen gas leads to the formation of a MgO coating on each of the Al2 O3 particles ahead of the infiltration front.3 Reaction of Al with this MgO layer leads to the formation of MgAl2 O4 at the Al2 O3yAl interface. This reaction could be acting as the driving force for infiltration. A similar interaction between Al and MgO leading to spinel formation and its continuous presence as a surface oxide layer governs the generation of an Al2 O3 -matrix composite in the DIMOX process.4,6 Wetting of a ceramic oxide as induced by a reaction with a liquid metal is an important factor for the pres1562
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 6, Jun 1996
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sureless infiltration technique. This factor is governed by the decrease in the interfacial tension gsl
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