Fabrication and mechanical properties of Al/Al 2 O 3 composite bodies by reactive infiltration of molten Al into SiO 2 p
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Al/Al2O3 composites were fabricated by a displacement reaction between SiO2 and molten Al. In this study, fabrication of Al/Al2O3 composites was attempted by means of reactive infiltration to provide variation of their mechanical properties. SiO2 preforms having various porosities and pore size distributions were prepared by sintering the powder at different temperatures between 1273 and 1723 K. Molten Al was infiltrated at 1373 K without application of pressure. Infiltration kinetics were studied and the microstructures of the composite bodies were observed by means of scanning electron microscopy (with energy dispersive x-ray microanalysis), wave dispersive x-ray microanalysis, and x-ray diffractions. The infiltrated specimens were mainly composed of Al and ␣–Al2O3 phases, and the Si content was less than 5 at.%. Volume fraction of Al phase in the composite bodies was not altered very much with the porosities of the SiO2 preforms because of the difficulty in filling out the entire pore space. Properties and microstructures of Al/Al2O3 composites, however, were dependent on the sintering temperature of the SiO2 preforms. In the case of low sintering temperature, a thick Al channel existed, which deformed upon compression. In the case of high sintering temperature, the microstructure became homogeneous and had thinner Al channels. The composite bodies became brittle. The deformation behavior was shown to be changed from ductile to brittle as an increase of the sintering temperature of the preforms.
I. INTRODUCTION
In the 1990s, a method of fabricating Al/Al2O3 composite materials was proposed in Japan1 and the United States independently. This method takes advantage of a displacement reaction between molten Al and SiO2 as follows: 4Al(l) + 3SiO2(s) ⳱ 2Al2O3(s) + 3Si(in Al)
. (1)
This method is known as one example of the so-called “in situ composites”3 because the composite microstructures are formed spontaneously during processing of the materials. The obtained Al/Al2O3 composite microstructures resemble those obtained by direct oxidation of molten Al,4–6 where three-dimensional Al2O3 networks exist together with Al channels. In the case of the Al/Al2O3 composites by the above reaction [Eq. (1)], an interesting feature was reported2,3: the original SiO2 bodies can be transformed into the composites almost without changing their shape and size. This indicates potential capability for the near-net shape production of the composites.3 a)
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There have been other attempts of fabricating Al/Al2O3 composites, which are related to the above displacement reaction. Similar composites have been obtained by the reaction between mullite (Al6Si2O13) and molten Al7–10 (shown below), but the composites have larger volume fraction of Al2O3 than the case shown by Eq. (1).
J. Mater. Res., Vol. 15, No. 11, Nov 2000 Downloaded: 11 Mar 2015
(8 + x) Al + 3Al6Si2O13 ⳱ 13Al2O3 + 6Si + xAl
. (2)
Volume fraction of Al2O3 in the composites shown by Eq. (1
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