Fabrication and mechanical properties of Al/Al₂O₃ composite bodies by reactive infiltration of molten Al into SiO₂ preform

Abstract

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 α–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.