Fabrication and mechanical properties of α-Al2O3/β-Al2O3/Al/Si composites by liquid displacement reaction

Al2O3/metal composites were fabricated by heating three kinds of commercial mullite refractories in contact with Al, and their mechanical properties were investigated. Aluminum reacted with the mullite and SiO2-glass constituting the mullite refractories and changed them into α-Al2O3 and Si. Simultaneously, β-Al2O3 was formed by the reactions among α-Al2O3 and sodium and potassium oxides in the glassy phase. Also, Al penetrated into the α-Al2O3/β-Al2O3/Si composite by partly dissolving Si. Finally, the mullite refractories were changed into α-Al2O3/β-Al2O3/Al/Si composites. The phase contents, microstructures and mechanical properties of the resulting composites varied with the composition of the refractories. The content of β-Al2O3 in the composite was lowest at the lowest Na2O and K2O contents in the refractories. Silicon in the composite had its highest content at the highest SiO2 content. The composite fabricated from SiO2/Al2O3 (in mol) (SAR) = 1.85 consisted of 2–5 μm Al2O3 grains embedded in metal, but that from SAR = 1.05 showed a complicated microstructure with small and large grains. The bending strength of the composites fabricated from the refractories of SAR = 1.85, 1.24, and 1.05 were 327, 405 and 421 MPa, respectively. Also, the corresponding fracture toughness values were 5.2, 6.1, and 5.5 MPa m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} $$ \end{document}, respectively.