Microstructure of an Al2O3/Metal Composite Containing an Al2O3 Filler Material

A ceramic matrix composite consisting of 100–200 μm Al2O3 grains (90 grit) embedded an Al2O3/metal matrix was examine. The matrix was produced by the directed oxidation of a molten Al alloy. The microstructure was studied by optical methods, x-ray diffraction and transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS). The matrix A12O3 was interconnected and present as ∼50–500 nm grains in ∼ 10–50 μm regions. Within these regions, the Al2O3 was separated by low angle. Al2O3/Al2O3 grain boundaries. The boundaries between regions consisted either of high angle Al2O3/Al2O3 boundaries with no grain boundary phase or of tortuous metal channels from 50 nm up to 1 μm in width. The metallic constituent within the regions was only partly interconnected, consisting of similar channels or isolated spheres of 1–500 nm. The metal consisted of Al and Si. Large fractions of the filler Al2O3 surface (∼50%) were directly bonded to the matrix Al2O3.