Various binary Al-Co alloys were investigated by using scanning electron microscopy, polarized light metallography, X-ray powder and single crystal diffraction methods. Needle-like decagonal prisms were observed, in the surface habits of the as-cast alloys, by means of scanning electron microscopy. Metallographic investigations in polarized light showed that the decagonal prisms were not truly monocrystalline. They also exhibited a complex microstructure that comprised 2 different types of grain (twinned and untwinned); indicating 2 different phases. Weissenberg photographs of decagonal prisms revealed a splitting of the diffraction reflections into 5 partial spots, due to polysynthetic twinning. The diffraction motif of Weissenberg photographs, with the rotation axis perpendicular to the basal plane of a decagonal prism, revealed decagonal pseudo-symmetry.

U.Burkhardt, M.Ellner, Y.Grin: Zeitschrift für Metallkunde, 1995, 86[4], 281-8