Eutectic microstructures in dilute Al-Ce and Al-Co alloys

Al-Ce and Al-Co binary alloys with compositions of 0.5, 1.0, and 3.0 at.% were arc-melted, allowed to solidify, and then characterized by a combination of X-ray diffraction and electron microscopy techniques. In case of the Al-Ce system, alpha-Al and Al11Ce3 phases were observed for all three compositions. The 0.5% and 1.0 at.% Al-Ce alloy microstructures contain pro-eutectic alpha-Al and a alpha-Al/Al11Ce3 eutectic, whereas the 3 at.% Al-Ce alloy is fully eutectic. These eutectics are lamellar in each case. The Al-Co system reveals pro-eutectic alpha-Al phase and an Al/Al9Co2 eutectic for the 0.5 at.% composition, a largely eutectic microstructure for the 1 at.% alloy, and dendrites of the Al9Co2 phase, surrounded by a sheath of alpha-Al, with pockets of eutectic between these features for the 3 at.% composition. For the 0.5 at.% and 1 at.% Al-Co alloys the eutectic is rod-like. The orientation relationships between the intermetallic and alpha-Al phase were determined for the eutectics using electron diffraction, and the morphology was related to the interfacial lattice matching between the phases.