Metallography of a melt-quenched aluminum-cobalt alloy

Rapid quenching from the melt of an Al-5 wt.% Co alloy has resulted in the formation of a supersaturated solid solution at very high cooling rates as obtained in the gun technique. With decreasing cooling rate (and increasing thickness of the specimen), e.g., in melt-spun condition, a variety of microstructures has been produced consisting of fine dendritic patterns, cellular-dendritic structures, and precipitation of coarse intermetallic particles. Two metastable phases have also been detected—one with a bcc structure and a = 0.286 nm corresponding to β-AlCo, and the other having an fcc structure with a lattice parameter a = 0.52 nm. Electron microscopy, electron diffraction, and x-ray microanalysis have been extensively employed to fully characterize the phases present in the melt-quenched alloy.