The Microstructures of Rapidly Solidified Hyper-eutectic AlBe Alloys

Several alloys of hyper-eutectic composition (in the range 4.4-20.0 at% Be) have been rapidly solidified by melt-spinning in an He environment. For low solute compositions, the microstructure consists of cells elongated in the transverse direction of the ribbons. The intercellular regions consist of a refined dispersion of Be particles whereas the cells themselves (the intracellular regions) contain a small supersaturation of Be. As the solute concentration is increased the microstructure at first becomes more refined, consisting of a dispersion of Be particles (≈ 50 Å in diameter with an interparticle spacing of ≈ 200 å) in an Al matrix. At higher concentrations, a bimodal distribution of Be particles is present in the Al matrix, the finer precipitates being similar in appearance to those described above, and the coarser particles being ∼0.1-0.15 μm in diameter. These various microstructures may be most satisfactorily described on the basis of a set of metastable phase transformations involving a monotectic reaction. In this way, the refined distribution of Be particles is a product of this reaction, whereas the larger particles are thought to form during a pro-monotectic transition. © 1985