On the existence of metastable microheterogeneities in metallic melts

Whether a molten alloy after melting is homogeneous or not on the atomic scale has been an issue for many experimental investigations, which have used a manifold of techniques. In most of these investigations, the anomalies in measured property/temperature curves, which were found at temperatures well above the liquidus temperature, have been interpreted as the indications for the existence of a dissolution process of alloy microheterogeneities which were inherited from the precursor solid alloy. In this report new results on the structural and transport properties of Al-Si and Al-Cu alloys are presented. In particular, new accurate measurements of the viscosity and the density of Al-Cu liquid alloys are reported. A large difference between the quantities measured during heating and the quantities obtained after the subsequent cooling was observed in narrow composition ranges corresponding to the stoichiometric compositions AlCu and Al₂Cu. Furthermore, the ultrasound velocity and viscosity measurements on alloys, which are suggested to be used as heat carriers in nuclear power plants (Pb-Bi, Pb-Sn and Ga-In alloys of near-eutectic concentrations), are presented. The results show that microheterogeneities exist in the melts at their planned temperatures of use.