On the Origin of Anomalous Eutectic Growth from Undercooled Melts: Why Re-melting is not a Plausible Explanation

Ag-Cu melt at the equilibrium eutectic composition has been undercooled using a melt fluxing technique. The resulting samples have been sectioned through the nucleation point and the spatial distribution of anomalous eutectic has been quantified. This is shown to be highly inhomogeneous, with the volume of anomalous material decreasing approximately linearly with distance from the nucleation site. In samples at low undercooling the volume fraction of anomalous eutectic near the nucleation site is around an order of magnitude greater than the calculated recalescence solid fraction. As such, any model for the origin of the anomalous eutectic invoking partial remelting of this initial solid is shown to be infeasible. An alternative model, based on a kinetic shift of the eutectic point during rapid solidification is proposed.