Directional Solidification of Near-azeotropic CuMn-alloys: A Model System for the Investigation of Morphology and Segregation Phenomena

Copper-manganese alloys of a near-azeotropic composition show a rather different solidification behaviour at only slight variations of the concentration. The reason for this is the fact that during the directional solidification vertically upwards the less dense manganese or the more dense copper is enriched in front of the moving solid-liquid interface depending on a hypo- or hyperazeotropic alloy concentration, respectively. Therefore, in the samples solidifying at low solidification velocities with a planar interface a convective unstable or stable behaviour is found, which leads to different concentration profiles in the solidified alloy. At higher solidification rates cellular and dendritic morphologies are produced in a reproducible way and can be excellently metallographically preparated and visualized. In this paper a survey of typical hyper- and hypoazeotropic non-planar morphologies in radial cross-sections is presented. This morphological structures are the basis for statistical evaluations of he patterns describing the interaction between the interface and the heat and mass transfer in the melt.