Investigation of nucleation in undercooled metal melts

Abstract

Containerless processing is an effective tool for undercooling metallic melts far below their equilibrium melting temperatures. By using such levitation techniques the dominating heterogeneous nucleation on container-walls is completely eliminated. Furthermore, if the experiments are performed under clean environmental conditions, heterogeneous nucleation on free surfaces is also greatly reduced. In this work both electromagnetic and electrostatic levitation techniques are used for a comparative investigation of nucleation in undercooled metallic metals. In case of electromagnetic levitation samples in a diameter of 7 mm are processed within high purity inert gas atmosphere while in case of electrostatic levitation samples in a diameter of 2 mm are processed in ultra high vacuum. With a modified model by Skripov a statistical analysis of the distribution function of the undercoolings measured in one experiment run consisting of at least 100 undercooling cycles is conducted which provides information about the physical nature of different nucleation mechanism depending on experiment conditions. The project was funded by Deutsche Forschungsgemeinschaft, under contract No. HE 1601/21.