Solidification from Undercooled Melts: Nucleation and Crystal Growth

Kurzfassung

Electromagnetic levitation technique is applied to containerlessly undercool bulk samples in diameter of 6-8 mm. The technique is combined with the diagnostic means at the Institut Laue Langevin and the European Synchrotron Radiation Facility for elastic neutron and high intensity X-ray diffraction on undercooled metallic melts Nucleation and dendrite growth behavior in undercooled melts of metals and alloys are studied by measurements of undercooling and the dendrite growth velocity as a function of undercooling using a high speed camera. The effect of solute trapping is discussed in the regime of large undercoolings and rapid crystal growth in dilute Ni-Zr alloys. Also, the fragmentation of dendrites is studied. Special emphasis is placed on the influence of convection on the critical undercoolings for microstructural transitions. In addition, we present measurements of dendrite growth in Ni-Al alloys of hypo- and hyper-stoichiometric composition. The experimental results are analyzed within models of solute and disorder trapping of rapid solidification. Finally, results of measurements of dendrite growth in undercooled Si-Co alloys are presented, which show an anomalous behavior in their velocity-undercooling relationship. The presentation will close with the discussion of the perspectives to use colloidal systems as model systems to study and to describe solidification of metallic melts.