Containerless Undercooled Melts: Ordering, Nucleation, and Dendrite Growth

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2015-11, Vol.46 (11), p.4921-4936
• Main Authors: Herlach, Dieter M., Binder, Sven, Galenko, Peter, Gegner, Jan, Holland-Moritz, Dirk, Klein, Stefan, Kolbe, Matthias, Volkmann, Thomas
• Format: Article
• Language: English
• Subjects: Alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Convection; Cooling; Dendritic structure; Electromagnetics; Materials Science; Metallic Materials; Metals; Nanotechnology; Neutrons; Nucleation; Order disorder; Structural Materials; Supercooling; Surfaces and Interfaces; Symposium: ICASP-4 (International Conference on Advanced Solidification Processing); Thin Films; Trapping; Undercooling
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-015-3052-8

Electromagnetic and electrostatic levitation are applied to containerless undercool and solidify metallic melts. A large undercooling range becomes accessible with the extra benefit that the freely suspended drop is accessible directly for in situ observation. The short-range order in undercooled melts is investigated by combining levitation with elastic neutron scattering and X-ray scattering using synchrotron radiation. Muon Spin Rotation ( µ SR) experiments show magnetic ordering in deeply undercooled Co 80 Pd 20 alloys. The onset of magnetic ordering stimulates nucleation. Results on nucleation undercooling of zirconium are presented showing the limit of maximum undercoolability set by the onset of homogeneous nucleation. Metastable phase diagrams are determined by applying energy-dispersive X-ray diffraction of Ni-V alloys with varying concentration. Nucleation is followed by crystal growth. Rapid dendrite growth velocity is measured on levitation-processed samples as a function of undercooling ∆ T by using high-speed video camera technique. Solute trapping in dilute solid solutions and disorder trapping in intermetallic compounds are experimentally verified. Measurements of glass-forming Cu-Zr alloy show a maximum in the V (∆ T ) relation that is indicative for diffusion-controlled growth. The influence of convection on dendrite growth of Al 50 Ni 50 is shown by comparative measurements of dendrite growth velocity on Earth and in reduced gravity. Eventually, faceting of a rough interface by convection is presented as observed on Ni 2 B alloys.