Crystal nucleation and dendrite growth of metastable phases in undercooled melts
Herlach, D. (2011) Crystal nucleation and dendrite growth of metastable phases in undercooled melts. Journal of Alloys and Compounds, 509S, pp. 513-517. Elsevier. DOI: 10.1016/j.jallcom.2010.11.186.
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An undercooled melt possesses an enhanced free enthalpy that opens up the possibility to crystallize metastable crystalline solids in competition with their stable counterparts. Crystal nucleation selects the crystallographic phase whereas the growth dynamics controls microstructure evolution. We apply containerless processing techniques such as electromagnetic and electrostatic levitation to containerlesss undercool and solidify metallic melts. Owing to the complete avoidance of heterogeneous nucleation on container-walls a large undercooling range becomes accessible with the extra benefit that the freely suspended drop is direct accessible for in situ observation of crystallization far away from equilibrium. Results of investigations of maximum undercoolability on pure zirconium are presented showing the limit of maximum undercoolability set by the onset of homogeneous nucleation. Rapid dendrite growth is measured as a function of undercooling by a high-speed camera and analysed within extended theories of non-equilibrium solidification. In such both supersaturated solid solutions and disordered superlattice structure of intermetallics are formed at high growth velocities. A sharp interface theory of dendrite growth is capable to describe the non-equilibrium solidification phenomena during rapid crystallization of deeply undercooled melts. Eventually, anomalous growth behaviour of Al-rich Al–Ni alloys is presented, which may be caused by forced convection.
|Title:||Crystal nucleation and dendrite growth of metastable phases in undercooled melts|
|Journal or Publication Title:||Journal of Alloys and Compounds|
|In ISI Web of Science:||Yes|
|Page Range:||pp. 513-517|
|Keywords:||Crystal nucleation, dendrite growth, metastable solids, containerless processing|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Space|
|HGF - Program Themes:||W FR - Forschung unter Weltraumbedingungen|
|DLR - Research area:||Space|
|DLR - Program:||W FR - Forschung unter Weltraumbedingungen|
|DLR - Research theme (Project):||W - Vorhaben Materialwissenschaftliche Forschung|
|Institutes and Institutions:||Institute of Materials Physics in Space|
|Deposited By:||Dieter Herlach|
|Deposited On:||08 Jun 2011 08:08|
|Last Modified:||04 Apr 2013 16:29|
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