Non-Equilibrium Solidification of Undercooled Metallic Melts

被引:69
作者
Herlach, Dieter M. [1 ]
机构
[1] DLR, Deutsch Zentrum Luft & Raumfahrt, Inst Mat Phys Weltraum, D-51147 Cologne, Germany
关键词
undercooling; containerless solidification; metastable solids; dendrite growth; supersaturated alloys; disordered superlattices; grain refinement; forced convection; microgravity; CRYSTAL-GROWTH; RAPID SOLIDIFICATION; METASTABLE PHASE; ELECTROMAGNETIC-LEVITATION; DENDRITIC SOLIDIFICATION; INTERFACE; GLASS; TEMPERATURE; TRANSITION; DIFFUSION;
D O I
10.3390/met4020196
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
If a liquid is undercooled below its equilibrium melting temperature an excess Gibbs free energy is created. This gives access to solidification of metastable solids under non-equilibrium conditions. In the present work, techniques of containerless processing are applied. Electromagnetic and electrostatic levitation enable to freely suspend a liquid drop of a few millimeters in diameter. Heterogeneous nucleation on container walls is completely avoided leading to large undercoolings. The freely suspended drop is accessible for direct observation of rapid solidification under conditions far away from equilibrium by applying proper diagnostic means. Nucleation of metastable crystalline phases is monitored by X-ray diffraction using synchrotron radiation during non-equilibrium solidification. While nucleation preselects the crystallographic phase, subsequent crystal growth controls the microstructure evolution. Metastable microstructures are obtained from deeply undercooled melts as supersaturated solid solutions, disordered superlattice structures of intermetallics. Nucleation and crystal growth take place by heat and mass transport. Comparative experiments in reduced gravity allow for investigations on how forced convection can be used to alter the transport processes and design materials by using undercooling and convection as process parameters.
引用
收藏
页码:196 / 234
页数:39
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