Electromagnetic levitation apparatus for investigations of the phase selection in undercooled melts by energy-dispersive x-ray diffraction

The metastable state of an undercooled melt can provide access to the formation of metastable phases whose crystallographic structures differ from their stable counterparts. The electromagnetic levitation technique is used here to undercool bulk melts without containers. This technique, combined with energy dispersive x-ray diffraction of synchrotron radiation, allows in situ study of the rapid crystallization of undercooled Ni-V alloys. The binary Ni-V alloy was chosen as a model system, because it shows phase competition of three different crystallographic phases, bcc, fcc, and an intermetallic phase of tetragonal structure at intermediate concentrations. The diffraction experiments provide for direct identification of the various crystalline phases formed from the nonequilibrium state of the undercooled melt. The phase selection is investigated as a function of undercooling temperature for Ni-V alloys of different concentrations. (C) 2000 American Institute of Physics. [S0034-6748(00)00910-2].