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 forma tion of metastable phases whose crystallographic structures differ from the ir stable counterparts. The electromagnetic levitation technique is used he re to undercool bulk melts without containers. This technique, combined wit h energy dispersive x-ray diffraction of synchrotron radiation, allows in s itu study of the rapid crystallization of undercooled Ni-V alloys. The bina ry Ni-V alloy was chosen as a model system, because it shows phase competit ion of three different crystallographic phases, bcc, fcc, and an intermetal lic phase of tetragonal structure at intermediate concentrations. The diffr action experiments provide for direct identification of the various crystal line phases formed from the nonequilibrium state of the undercooled melt. T he phase selection is investigated as a function of undercooling temperatur e for Ni-V alloys of different concentrations. (C) 2000 American Institute of Physics. [S0034-6748(00)00910-2].