Direct determination of metastable phase diagram by synchrotron radiation experiments on undercooled metallic melts

The phase selection process during the crystallization of undercooled metal lic melts is studied in situ by combining the electromagnetic levitation te chnique with energy dispersive x-ray diffraction of synchrotron radiation. The crystallization of metastable bcc phase in binary Ni-V alloys was ident ified. A metastable phase diagram of NI-V alloy is constructed, which shows the primarily solidifying phase as a function of composition and undercool ing. The analysis within nucleation theory emphasizes the important role of metal oxide as a heterogeneous nucleation site controlling the phase selec tion.