Observation of a metastable phase during solidification of undercooled Nd - Fe - B alloy melts by in situ diffraction experiments using synchrotron radiation

The electromagnetic levitation technique was combined with the diagnostic means at the European Synchrotron Radiation Facility in Grenoble to study in situ the phase selection during solidification of undercooled Nd - Fe - B melts. By energy dispersive diffraction experiments with synchrotron radiation on levitated Nd - Fe - B alloys complete diffraction spectra were recorded within a time interval of a few seconds. Owing to the short measuring time the primary crystallization of a metastable phase was observed that initiates the solidification of hard magnetic Nd 2 Fe 14 B 1 phase. The metastable phase dissolves subsequently and cannot be detected in the as-solidified sample at the ambient temperature. By analyzing the diffraction spectra the metastable phase is identified as a ternary extension of the rhombohedral Nd 2 Fe 17 phase being stable in binary Nd - Fe alloys.