Quantitative Analysis of Breakdown Criteria of Nd2Fe14B Compounds During Electromagnetic Vibration and Their Frequency-Dependent Solidification Structures/Magnetic Properties

In our previous work, we reported on the segmentation and alignment of Nd 2 Fe 14 B platelets in a semisolid slurry when two-step electromagnetic vibration (EMV) was imposed (Li and Tamura in Metall Mater Trans A 51A:2939−2956, 2020), in which the breakdown of developed Nd 2 Fe 14 B phases was presented qualitatively. In the present study, we quantitatively analyzed the breakdown criteria of the compound in Nd 70 Cu 30 –50 wt pct Nd 2 Fe 14 B alloys when considering the specimen setting condition and vibration frequencies after realizing the importance of a gap between the specimen and the container. Upon the imposition of EMV, there are two different vibration modes, i.e., the breakdown mode (BDM) and the simple harmonic vibration mode (SHVM) at a characteristic frequency, which depend on the initial phase angle. We analyzed critical vibration frequencies in terms of BDM or SHVM when considering the initial phase angle and the specimen location. More general vibration patterns were presented, and the breakdown energy was given in a wide vibration frequency range. The structures of alloys solidified at diffident vibration frequencies were observed, which could be well elucidated when considering the breakdown energy and movement behavior at the individual frequency. The magnetic properties were measured using a vibrating sample magnetometer (VSM), which showed good agreement with solidification structures. The present analysis can be applicable to mechanical vibrations as well, by which some Nd 2 Fe 14 B fine platelets have been observed. Hence, the results may provide a guideline for scaling up in EMV processing and optimizing processing parameters and moreover, determining specifications of a mechanical vibrator to refine the Nd 2 Fe 14 B phase.