Orientation growth of peritectic phase in directionally solidified NdFeB permanent magnet alloys

Directional solidification experiments were performed on the NdFeB rare earth permanent magnets. The solidification behaviors of the intermetallic compound Nd₂Fe₁₄B (T₁) phase were analyzed by X-ray diffraction (XRD) analysis method and Bitter magnetic domain observation. The results showed that the morphology and the preferred orientation of Nd₂Fe₁₄B were related to the composition and solidification rate. At lower solidification rates (less than 10 μm·s^-1), T₁ phase grew with a faceted interface and exhibited a high tendency of the anisotropic growth. With the increase of the growth rate, the Ti grain became refined, and the growth interface of T₁ phase tended to be roughened. The axial preferred orientation of T₁ phase was close to the direction of the easy magnetization axis, i.e. c-axis [001] during directional solidification Nd_11.76Fe_82.36B_5.88 alloy. In addition, the preferred orientation of T₁ phase gradually deviated from the c-axis [001] to a-axis [100] with increased solidification rate in Nd_13.5Fe_79.75B_6.75 alloy. The reason might be that the solidification rate changed the driving forces, i.e. the growth rates in the [100] and [001] directions of the T₁ phase.