Anisotropic characteristic in HDDR Nd₁₃Fe₈₀B₇

The function of disproportionation and desorption stages of hydrogenation-disproportionation-desorption-recombination (HDDR) process in the formation of magnetic anisotropy was studied. The results showed that degree of anisotropy (DOA) of Nd₁₃Fe₈₀B₇ induced by appropriate HDDR process is comparable with that of Nd₁₃Fe_80-xB₇M_x (M=Co, Zr or Ga), however, the moder-ate coercive force of Nd₁₃Fe₈₀B₇ magnetic powder led to an undesirable (BH)_max of 104 kJ/m³ in bonded magnet. Experiments demonstrated that a relatively short disproportionation time, combined with a high desorption temperature and slow desorption rate, during HDDR process is beneficial to anisotropy attainment, but HDDR Nd₁₃Fe₈₀B₇ magnetic powder becomes isotropic if the dispropor-tionation time is longer than a certain period. This phenomenon strongly indicated that the origin of anisotropy in NdFeB-type HDDR material is contributed by disproportionation stage. XRD (X-ray Diffraction) analysis and TEM (Transmission Electron Mi-croscope) observation told that no other phase except NdH₂, α-Fe and Fe₂B has been found in the disproportionation step. The for-mation of HDDR Nd₁₃Fe₈₀B₇ anisotropy might be related to the early lamella disproportionation structure.