Study on the Influence of Annealing and Ball Milling on the Magnetic Properties of HDDR Nd-Fe-B Magnetic Powder.

The Nd-Fe-B anisotropic magnetic powders were subjected to tempering and ball milling processes. Analysis of the magnetic properties, structure, and physical phase revealed that the following: the integrated magnetic properties of the magnetic powder were the best when the tempering temperature and time were separately 650 °C and 20 min, for DOA = 0.73, B_r = 6.547 kGs, H_cj = 12.255 kOe, and (BH)_max = 7.117 MGOe. When the DR temperature is 860 °C, the tempering temperature is 650 °C, and the tempering time is 20 min, the ideal magnetic properties of the magnetic powder are DOA = 0.69, B_r = 6.238 kGs, H_cj = 14.67 kOe, and (BH)_max = 7.060 MGOe. The integrated magnetic properties of the magnetic powders were optimal when the ball milling speed, time, and doped Cu content were 350 rpm, 2 h, and 10 wt%, for DOA = 0.62, B_r = 4.96 kGs, H_cj = 9.86 kOe, and (BH)_max = 4.39 MGOe. The ideal tempering temperature and time can promote the diffusion of Nd-rich phase to the grain boundaries, strengthen the pinning effect on the magnetic domains, and improve the coercivity of the magnetic powder. The ideal ball milling speed and time can effectively reduce the particle size of the main phase particles of the magnetic powder and the large particles of the Nd-rich phase, so that the Nd-rich phase is uniformly distributed at the grain boundaries, to achieve the effect of de-magnetization coupling and improve the coercivity of the magnetic powder. After ball milling the magnetic powder doped with an appropriate amount of Cu powder, Cu induces the precipitation of a certain amount of Nd in the main phase of Nd₂Fe₁₄B. This Nd is uniformly distributed at the grain boundaries, achieving the effect of repairing the grain boundaries, thereby improving the coercivity of the magnetic powder. [ABSTRACT FROM AUTHOR]