Effects of Tb Diffusion on Microstructure and Properties of Nd Fe B Magnets

DC magnetron sputtering technology were used to coat Tb films of different thicknesses on the unipolar surface of sintered NdFeB magnets, and the thermal diffusion and annealing treatment were carried out. The results show that,3.137 μm film thickness is the most coercivity of magnet most obviously, and under the heat treatment conditions of 850 ℃×7h+500 ℃×2 h, the best magnetic properties are obtained, and its coercivity increases from 872.36 kA/m to 1305.67 kA/m, the temperature coefficient of remanence α at 20-160 ℃ decreases from-0.1226%/℃ to-0.1230%/℃, which are slightly lower,but the temperature coefficient of coercivity β increases from-0.5534%/℃ to-0.5297%/℃. The microstructure of the near surface and deep part of the Tb diffusion magnet is observed by SEM, it can be found that the obvious(Nd,Tb)₂Fe₁₄B core-shell structure and the more uniform distribution of rich Nd phase are the main reasons for the improvement of the magnetic properties of the magnet.