Grain Boundary Diffusion Technology

The traditional method of adding elements is to add them in the smelting process, that is, smelting Dy, Tb, Nd, Fe, B and other elements together, and Dy is distributed in the grain boundary and the main phase of the grain in the produced magnet. However, studies have shown that Dy at the grain boundary has the most significant effect on improving the coercivity, and the traditional method of adding elements is a bit “wasting resources”.

Japanese researchers first proposed the concept of “grain boundary diffusion”. They used a special process to make Dy only exist in the grain boundary without entering the grain through diffusion, which not only improved the performance of NdFeB materials, but also greatly reduced Dy The total amount of elements reduces the cost of materials. They deposited Dy vapor on the particle surface during the milling process, and the diffusion of Dy atoms along the grain boundaries occurred during the subsequent sintering process. Dy and Fe at the grain boundaries are antiferromagnetically coupled, and the material coercivity increases from 800kA/m to 1800kA/m with almost no reduction in remanence.

The damage of the magnet surface after machining can lead to the weakening of the magnetic properties, especially for small-sized samples, the coercive force decreases significantly, and the grain boundary diffusion technique can be used to repair and increase the magnetic properties of the magnet surface. At present, grain boundary diffusion technology has received extensive attention, and its preparation processes mainly include evaporation diffusion, magnetron sputtering, and surface coating.