What is NdFeB dysprosium and terbium technology

Since the advent of NdFeB permanent magnet materials in the 1980s, they have been widely used in various fields such as automobiles, wind power, aerospace, and military industries with excellent magnetic properties. In recent years, the demand for wind power generation and new energy vehicles has continued to increase.  This puts forward higher requirements on the coercivity and temperature stability of NdFeB permanent magnet materials.
 Since the magnetocrystalline anisotropy field of the Dy2Fe14B phase is much stronger than that of the Nd2Fe14B phase, and the Curie temperature is relatively high, the coercive force and temperature stability of the material can be greatly improved, and the coercive force and use temperature requirements are higher.  In sintered NdFeB materials, the content of dysprosium is very high, and some can reach more than 10%.  Everyone knows that the price of heavy rare earth element dysprosium and terbium is relatively high, and a large amount of addition will increase the production cost of NdFeB. Therefore, how to reduce the amount of dysprosium and terbium under the premise of ensuring high coercivity and temperature stability has become an important issue.

The traditional element addition method is to add in the smelting process, that is, to smelt Dy, Tb and Nd, Fe, B and other elements together, and Dy is distributed in the grain boundary and the main phase of the grain in the finished 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 "a waste of 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 crystal through diffusion. This not only improved the performance of the neodymium iron boron material, but also greatly reduced the Dy  The total amount of elements reduces the cost of materials.  They deposited Dy vapor on the surface of the particles during the powdering process, and Dy atoms diffused along the grain boundaries during the subsequent sintering process.  Dy and Fe located at the grain boundary are antiferromagnetically coupled, and the coercivity of the material increases from 800kA/m to 1800kA/m with almost no reduction in remanence.
 The damage of the magnet surface after machining will lead to the weakening of the magnetic properties. Especially for small-sized samples, the coercive force decreases significantly. The grain boundary diffusion technology can be used to repair and increase the magnetic properties of the magnet surface.  At present, the grain boundary diffusion technology has received widespread attention, and its preparation processes mainly include evaporation diffusion, magnetron sputtering, surface coating and so on.