Anisotropic NdFeB Powder

Anisotropic NdFeB powder is mainly used to produce anisotropic bonded Neodymium magnets by mixing it with selected polymer binders. These magnets are formed by injection or compression molding, similar to bonded magnets made from isotropic NdFeB powder. However, during molding they must be exposed to an external alignment field, which orients the individual powder particles and significantly boosts the magnet’s performance.

Anisotropic NdFeB powder is typically produced by two main methods: the hydrogenation-disproportionation-desorption-recombination (HDDR) process or by crushing hot-deformed Neodymium magnets.

In the HDDR process, first reported by Takuo Takeshita and Ryoji Nakayama at Mitsubishi Materials (Japan) in 1989, a homogenized NdFeB alloy is heated in a hydrogen atmosphere and then dehydrogenated. This treatment refines the original 100–500 μm grains into a microstructure of anisotropically aligned grains with an average size of about 0.35 μm.

Alternatively, anisotropic hot-deformed magnets are produced by hot pressing isotropic, rapidly solidified NdFeB powder into dense magnets and then die upsetting them to introduce anisotropy. These hot-deformed magnets are subsequently crushed to the desired particle size to obtain anisotropic NdFeB powder.