As explained above, NdFeB powder is an intermediate material rather than a finished product. In industrial production, it can follow several different processing routes. Depending on the target magnet type, manufacturers use different Neodymium Iron Boron powder forms with specific particle characteristics and magnetic properties. The table below gives an overview of the typical Nd-Fe-B powder types used in the main Neodymium magnet manufacturing routes.
In practice, different NdFeB powders are supplied by a small number of specialized manufacturers. Rapidly quenched Nd-Fe-B powders for hot pressed magnets can be purchased from Magnequench and a few Chinese powder producers. Ultra-fine Neodymium Iron Boron powders for sintered Neodymium magnets have very small particle size and are classified as dangerous goods, so transport conditions are strict and, especially after the introduction of dual-use export control regulations, exporting them overseas has become extremely difficult.
Isotropic NdFeB powders for bonded magnets are produced by Magnequench and Chinese suppliers, and today almost all NdFeB powder exported from China belongs to this category. Anisotropic NdFeB powders for bonded magnets include crushed hot pressed material supplied by Magnequench and HDDR powders made by Japanese and Chinese manufacturers.
In our day-to-day business, most enquiries we receive about Nd-Fe-B powder fall into two categories: sintered-magnet powders, and isotropic NdFeB micro powder used in magnetic miniature robots research. Both types are classified as dangerous goods, and strict shipping rules make them very difficult to supply to overseas customers. As sintered-magnet powders are so hard to export and the export volume of other special powders is very limited, when we talk about Nd-Fe-B powder in our product range, we mainly mean the isotropic and anisotropic NdFeB powders used for bonded Neodymium magnets.
In our product range, “NdFeB powder” mainly refers to the isotropic and anisotropic NdFeB powders used for bonded Neodymium magnets. Some customers believe that, if the particle size is made fine enough, these bonded NdFeB powders could also be used to produce sintered Neodymium magnets. In reality, this is not feasible.
Sintered Neodymium magnets rely on magnetic field alignment and liquid-phase sintering of fine Nd2Fe14B grains. The powder is typically 3–5 μm particles with carefully controlled composition, grain-boundary phases, oxygen content and surface state to ensure good densification and high coercivity after sintering.
Isotropic NdFeB powders for bonded magnets are characterised by randomly oriented easy magnetisation axes. This random orientation is “built in” during their production. Even if such powders are compacted in a magnetic field and then sintered, the microstructure will not reorganise into a well-aligned, high-performance anisotropic sintered magnet. At best, they could form a low-performance, nearly isotropic sintered block, with much lower remanence and energy product than a normal anisotropic sintered Neodymium magnet. From an industrial point of view, this is not meaningful, because the sintering cost is high while the performance is poor.
Anisotropic NdFeB powders used for bonded magnets are usually produced by HDDR or by crushing hot pressed material. In these powders, the anisotropy is inside each particle, as an internal crystallographic texture. The composition and microstructure are optimised for bonded magnets, not for conventional liquid-phase sintering. If one tries to mill these powders down to the 3–5 μm range required for sintered magnets, the internal texture that gives the powder its anisotropy is largely destroyed, so the powder behaves more like an isotropic powder.
