A subsequent crystallization heat treatment promotes grain growth to roughly 50–200 nm, achieving high intrinsic coercivity in submicron grains smaller than the single-domain critical size of Nd2Fe14B. It is important to note that isotropic NdFeB powder is not suitable for producing sintered Neodymium magnets
Isotropic NdFeB powder is produced by a process called melt spinning, so it is also known as melt-spun NdFeB powder or rapidly quenched NdFeB powder. In this process, an ingot of NdFeB alloy is melted by arc or induction melting, and the molten metal is then poured or ejected onto the surface of a water-cooled rotating rim. The alloy rapidly solidifies into a thin ribbon, typically about 35 μm thick and 1–3 mm wide.
By carefully adjusting process parameters such as metal flow rate and rim speed, the quench rate—and therefore the microstructure—can be controlled to achieve optimal magnetic properties. The solidified ribbon is then collected and milled into a flake-shaped powder, followed by a crystallization heat treatment to develop the desired magnetic performance of the isotropic NdFeB powder.
Isotropic NdFeB powder is mainly used to produce bonded Neodymium magnets. These magnets are composite materials made by mixing the powder with polymer binders and then forming it into finished parts by compression molding, injection molding, extrusion, or calendaring, with the magnetic particles dispersed throughout the binder matrix.
After forming, the parts are magnetized by applying an external magnetic field to give them permanent magnetic properties. Because isotropic NdFeB powder is magnetically isotropic, it allows great flexibility in magnetization direction and pattern. This makes it ideal for producing multipole ring magnets and other complex geometries widely used in motors and related applications.
