Nd-Fe-B (neodymium-iron-boron) material was discovered in 1983 by physicists of United States and Japan. It is the strongest man-made permanent magnet so far. Nd-Fe-B material is mainly a type of intermetallic compound, Nd2Fe14B, which has a composition of two rare earth atoms, 14 iron atoms and one boron atom. Besides the main phase Nd2Fe14B in Nd-Fe-B material, there are small amounts of rare earth-rich phase (Nd-rich phase), boron-rich phase as well as other phases. The Nd-rich phase provides pinning of the domain walls so that Nd-Fe-B magnet has high coercive force. Today's commercial Nd-Fe-B magnets have many combinations of partial alloying substitutions for Nd and Fe, leading to a wide range of available properties. The rare earth content of Nd-Fe-B magnet alloys is typically 30 to 35 weight percent.
Today, due to its superior magnetic properties and reasonable costs, Nd-Fe-B permanent magnet has found its extensive application in many fields such as: computer devices, communication tools, motors, medical treatment instruments, sensors and speakers etc.
There are two families of Nd-Fe-B permanent magnets commercially available, that is, sintered and bonded magnet. Sintered Nd-Fe-B magnet is a fully densed and anisotropic material and provides the highest available magnetic energy products of any materials, ranging from 26 to 50 MGOe. While bonded Nd-Fe-B magnet is produced by bonding the rapidly quenched alloying powders with polymer bonders, and shows comparably low magnetic energy products. This is mainly because the commercially available bonded Nd-Fe-B magnet is isotropic on macroscopic magnetic properties and it is not a fully densed material. But isotropic bonded Nd-Fe-B magnet has its special advantages. For example, it can be fabricated by compression and injection molded processes and offers complex shapes with higher size-precision than sintered magnets. Moreover, unlike the anisotropic magnet that must be magnetically oriented in a preferred direction during the molding process, the isotropic bonded Nd-Fe-B magnet can be conveniently magnetized in any direction: axial, radial and multi-polar which implies complex magnetization capability over anisotropic magnets. Furthermore, isotropic bonded Nd-Fe-B magnet is made from rapidly quenched powders in which particles have fine microstructures and make it comparably stable in chemistry. We can also consolidate the rapidly quenched powders into a fully dense anisotropic magnet by plastic deformation to get high magnetic energy products comparable with sintered magnets.
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