DEVELOPMENT OF HIGH PERFORMANCE PERMANENT MAGNETS BASED ON Nd-Fe-B SYSTEM

Abstract

Rare earth iron boron magnets based on Nd 2 Fei.iB type is the most powerful permanent magnets, which have outstanding magnetic properties in the vicinity of room temperature. Production of NdFeB is carried out by two distinctly different processes. These include the conventional powder -sintering process and consolidation of rapidly solidified powders. The latter is used to produce both bonded and anisotropic bulk magnets. NdFeB sintered magnets essentially consist of three basic phases; Nd 2 FeuB (<t>), Nd|Fe 4 B4 phase (n.) and Nd-rich phase (n) Therefore, the magnetic properties of the magnets strongly depend on their microstructure. The current focus of NdFeB magnet research and development is on improvement of the magnetic properties such as the magnetic remanence (B r ) and intrinsic coercivity (He,), corrosion resistance and temperature characteristics of sintered magnets and rapidly solidified (melt spinning) magnets. Since the discovery of NdFeB magnets, their performance has been continuously enhanced and the current maximum energy product is achieved to be 444 ld/m 3 (55.8 MGOe). Other processes also have been used for improving microstructure for developing high energy product NdFeB magnets. These processes include: i) mechanical alloying process of metals which uses an inter-diffusional reaction magnet, ii) HDDR process (hydrogenation, disprorportionation, desorption, recombination) of magnet powder, and iii) nanocrystalline composite magnet (exchange-coupled) which are composed of magnetically hard and soft grains The negative side of the NdFeB magnet is their low corrosion resistance They are sensitive to attack by both climatic and corrosive environments, resulting in deterioration of the hard magnetic properties of the magnet In this paper the development of the high-energy product NdFeB based magnets in terms of improved microstructure and magnet processing methods is reviewed.

Research on MGT target location method based on rotating combined magnetic beacon

“…When the permanent magnet is uniformly magnetized in the axial direction, the demagnetizing field of the beacon becomes stronger as the dimension factors k = L/D increases resulting in the magnetic signal will decay faster, but too small will weaken the beacon's mechanical strength and shrink the service life [18]. When the magnet length exceeds 10 cm, the beacon is difficult to press and the mechanical strength is low, and when it reaches 25 cm, it is expensive and not suitable for general use [19]. When the magnetization directions of the permanent magnets are the same, a small-volume magnet unit can be combined shown in Figure 1, and the magnetic field generated by any volume of the magnet after the combination is almost equal to the magnetic field generated by a magnet of the same size.…”