Abstract
Permanent magnets, and particularly rare earth magnets such as Nd-Fe-B, have attracted much attention because of their magnetic properties. There are two well-established techniques for obtaining sintered magnets and bonded Nd-Fe-B magnets. Powder metallurgy is used to obtain high-performance anisotropic sintered magnets. To produce bonded magnets, either melt-spinning or the hydrogenation, disproportionation, desorption, and recombination process is used to produce magnet powders, which are then mixed with binders. Since the development of Nd-Fe-B magnets, several kinds of intermetallic compounds have been reported, such as Sm2Fe17Nx and Sm(Fe,M)12 (M: Ti, V, etc.). However, it is difficult to apply a liquid-phase sintering process similar to the one used for Nd-Fe-B sintered magnets in order to produce high-performance Sm-Fe–based sintered magnets because of the low decomposition temperature of the compound and the lack of a liquid grain boundary phase like that in the Nd-Fe-B system. Therefore, bonded magnets are useful in the production of bulk magnets using these Sm-Fe based compounds. This article reviews recent progress in our work on the development of high-performance bonded magnets using Nd2Fe14B and Sm2Fe17Nx compounds.
Highlights
Permanent magnets are an essential material in many fields of technology because of their ability to provide magnetic flux and have found applications in a wide range of devices
This review focuses on bonded magnets, high-performance R-Fe (R: rare earth) bonded magnets, and summarizes recent research related to the anisotropy mechanism of the HDDR process for high-performance Nd-Fe-B resin-bonded magnets, as well as the develop ment of high-performance Sm2Fe17Nx metal-bonded magnets using a low-melting-point alloy such as Zn
This indicates that hydrogen pressure and temperature conditions close to the equi librium curve of the hydrogena tion disproportionation (HD) and desorption recombina tion (DR) reactions in the pressure-temperature diagram together with the resultant reaction rate are preferred for obtaining higher anisotropy [22]
Summary
Permanent magnets are an essential material in many fields of technology because of their ability to provide magnetic flux and have found applications in a wide range of devices. The anisotropic Nd-Fe-B magnet powders prepared by HDDR process are used for obtaining anisotropic bonded magnets in today. The nitrogen is thought to occupy three 9e octahedral interstitial sites around the Sm atoms in the Sm2Fe17 compound with the rhombohedral (Th2Zn17) struc ture. The production process for bulk magnets using this com pound is restricted to bonded magnets mixed with resin or low melting point metals. This review focuses on bonded magnets, high-performance R-Fe (R: rare earth) bonded magnets, and summarizes recent research related to the anisotropy mechanism of the HDDR process for high-performance Nd-Fe-B resin-bonded magnets, as well as the develop ment of high-performance Sm2Fe17Nx metal-bonded magnets using a low-melting-point alloy such as Zn. 2. High-performance Nd-Fe-B bonded magnets obtained by hydrogenation, disproportionation, desorption, and recombination
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