| Nanocrystalline composite NdFeB magnets consist of soft magnetic phase of high saturation magnetization and hard magnetic phase of high coercivity. These magnets produce much strong intergranular exchange coupling within nano-scale, thus resulting to high remanence and high energy product. So nanocrystalline magnets with low cost will have potential develop application prospect. In order to have a good understanding on relationships of heat treatment process and magnetic properties of nanocrystalline composite Nd2Fe14B/α-Fe magnets, effects of components and doped elements on magnetic properties and microstructure, nanocrystalline NdFeB magnetic powder was prepared by melt spun and crystallization treatment. Lots of experimental theoretic analysis had been carried out by use of modern instruments, such as optical microscopy, SEM, TEM, XRD,TMA,DSC.Firstly, effects of melt-spun and crystallization treatment process on magnetic properties had been investigated, in order to determine optimal process parameters. It was found that the optimal process is positive pressure +0.01MPa in Ar atmosphere, spinning speed 17m/s, crystallizing point 700 ℃ for 1525min for Nd10(FeCoZr)83.5B6.5 alloy. Magnetic properties with partially amorphous and crystallization treatment prefer to wholly amorphous. Level of amorphous under positive pressure is greater than negative pressure. There is an optimal parameter about crystallization time and temperature, such as time longer coercivity higher.Secondly, effects of component Nd and Co, and dopants, such as Zr, Dy, Nb, Ga and V on magnetic properties and microstructure had been studied. It is demonstrated that the best magnetic properties, Br=9.2kGs,Hcj = 10.12kOe,(BH)max=14.25MGOe, had been gotten at Nd10.5Fe80Zr3 0B6.5 alloy after optimal thermal treatment. The relative content of the 2:14:1 phase increases with the increase in the Nd content. This is beneficial to increase the coercivity Hcj, however a moderate Nd content is exist for the remanence and energy product. The crystallization point also arises along with the Nd content. Ferrite-magnetic exchange effect is enhanced and Curie temperature of magnets is increased as a result of Co replacing Fe atom. Zr dopants can significantlyimprove the magnetic properties and crystallization process of magnets. Zr dopants can delay precipitation growing of a-Fe phase, and so refine the grain. It is shown that partly Zr atoms are substituted for Nd atoms, thus increasing coercivity. Nb-dopants can greatly refine grains and improve magnetic properties. Dy-dopants can significantly increase coercivity.Lastly, effect of Nb and Zr additions on magnetic properties of (Nd0.4Pr0.6)8Fe87B5 melt-spun alloy had been studied. The combined Nb and Zr additions can promote forming amorphous phases, and increase crystallizing temperature and nucleation rate and thus refine grains.
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