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• Nanocomposite PrNd-Fe-B/Alnico are fabricated. • A special microstructure with the Alnico phase dispersed within the NdPrFeB phase results in excellent magnetic properties. • The Curie temperature of the composite alloys is enhanced from 570 K to 643 K by adding 25% low-grade Alnico. • The maximum energy product is enhanced from 110 kJ/m3 to 133 kJ/m3. NdFeB-based permanent magnets have the highest maximum energy products, but their low Curie temperatures limit their applications. Alnico permanent magnets have relatively modest magnetic energy products, but have very high Curie and working temperatures. In this manuscript, we report new NdPrFeB/Alnico nanocomposite magnetic materials with enhanced Curie temperatures and maximum magnetic energy products. A special microstructure with the Alnico phase dispersed within the NdPrFeB phase results in excellent magnetic properties. The Curie temperature of the composite alloys is enhanced from 570 K to 643 K by adding 25% low-grade Alnico. The enhanced Curie temperature which results from the cobalt and nickel replacement for iron in the 2:14:1 phase, and the molecular field penetration improves the temperature stability of the magnets. The beneficial heterogeneous distribution of the constituent phases and elements was confirmed by transmission electron microscopy and electron diffraction spectroscopy analyses. The maximum energy product is enhanced from 110 kJ/m3 to 133 kJ/m3. Magnetostatic interaction and exchange interaction in the alloys were studied by means of Henkel plots and minor hysteresis loop measurements. Despite the high content of the Alnico phase with relatively large special dimensions, there were no kinks in the demagnetization curves either at 300 K or 400 K. Furthermore, no kink was noted at low and high applied fields in the demagnetization-magnetization process which shows the effective magnetic interactions. This work would elucidate the development of nanocomposite magnetic material with high energy product without the use of heavy rare earths and with the economical use of Nd and Pr. [ABSTRACT FROM AUTHOR]

Four kinds of coarse Nd–Dy–Fe–B powder were oxidized at room temperature in air and in a dryer, which were dehydrogenated at different temperatures in vacuum after hydrogen decrepitation (HD). The oxidation and water absorption of these coarse powders were investigated by a weight change method. It was found that the undegassed powder had a higher oxidation rate, as well as higher water absorption, than the dehydrogenated powder, especially in the first stage of oxidation. The higher oxidation resistance of degassed powder results from the lower hydrogen concentration and smaller amounts of hydrides. So, the mechanisms of hydrogen accelerating the oxidation probably focus on that hydrogen bonds between hydrides in powder and water molecules in air accelerate the absorption of water from ambient air, which speeds the electrochemical reaction in the powder; and that defects caused by hydrogen in powder induce oxygen diffusion more quickly. [Copyright &y& Elsevier]

Summary This paper reports, for the first time, the use of electron backscattered diffraction (EBSD) to study orientation in sintered NdFeB type magnets. The magnetic properties of NdFeB magnets are greatly improved if a strong crystallographic texture is firstly achieved, namely, the direction of the c-axis is along the direction of magnetization. A systematic survey of sample preparation techniques showed that samples that were mechanically polished and then etched gave the most reliable EBSD data. Analyses were made using both fully automated EBSD scans and by EBSD measurements taken after manual movement of the beam. The EBSD results are presented as secondary electron SEM micrographs, orientation images and 001 pole figures. For the selection of grains investigated, the deviation of the c-axis was shown to be between 10° and 30° from the ideal [001]//magnetization direction. It is demonstrated that EBSD is a valuable tool for characterizing the microstructure and texture relationships and for assessing the performance of the processing routes of NdFeB magnets. [ABSTRACT FROM AUTHOR]

• Hf has been added into NdFeB ribbons alloys with different Nd content. • The addition of Hf on NdFeB alloys with different Nd content show different effects. • For 27 wt% Nd content the addition of Hf improved the intrinsic coercivity. • For 29 wt%, 31 wt% the addition of Hf enhances the remanence and energy density. • Hf partially entered into the main phase and exhibited great grain refinement effects. In this paper, the effects of Hf addition on phase composition, Curie temperature, exchange coupling effect, coercivity mechanism, room temperature magnetic properties, high temperature magnetic properties and thermal stability of NdFeB alloys with different Nd content (27–31 wt%) are systematically studied. Hf addition showed different effects on the magnetic properties of NdFeB alloys at different Nd contents and different test temperatures. At 300 K, the intrinsic coercivity is increased with low Nd content (27 wt%), while the remanence and the maximum magnetic energy product are significantly improved with higher Nd content (29 wt%, 31 wt%). At 398 K, the intrinsic coercivity, the remanence, the maximum magnetic energy product and the temperature stability improved in NdFeB alloys with high Nd content (29 wt%, 31 wt%). [ABSTRACT FROM AUTHOR]