Search

In this study, we aimed to enhance the quality of electrophoretic deposition (EPD) coatings for Nd-Fe-B grain boundary diffusion (GBD) by addressing issues related to the adhesion and densification of coating. We introduced a novel approach by incorporating polyvinyl pyrrolidone (PVP) into an alcohol suspension containing TbH3 nano-powders. The addition of PVP resulted in the formation of a dense coating with superior adhesion and a smooth surface. To evaluate the effectiveness of the EPD coating with PVP, we compared the EPD rate of the TbH3 nano-powders alcohol suspension with and without PVP. The EPD rate of the suspension with PVP exhibited a significant 30-fold increase compared to the suspension without PVP, indicating a substantial improvement in the electrophoretic efficiency. Based on our experimental findings, we recommend depositing the EPD coating at a voltage of 120 V and adjusting the deposition time accordingly to achieve a desired coating weight percentage of 1.0 wt% with a thickness of approximately 30 μm. Following the GBD process, the coercivity of the magnet with PVP increased from 1131 kA/m to 1896 kA/m, which improved the high-temperature stability of the magnet. Overall, our research offers a promising approach to overcome the limitations associated with EPD coatings for GBD applications, providing a potential solution for enhancing the performance and industrial viability of these coatings.

Sintered NdFeB magnets with different nano Al doping content were prepared by adding different nano A1 into NdFeB fine powder by intergranular doping method. The effects of nano Al doping on the microstructure, magnetic properties and temperature stability of sintered NdFeB magnets were systematically studied. Results show that the coercivity of the magnets can be significantly improved by doping nano Al. The coercivity increases from 8.91 kOe when undoped nano Al to 12.34 kOe when doped with 0.8% nano Al. However, the doping of nano Al can also reduce the remanence and magnetic energy product of the magnets. The doping of nano Al can improve the temperature stability of the magnets. Due to the low melting point of nano Al, doping nano Al can not only help the liquid phase sintering of sintered magnets and promote its densification, but also reduce the massive rare earth rich phases and increase the lamellar rare earth rich phases, which plays a demagnetizing coupling role and an important role in the magnetic hardening of sintered magnets. [ABSTRACT FROM AUTHOR]

In this paper, a corrosion-resistant glutamic acid (Glu)-Cu-Nano-Al2O3 composite coating with both hydrophobicity and self-healing characteristics was electrodeposited on the sintered Nd-Fe-B surface. The influence of the amount of Nano-Al2O3 added in the acidic Cu2+-glutamate (Glu2−) solution on the performance of the composite coating was studied, the results show that Nano-Al2O3 inclusion can make the surface of the composite coating appear papillary particles and make the composite coating hydrophobic. By analyzing the products of the composite coating after corrosion in 3.5% NaCl solution, it is shown that the codeposition copper dihydroglutamate (CuGlu2H2) and Glu particles in the composite coating are released and dissolved in the solution with pH = 6.5 after copper corrosion, and then complexed with Cu2+produced by corrosion to form an insoluble copper glutamate (CuGlu) passive film, which was deposited on the corroded coating to achieve self-repairing function and prevent further corrosion. The hydrophobicity and self-repairing function of the composite coating ensure that the sintered Nd-Fe-B has excellent corrosion resistance.

With the development of science and technology, the demand for high-performance sintered Nd-Fe-B magnets has increased dramatically. Since the grain refinement has a significant effect on the coercivity of sintered Nd-Fe-B magnets, a low-temperature sintering process using fine powder is proposed to control the grain size to improve the coercivity. Through this method, the grain size of the magnets is controlled to about 3.1 μm, which is smaller than the grain size of the conventionally processed magnet (4.2 μm). As a result, the intrinsic coercivity is increased by 1.24 kOe and the maximum magnetic energy product is increased by 1.23 MGOe, for the same composition. The influence of grain refinement on the magnet performance is studied in detail, which provides a guiding reference for the development of high-performance Nd-Fe-B sintered magnets. [ABSTRACT FROM AUTHOR]

Abstract Material properties of permanent magnet in the magnetic fluid seal are important factors that determine the sealing effect. However, the relationship between the magnetic properties of permanent magnet and the failure-pressure has not been studied quantitatively in the available research. In this work, the relationship between material properties of permanent magnet and the failure-pressure of magnetic fluid seal was obtained from theoretical analysis and numerical simulation. The permanent magnet was changed in materials to calculate the failure-pressures of a typical magnetic fluid seal. The results show that the failure pressure of the magnetic fluid seal increases with the increase of the maximum magnetic energy product of the permanent magnet, but there is a turning point. After that, the failure-pressure decreases as the maximum magnetic energy product increases.

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A systematic microstructure analysis has been carried out for the as-sintered and annealed Ti-doped sintered Nd-Fe-B magnets. Upon annealing, grain boundaries become more obvious and show higher Nd content and lower Fe content, leading to the improvement of coercivity. Meanwhile, the amount of Nd 6 Fe 13 Ga increases and that of Nd 2 Fe 14 B decreases, leading to a slight loss of remanence. Many rod-shaped TiB 2 precipitates are found both in the as-sintered and annealed samples with most of them located at grain boundaries. There is no significant difference between the as-sintered and annealed sample in the distribution, grain shape and size of TiB 2. Atomic-scale characterization of TiB 2 and its neighboring area reveals the existence of an amorphous layer surrounding TiB 2 with the thickness of 3.5 ± 2.5 nm. The amorphous layer is measured and analyzed to be non-ferromagnetic with obvious enrichment of Nd and Pr. Its existence is speculated to be the result of strong cohesion of Ti and B, leaving a B-poor region around TiB 2 difficult to form stable crystals. The existence of TiB 2 and the surrounding (Nd,Pr)-rich amorphous layer in the Ti-doped magnets is beneficial for preventing the propagation of reversed magnetic domains and improving coercivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The efficient regeneration of rare earth secondary resources of sintered Nd-Fe-B is of great significance for the recycling economy of rare earth resources. Since the mechanical properties of recycled magnets have a crucial impact on promoting its commercial application, tensile strength, compressive strength, hardness and fracture toughness of the original sintered Nd-Fe-B magnet and the recycled magnet were systematically studied and the mechanism was illustrated based on the analysis of the chemical composition and microstructure. The main fracture mechanism of recycled sintered magnets is intergranular fracture. The fracture toughness of recycled sintered magnets is slightly higher than that of original magnets, but the bending, compressive and hardness of recycled sintered magnets are slightly lower than that of original magnets. The differences in mechanical properties are mainly attributed to the higher content of rare earth and grain boundary phases in recycled magnets. In summary, the regenerated magnet has the similar mechanical properties as those of the original magnet, which can fully meet the requirements of the product. • The comprehensive mechanical properties of recycled magnets were studied. • The anisotropy of mechanical properties of recycled magnets was found. • The reasons of mechanical properties anisotropy were revealed. [ABSTRACT FROM AUTHOR]

In order to improve the magnetic properties and corrosion resistance of sintered Nd-Fe-B magnets, the (PrNd) 29.9 Dy 0.1 B 1 Co 1 Cu 0.15 Fe bal (wt%) powders were mixed with Mg nanopowders, as grain boundary modifiers. For Nd-Fe-B magnets with 0.1–0.4 wt% Mg addition, the result showed that addition amount of 0.1 wt% Mg, H cj reaches the maximum value of 999.1 kA/m, Br reaches 1.436T, (BH) max reaches 396.9 kJ/m 3 and magnet density is 7.42 g/cm 3 , which are related to the microstructural modification of grain boundaries and the magnet density. Effects of Mg addition on corrosion behavior in sulphuric acid and sodium chloride solution were researched by electrochemical workstation. With increase of Mg addition level, the magnet turns to have a higher corrosion potential and lower corrosion current density, the corrosion poverty is improved. However, temperature coefficient remained nearly unchanged with Mg addition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bilayer Al/Cr films were prepared on Nd-Fe-B magnets by magnetron sputtering. • Sputtering power allowed to vary morphology and properties of Al/Cr films. • Thin Al/Cr film improved anti-corrosion and mechanical properties of Nd-Fe-B. • Magnetic properties were not deteriorated with Al/Cr film deposition. Corrosion induced irredeemable magnetic loss of Nd-Fe-B permanent magnets is of great concern in industrial applications. Surface coating treatment provides an effective approach for improving corrosion resistance, but the coating induced magnetic strength deterioration should also be taken into account, in addition to the pursuing of anti-corrosion performance. Herein, bilayer thin Al/Cr films were prepared on Nd-Fe-B magnets, the corrosion behavior and mechanical properties of Nd-Fe-B were investigated. The results revealed that Al/Cr film with 510 nm thickness provided the best anti-corrosion performance in 3.5 wt% NaCl solution, offering a corrosion current density of 2.08 × 10-7 A/cm2 which was two orders of magnitude lower than that of bare Nd-Fe-B magnets. Bilayer structured Al/Cr film with Cr 2 O 3 passivation layer can effectively prevent the penetration of the corrosive ions. In addition, deposition of Al/Cr film on Nd-Fe-B magnets gave no significant impact on the magnetic properties, furthermore, the hardness and Young's modulus were both improved. The present work demonstrated that Al/Cr films have great potential to be utilized for providing effective corrosion and mechanical protections for Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]

In this work, a double coating protection technique of phosphating treatment and copper plating was made to improve the corrosion resistance of sintered Nd–Fe–B magnets. In other words, the intergranular region of sintered Nd–Fe–B is allowed to generate passive phosphate conversion coating through phosphating treatment, followed by the copper coating on the surface of sintered Nd–Fe–B. The morphology and corrosion resistance of the phosphated sintered Nd–Fe–B were observed using SEM and electrochemical method respectively. The phosphate conversion coating was formed more preferably on the intergranular region of sintered Nd–Fe–B than on the main crystal region; just after a short time of phosphating treatment, the intergranular region of sintered Nd–Fe–B has been covered by the phosphate conversion coating and the corrosion resistance is significantly improved. With the synergistic protection of the intergranular phosphorization and the followed copper electrodeposition, the corrosion resistance of the sintered Nd–Fe–B is significantly better than that with a single phosphate film or single plating protection. [ABSTRACT FROM AUTHOR]

Abstract: A novel grain boundary diffusion (GBD) treatment with a Dy–Ni–Al eutectic alloy powder allowed Dy to penetrate into sintered plates of Nd–Fe–B magnet as thick as 5mm. The coercivity of the magnet was increased from a value of 1160kA/m (14.5kOe) to 1760kA/m (22kOe). This was achieved without any marked decrease in remanance and with a high squareness. [ABSTRACT FROM AUTHOR]

Abstract: Effects of the dehydrogenation of the hydrogen decrepitated (HD) powders on the magnetic properties and the fracture strength of sintered NdFeB magnets were studied. It was found that the lattice parameters and the crystal phase of NdFeB changed significantly with the various hydrogen contents of the resultant HD powders due to the different degrees of dehydrogenation. The magnetic properties and fracture strength increased with decreasing hydrogen content, reaching the maximum increases of 200% for both intrinsic coercivity and bending strength, which can be ascribed to the improved microstructure of the sintered NdFeB magnets. The hydrogen remaining in the HD powders diffused out and affected drastically the grain and grain boundaries by the hydrogen out-take channel during the subsequent sintering process. [Copyright &y& Elsevier]

Abstract: The effect of annealing treatment on the magnetic properties and microstructure of Nd12.0Dy2.8Fe74.7Co3.4Cu0.2B6.9 magnets has been investigated. It is found that intrinsic coercivity i H c is improved with the increase of annealing temperature, and the maximum value is attained at 480°C. i H c is rapidly decreased with a further increase of annealing temperature. For a given annealing temperature of 480°C, i H c is increased with the increase of annealing time, and the maximum value is achieved at 2h. It almost remains constant when annealing time is further increased. However, while the annealing treatment has little effect on remanence B r. It is certain that the increase of i H c for the annealed magnets arises from the more smooth grain boundaries of the RE2Fe14B phases and the more continuous/uniform distribution of RE-rich phases. The great change of microstructure in the annealed magnets can be explained using atomic diffusion theory. [Copyright &y& Elsevier]

The effect of boron variation in the minor addition of grain-boundary alloys on the mechanical properties and microstructure of sintered Nd–Fe–B magnets has been studied. It shows that the bending strength of most magnets with minor grain-boundary alloy additions is much higher than that of the magnet prepared by the single alloy. The maximum of the former reached 397 MPa, which was higher than the bending strength of cast/hot-rolled magnets. The latter was only 309 MPa. Minor additions of the grain-boundary alloys made the distribution of grain-boundary phase more uniform so that the phenomena of the direct contacts between main-phase grains nearly disappeared. The irregular grain growth was restrained. This is also one of the reasons that the magnets with minor grain-boundary alloy additions have possessed higher bending strength. In addition, the phase analyses indicated that the reduction of crystal structure anisotropy probably helps to increase bending strength. The study results also show that minor additions of the grain-boundary alloys do not almost affect the magnetic properties of sintered Nd–Fe–B magnets. It suggests that slightly adding grain-boundary alloys and properly adjusting its composition can substantially increase the bending strength of sintered Nd–Fe–B magnets without a sacrifice of magnetic properties. [Copyright &y& Elsevier]