Nd2Fe14B Phase Research Articles

Microstructure and Magnetic Properties of NdFeB Sintered Magnets Diffusion-Treated with Cu/Al Mixed Dyco Alloy-Powder

AbstractWe investigated the microstructural and magnetic property changes of DyCo, Cu + DyCo, and Al + DyCo diffusion-treated NdFeB sintered magnets. The coercivity of all diffusion treated magnet was increased at 880ºC of 1stpost annealing(PA), by 6.1 kOe in Cu and 7.0 kOe in Al mixed DyCo coated magnets, whereas this increment was found to be relatively low (3.9 kOe) in the magnet coated with DyCo only. The diffusivity and diffusion depth of Dy were increased in those magnets which were treated with Cu or Al mixed DyCo, mainly due to comparatively easy diffusion path provided by Cu and Al because of their solubility with Ndrich grain boundary phase. The formation of Cu/Al-rich grain boundary phase might have enhanced the diffusivity of Dy-atoms. Moreover, relatively a large number of Dy atoms reached into the magnet and mostly segregated at the interface of Nd2Fe14B and grain boundary phases covering Nd2Fe14B grains so that the core-shell type structures were developed. The formation of highly anisotropic (Nd, Dy)2Fe14B phase layer, which acted as the shell in the core-shell type structure so as to prevent the reverse domain movement, was the cause of enhancing the coercivity of diffusion treated NdFeB magnets. Segregation of cobalt in Nd-rich TJP followed by the formation of Co-rich phase was beneficial for the coercivity enhancement, resulting in the stabilization of the metastable c-Nd2O3phase.

Notice of Removal: Micromagnetic Study for Magnetic Properties of Exchange-Coupled Nanocomposite Magnetic Systems With $\alpha$ -Fe Grains Embedded in Nd2Fe14B Matrix

In this paper, the relationship between the magnetic properties and microstructures of nanocomposite isotropic exchange-coupled systems with the structure of α-Fe crystalline grains embedded in Nd 2 Fe 14 B matrices has been estimated by micromagnetic finite-element method. And then, the results have been analyzed by means of the effectiveness of exchange coupling between the magnetically hard Nd 2 Fe 14 B and soft α-Fe phase of the exchange-coupled Nd 2 Fe 14 B/α-Fe magnetic systems. The effectiveness of interphase exchange coupling has been estimated by the volume fractions of exchange coupling area near phase boundaries between α-Fe grains and Nd 2 Fe 14 B matrix. The results have shown the micromagnetic mechanism of the advanced magnetic properties of the exchange coupled magnetic systems with the structure of α-Fe grains embedded in Nd 2 Fe 14 B matrix. In addition, the optimal magnetic properties can be expected in the case of comparatively the large grain sizes of α-Fe and Nd 2 Fe 14 B phase due to the characteristic structure of those magnetic systems.

Boundary structure modification and magnetic properties of Nd-Fe-B sintered magnets by co-doping with Dy2O3/S powders

In this paper, the effect of Dy2O3/S co-doping on the magnetic properties and microstructure was studied in Nd-Fe-B sintered magnets. With S co-doping, the coercivity increased due to grain boundary modification and Dy selective introduction. Continuous grain boundary phases were formed in the co-doped magnets with smaller grain size. The average grain size after a doping of 0.2wt% S is 7.25µm, which is approximately 2.37µm smaller than that of the S-free sintered magnets(9.62µm). The coercivity of the Dy2O3/0.2wt% S co-doped magnets could be increased from 20.9 to 22.8kOe with changing the remanence and the maximum magnetic energy product slightly. S precipitates in the Nd-rich phases were hexagonal Nd2O2S phase. Dy avoided the Nd2O2S phase in the triple junction region, resulting in more available Dy atoms diffusing into the Nd2Fe14B phase grains to enhance the anisotropy field. Dy-saving was achieved by forming Nd2O2S phase in the Dy2O3/S co-doped magnets.

A nanocomposite structure in directly cast NdFeB based alloy with low Nd content for potential anisotropic permanent magnets

The magnetic properties of NdFeB magnets can be tailored with different kinds of microstructures. In this work, a nanocomposite structure with amorphous phase remaining inside the micro-sized Nd2Fe14B type grains was observed by Scanning and Transmission Electron Microscopy on the suction cast Nd11Fe60Co10Ti2.5Nb0.5C0.5B15.5 alloy, and then confirmed by various characterization techniques. The worm-like soft magnetic amorphous phases show strong exchange coupling with Nd2Fe14B phase. As a result, the open recoil loops, which are typical characteristics for nanocomposite alloys consisting of hard and soft magnetic phases, have been clearly evidenced. Thus, the formation of this structure may provide an alternative approach to design and fabricate anisotropic nanocomposite NdFeB-based permanent magnets with enhanced magnetic properties.

Phase-structural state diagrams and hysteresis properties of rapidly solidified alloy Nd 10.4 Zr 4.0 Fe 75.1 Co 4.1 B 6.4 after heat treatment

Abstract This paper investigates complex studies of phase composition, thin crystalline structure parameters and magnetic properties of rapidly solidified alloy powders Nd10.4Zr4.0Fe75.1Co4.1B6.4 in initial state and after heat treatments in the temperature range 380–700 °C for 30, 60 and 120 min. The research shows that there is a hard magnetic phase Nd2Fe14B and soft magnetic phases α-Fe and Nd2Fe17 in the structure of the investigated as-solidified alloy. And low-magnetic properties (Hci = 186 kA/m) are due to the presence of the Nd2Fe17 phase. After heat treatments in the temperature range 520–550 °C coercivity of the powders grow up to Hci ≈ 750 kA/m. However, after annealing at the temperatures higher than 600 °C, coercivity drastically drops due to the phase transformation of a hard magnetic phase Nd2Fe14B and the average grain growth, with the phase transforming into a soft magnetic phase Nd2Fe17.

Characteristics of Nd-Fe-B Permanent Magnets Present in Electronic Components

The increasing use of rare earths elements (REEs) in a number of recent technological innovations led to a rapid increase (>50% in the last decade) in their applications. Europe is one of the most important regions of consumption of these substances. In this context, Europe in its 'Raw materials' strategy puts the recycling at the center of its concerns to provide a part of securing its supplies in REEs. Recycling of these substances, on an industrial scale, remains somewhat developed while it presents numerous advantages over the exploitation of primary resources. This paper will present some results obtained from characterization study of permanent magnets (PMs) present in WEEEs. Three components containing PMs are identified: hard disk drives, small electric motors and speakers. The representative sample of these components has been dismantled manually to recover the PMs contained and to quantify their amount. The results show that the weight percentage of the PMs varies from 4 to 6% in the speakers, 2.5 to 2.8% in the hard disks, and between 0.8 and 2% in some electric motors. The results of the thermal treatment of the Nd-Fe-B PMs of the investigated samples show that the majority of these PMs lose their magnetic property upon reaching Curie temperature (300-400°C) in 15-20 min. Scanning Electronic Microscopy reveals the morphological aspects of the PM which consist in crystals shaped tetrahedral phase Nd2Fe14B sintered in the presence of the interphase rich in Nd, Dy and Pr. The PM are layer coated with 20 μm thick, consisting of Ni, Zn or metals alloys.

Coercivity of Nd-Fe-B hot-deformed magnets produced by the spark plasma sintering method

The effects of Nd-Cu alloy powder addition on the microstructures and magnetic properties of Nd-Fe-B hot-deformed magnets produced by the spark plasma sintering (SPS) method were investigated. The addition of a small amount of Nd-Cu alloy powder, up to 2%, significantly increased the coercivity of the Nd-Fe-B hot-deformed magnets without deteriorating the crystallographic alignment of the Nd2Fe14B phase. The Nd-Fe-B hot-deformed magnet with 2% Nd-Cu alloy powder had the same remanence value as the Nd-Fe-B hot-deformed magnet without Nd-Cu alloy powder addition, but the magnet with 2% Nd-Cu alloy powder exhibited higher coercivity and a higher maximum energy product than the magnet without Nd-Cu alloy powder addition.

Influence of microstructure on the interphase exchange coupling of Nd2Fe14B + 10 wt%α-Fe nanocomposites obtained at different milling energies

The influence of the microstructure on the magnetic interphase exchange coupling of Nd2Fe14B + 10 wt% α-Fe nanocomposites obtained through mechanical milling was studied as a function of the milling energy (shock, friction and the ball impact energy) by varying only the size of the grinding media (steel balls with diameters of 5, 10, 15, and 20 mm). The mean crystallite sizes in both Nd2Fe14B and α-Fe were studied through X-ray diffraction, by the Scherrer method. The variation in milling energy had little impact on the mean crystallite sizes for α-Fe; approximately 10 nm after annealing at 700 °C for 1.5 min and 20 nm after annealing at 800 °C for 1.5 min. However, after annealing, the Nd2Fe14B crystallites present average sizes ranging from 50 nm (for the lowest impact energy used) to 20 nm (for high impact energy), with no significant variation of the grain sizes due to annealing temperature in the investigate range. Increasing the milling energy does not lower the mean crystallite size beyond 20 nm for the hard magnetic phase. The influence of the microstructure on the magnetic interphase exchange coupling between the hard and soft magnetic phases is reflected in the demagnetization curves and dM/dH vs. H plots for the annealed samples. The samples in which the Nd2Fe14B phase presents lower mean crystallite sizes show an improvement in both coercivity and energy product over the samples with larger grains. Further improvement in the magnetic interphase coupling can be observed as the average crystallite sizes decrease to 20 nm, for which the highest values for Hc = 0.65 T and (BH)max = 110 kJ/m3 were recorded.

Crystal structure and magnetic properties of Nd2Fe14B powder prepared by using high energy milling from elements metal Nd,Fe,B powders

The Nd2Fe14B powder has been made by using High Energy Milling (HEM) from mixed metal powders Iron (Fe), Neodymium (Nd) and Boron (B). The Nd, Fe and B powders were mixed according stoichiometric composition (atomic ratio Nd:Fe:B = 2: 14: 1) and milled and milling time was varied in 10, 20, and 40 hours by using HEM. Toluene liquid was used as milling media to protect of metal powders from oxygen. The measurement result of x- ray diffraction show that the optimum Nd2Fe14B phase already formed about 69,46% after milling 40 hours with crystallite size about 25.64 nm. The magnetic properties of milled powders were measured by using VSM at room temperature. The highest value of magnetic properties are obtained at powder milled in 40 hours, at this condition, it is obtained Ms = 122 emu/g, Mr = 81 emu/g, Hc = 5.54 kOe and BHmax = 11.01 MGOe.

Tuning the microstructure and magnetic properties of bulk nanocomposite magnets with large strain deformation

In this study, we investigated the effect of strain on the microstructure and magnetic properties of bulk α-Fe/Nd2Fe14B nanocomposite magnets produced by a combination of severe plastic deformation at room temperature and subsequent thermal annealing. Experiment results indicate that severe plastic deformation can induce the formation of α-Fe and Nd2Fe14B nanocrystals in the amorphous matrix and then suppress the formation of metastable intermediate phases during thermal annealing. The volume fraction of α-Fe phase in the magnets increases as the strain increases，and the grain size of α-Fe and Nd2Fe14B phases significantly decreases. As a result, the bulk magnets made at ε=6.2 show enhanced magnetic properties, (BH)max=17.8 MGOe and Hc=7.2kOe, compared with that of directly annealed partially amorphous (Nd-Pr)-Fe-Co-Nb-B, (BH)max=12.2 MGOe and Hc=6.2kOe.

An Innovative Process Using Only Water and Sodium Chloride for Recovering Rare Earth Elements from Nd–Fe–B Permanent Magnets Found in the Waste of Electrical and Electronic Equipment

We developed a new and environmentally friendly approach for recycling Ni–Cu-coated Nd–Fe–B permanent magnets included in computer hard disk drives collected as the waste of electrical and electronic equipment (WEEE). In a closed reactor, the coated magnets are heated at 250 °C in water mixed with sodium chloride for up to 18 h. First, the hydrothermal treatment induces the removal of the metallic coating that can be recovered by sieving. Then, the Nd-rich phase reacts with water, leading to the formation of Nd(OH)3. Atomic hydrogen is absorbed by the Nd2Fe14B phase, leading to the formation of Nd2Fe14BHx. The volume expansion of the intergranular phase, in relation to the formation of Nd(OH)3, together with the lattice expansion of the Nd2Fe14BHx phase causes the disintegration of the magnets. Finally, Nd2Fe14BHx is oxidized by water into Fe3O4 and Nd(OH)3. The Nd(OH)3 crystals can be isolated from the Fe3O4 crystals by magnetic separation. This process is thus an easy way to extract rare earths from permanent magnets found in WEEE. It uses green chemistry design principles and can be applied to large amounts of magnetic wastes.

Effect of element substitution on nanostructure and hard magnetism of rapidly quenched Nd2Fe14B

The structural and magnetic properties of Nd12Fe82B6 and Nd10M2Fe82B6 (M = Nb, Ti, Zr, Cr) alloys prepared using arc melting and melt spinning have been investigated. All the samples are found to crystallise with a tetragonal Nd2Fe14B phase without any alloy or elemental impurities. There is a small decrease in the unit cell volume of Nd2Fe14B due to transition metal (M) addition. The substitution of Nb and Ti refines and homogenises the nanostructure of the alloys, promoting intergrain exchange coupling leading to an increase in the remanence and energy product. For example, the remanence and energy product of Nd12Fe82B6 and Nd10Nb2Fe82B6 are 8.4 kG and 15 MGOe, and 9.9 kG and 20 MGOe, respectively. The J(T) curves are similar to those of a single phase ferromagnetic material suggesting no segregation of ferromagnetic impurities. The observed structural and magnetic properties are consistent with the fact that the substitutional transition metal atoms occupy the Nd site of the tetragonal Nd2Fe14B crystal lattice. The improvement of magnetic properties of nanocrystalline Nd2Fe14B alloys with the decrease in Nd concentration may be beneficial for the application of this material in bonded magnets.

Sinthesis and Characterization of Nd<sub>2</sub>Fe<sub>14</sub>B Powder from Nd-Fe-B Flakes by Wet Mechanical Milling and Heat Treatment

The Nyodimium-Iron-Boron (Nd-Fe-B) based materials are known as the best type of magnetic materials and it contains a magnetic phase Nd2Fe14B. The Nd-Fe-B alloy Flakes is one of the main raw material for producing of NdFeB-based permanent magnets and the size of Nd-Fe-B flakes are still coarse. Synthesis of Nd2Fe14B powder has been done by a wet mechanical milling method using the High Energy Milling (HEM) for 10 hrs and continued by heating at 600°C in vacuum condition (10-4 Pa). This process is used to produce a fine powder Nd2Fe14B for making of permanent magnets. The milling medium was used a toluene (pa-Emerck)) to protect of particle from oxidation during the milling process. After milling processes, the samples were measured distribution particle size by using Particle Size Analyzer (PSA). Microstructure analysis has been conducted by using X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM/EDX) for samples before milling and sample after heating. The characterization results show that after milling 10 hours, it was obtained fine powder with average size about 1.35 μm. According to SEM/EDX and XRD analysis show that the crystal structure of the sample before milling was different compared to the sample after heating. It is found new magnetic phase with formula Nd2Fe14B.

Enhancement of magnetic properties by Zn addition in Nd-Fe-B hot-deformed magnets produced by spark plasma sintering method

Nd-Fe-B hot-deformed magnets with Zn addition were prepared from Nd-Fe-B hot-pressed magnets by the spark plasma sintering (SPS) method. The microstructures and magnetic properties of the resultant Nd-Fe-B hot-deformed magnets were investigated. The Nd-Fe-B hot-deformed magnet without Zn addition had the crystallographic alignment of the Nd2Fe14B phase and was magnetically anisotropic, but showed a relatively low coercivity value. It was found that the addition of a small amount of Zn increased the coercivity of the Nd-Fe-B hot-deformed magnets without deteriorating the crystallographic alignment of the Nd2Fe14B phase. The Nd-Fe-B hot-deformed magnet with 1%Zn had fine Nd2Fe14B grains and exhibited a high coercivity of 0.97 MA m−1 with a maximum energy product of 312 kJ m−3.

Coercivity Mechanism in Nd-Fe-B Nanoparticles Synthesized by Reduction-Diffusion Process

Nd-Fe-B gel was prepared by employing the precursors of chloride-based metal salts including NdCl3⋅6H2O, FeCl3⋅6H2O, H3BO3, citric acid, and ethylene glycol. Mixed oxide powders were fabricated by subsequent annealing. The oxide powders were reduced at 800 °C in Ar + H2 atmosphere for different times (2, 5, 10, 15, and 24 h) to prepare Nd2Fe14B nanoparticles. The role of reduction time in phase, morphologies, microstructure, and magnetic properties of the final powders was investigated by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM) techniques, respectively. The results show that the Nd2Fe14B phase was formed successfully at higher reduction times (15 and 24 h), and the average size of reduction-treated products was less than 220 nm. The magnetic properties were fluctuated with an increase in reduction time at a reduction temperature of 800 °C. The samples reduced for 15 h had a maximum coercivity of 1873 Oe, and the samples reduced for 24 h had a maximum saturation magnetization of 118.52 emu/g. A maximum squareness ratio of 0.64 was obtained by reduction for 24 h. The results show that the reduction-diffusion process at 800 °C was done successfully in higher reduction times.

Anisotropic diffusion mechanism in grain boundary diffusion processed Nd–Fe–B sintered magnet

We investigated the anisotropic diffusion mechanism of Dy in a DyH2 dip-coated magnet in terms of both the crystal orientation of the Nd2Fe14B phase and the aligned direction of the magnet. A Dy-rich shell was formed preferentially at the interface, which is parallel to the [001] axis (c-axis) of the Nd2Fe14B crystal, during the grain boundary diffusion process (GBDP) because lattice diffusion of Dy perpendicular to the c-axis of the Nd2Fe14B crystal is much easier than that parallel to the c-axis. In contrast, the grain boundary diffusion depth in the direction perpendicular to the aligned direction (c-axis) of the magnet was much shorter (∼100 μm) than that in the direction parallel to the aligned direction (∼250 μm). Anisotropic grain boundary diffusion depending on the aligned direction of the magnet was not the result of the anisotropic Nd-rich grain boundary phase distribution but of anisotropic lattice diffusion depending on the Nd2Fe14B crystal orientation. Increasing the ratio of the surface areas perpendicular and parallel to the aligned direction (c-axis) of the magnet is expected to further improve the coercivity of the GBDP magnet.

On the Magnetic and Structural Properties of Neodymium Iron Boron Nanoparticles

Neodymium iron boron nanoparticles were synthesized by means of sol–gel method. Correlation between magnetic properties and structural features were evaluated. The Nd–Fe–B gel was formed in hydrogen atmosphere. The gel was subsequently annealed under vacuum condition to obtain Nd–Fe–B oxide phases. The oxides powders were reduced at different temperatures of 750, 775, 800, 825, 850, and 875 ∘C for 3 h in a mixture of Ar and H2 atmosphere to prepare Nd2Fe14B nanoparticles. The role of reduction temperature on phase, morphologies, microstructure, and magnetic properties of the final powders was investigated by employing X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), and vibrating sample magnetometer (VSM), respectively. The results show that Nd2Fe14B phase was formed successfully at temperatures of 750–875 ∘C. Maximum coercivity of 1757 Oe was obtained at 875 ∘C. The variation of coercivity was described by considering the particle size and magnetocrystalline anisotropy constant.

Observation of Pseudopartial Grain Boundary Wetting in the NdFeB-Based Alloy

The NdFeB-based alloys were invented in 1980s and remain the best-known hard magnetic alloys. In order to reach the optimum magnetic properties, the grains of hard magnetic Nd2Fe14B phase have to be isolated from one another by the (possibly thin) layers of a non-ferromagnetic Nd-rich phase. In this work, we observe that the few-nanometer-thin layers of the Nd-rich phase appear between Nd2Fe14B grains due to the pseudopartial grain boundary (GB) wetting. Namely, some Nd2Fe14B/Nd2Fe14B GBs are not completely wetted by the Nd-rich melt and have the high contact angle with the liquid phase and, nevertheless, contain the 2-4-nm-thin uniform Nd-rich layer.

Effect of desorption and recombination on texture development in hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B magnets

The microstructural evolution of Nd–Fe–B magnets during a hydrogenation–disproportionation–desorption–recombination (HDDR) process was investigated, with particular focus on the effects of the desorption–recombination (DR) stage of the process. Samples that went through the DR process under different conditions were compared to examine the texture development during the reaction. Even though the same hydrogenation–disproportionation (HD) treatment was carried out on all samples before the DR reaction, variations in conditions of the latter significantly affected the development of texture in the samples. In consideration of the microstructural evolution, magnetic properties, and thermodynamics, nucleation of recombined Nd2Fe14B grains was found to occur not only at the NdH2/Fe2B interfaces but also at the NdH2/α-Fe interfaces, and it was affected by the desorption of hydrogen. Preferential growth of nuclei at the NdH2/Fe2B interfaces, which led to a highly textured Nd2Fe14B phase, could be induced by slow desorption and recombination with a low driving force. Hydrogen desorption at a slower rate was important for achieving high magnetic anisotropy in the HDDR-processed Nd–Fe–B powders.

Effect of wheel speed on the crystallization behavior of as-quenched Nd-Fe-B alloys

A series of alloys composed of Nd9Fe85Nb0.5B5.5 were prepared through rapid quenching by different wheel speeds. Nanocomposite was usually obtained by subjecting the as-quenched alloys to a crystallization annealing. The crystallization behavior was investigated by differential scanning calorimetry (DSC) as the primary method. The results showed that the DSC curve of sample prepared at 15 m/s had only one exothermic peak at about 690 °C. When the wheel speed increased to 18-27 m/s, one more peak at 590 °C appeared. Moreover, the intensity of this new peak enhances while the original one at 690 °C declined as the speed increases within this range. When the speed further grew up to 30, 35, or 40 m/s , only the peak at 590 °C remained while the other disappeared. This could be ascribed to the different initial phase structures of the alloys, which were found to vary with the wheel speeds. As can be seen, with increasing the wheel speed, the contents of amorphous and metastable phase increased while Nd2Fe14B phase decreased. This change resulted in a huge effect on the crystallization behavior. We could deduce the relative content of each phase from the integral areas of peaks in DSC curves in different samples and figure out the phase transition in the crystallization. The results showed that the crystallization of samples prepared by relatively high speeds, which are almost amorphous initially, manifest as only one step, while those prepared by relatively low speeds showed two. Subsequently, we analyzed the crystallization process and interpreted it from the theory of energy barrier.