An Efficient Process for Recycling Nd–Fe–B Sludge as High-Performance Sintered Magnets

Given the increasing concern regarding the global decline in rare earth reserves and the environmental burden from current wet-process recycling techniques, it is urgent to develop an efficient recycling technique for leftover sludge from the manufacturing process of neodymium–iron–boron (Nd–Fe–B) sintered magnets. In the present study, centerless grinding sludge from the Nd–Fe–B sintered magnet machining process was selected as the starting material. The sludge was subjected to a reduction–diffusion (RD) process in order to synthesize recycled neodymium magnet (Nd₂Fe₁₄B) powder; during this process, most of the valuable elements, including neodymium (Nd), praseodymium (Pr), gadolinium (Gd), dysprosium (Dy), holmium (Ho), and cobalt (Co), were recovered simultaneously. Calcium chloride (CaCl₂) powder with a lower melting point was introduced into the RD process to reduce recycling cost and improve recycling efficiency. The mechanism of the reactions was investigated systematically by adjusting the reaction temperature and calcium/sludge weight ratio. It was found that single-phase Nd₂Fe₁₄B particles with good crystallinity were obtained when the calcium weight ratio (calcium/sludge) and reaction temperature were 40 wt% and 1050 °C, respectively. The recovered Nd₂Fe₁₄B particles were blended with 37.7 wt% Nd₄Fe₁₄B powder to fabricate Nd–Fe–B sintered magnets with a remanence of 12.1 kG (1 G = 1 × 10⁻⁴ T), and a coercivity of 14.6 kOe (1 Oe = 79.6 A·m⁻¹), resulting in an energy product of 34.5 MGOe. This recycling route promises a great advantage in recycling efficiency as well as in cost.     

The Effect of Tb80Fe20/Al Co-adding on Coercivity and Thermal Stability in Sintered Nd–Fe–B Magnets

Journal of Superconductivity and Novel Magnetism - The influence of Tb80Fe20/Al co-adding on coercivity and temperature stability of sintered Nd–Fe–B magnets was studied. Compared with...     

Magnetic Properties of Anisotropic Pr–Fe–B/Fe/Pr–Fe–B Films

Pr?CFe?CB/Fe/Pr?CFe?CB films with different Fe layer thicknesses were deposited by magnetron sputtering on Si (100) substrate heated at 650?°C. Structural and magnetic properties of the Pr?CFe?CB/Fe/Pr?CFe?CB films were investigated. X-ray diffraction and magnetic measurement results reveal that the Pr?CFe?CB/Fe/Pr?CFe?CB films are anisotropic when the thickness of Fe layer is smaller than 50?nm. The enhancement of the saturation magnetization in nanocomposite films is attributed to the exchange coupling between the soft and hard phases. The highest coercivity of about 13.9 kOe is achieved in the Mo(50?nm)/Pr?CFe?CB(50?nm)/Mo(2?nm)/Fe(2?nm)/Mo(2?nm)/Pr?CFe?CB(50?nm)/Mo(50?nm) film and increasing the thickness of soft-magnetic layer results in a continuous decreasing of the coercivity.     

Effects of Sintering Temperature on Microstructure and Magnetic Properties of Nd–Fe–B Magnets

The sintered Nd–Fe–B (neodymium–iron–boron) magnet has been used for many applications in various fields such as acoustics, communications, and automation due to its excellent properties including high remanence, high coercivity, and large energy product. Especially high-coercivity sintered Nd–Fe–B magnets have been extensively applied in the field of permanent magnet motors. In the present work, the effects of sintering temperature on the structural and magnetic properties of a Nd₁₅Fe₇₇B₈-type magnet have been investigated. Sintered permanent magnets were produced from a Nd₁₅Fe₇₇B₈ commercial alloy. The magnetic properties were evaluated using an Automatic Magnet Tester. The magnets were successfully produced at different temperatures. It was seen that the best magnetic properties were obtained for the magnet produced at 1050 ^°C for 1 h. The structural evolution of the magnets has also been examined by means of X-ray diffraction (XRD) and polarized optical microscope. Nd₂Fe₁₄B, Fe₃B and some α-iron phases were observed by X-ray diffraction results.     

Structural and Magnetic Properties of Nanocomposite Nd–Fe–B Prepared by Rapid Thermal Processing

Nanoscale permanent magnetic materials, which possess excellent magnetic and mechanical properties, thermal stability, and corrosion resistance, have become a research hotspot for permanent magnets. In reality, however, the obtained maximum energy product, (BH)_max, is not satisfactory in comparison with the theory limit, especially for exchange-coupled nanocomposite magnets. The construction of an ideal microstructure still remains a challenge in the synthesis and preparation of nanoscale permanent magnets. This work reported the impact of rapid thermal process (RTP) with electron-beam heating on the microstructures of Nd_12.5-xFe_80.8+xB_6.2Nb_0.2Ga_0.3 (x = 0, 2.5) nanocomposites. It was found that the crystallization time was greatly reduced, from 15 min under the conventional annealing conditions to 0.1 s under the RTP. For Nd₂Fe₁₄B single-phase materials, the crystallization temperature of the RTP ribbons decreased by about 248 °C compared with that of the ribbons produced by the conventional annealing method. A synergetic crystallization of the Nd₂Fe₁₄B and α-Fe phases was observed under the RTP, which restrained not only the shape, size distribution, and compositions of the hard and the soft phases, but also the interface between them. This modification effect became more obvious as the fraction of Fe increased. Due to the improvement in the uniformity of the Nd₂Fe₁₄B and α-Fe phases, and their grain size distribution, better magnetic properties were achieved using RTP in comparison with the conventional annealing method.     

Positron Annihilation Behaviors and Magnetic Properties of Single-phase Nd2Fe14B and Nanocomposite Nd2Fe14B／α- Fe Magnets

Positron annihilation behaviors have been studied in the single phase Nd2Fe14B magnet and the nanocomposite Nd2Fe14B/α-Fe magnet, prepared by melt spinning. The results showed that the number of vacancy-cluster at grain boundaries increases with increasing annealing temperature for the both types of magnets. The increase of this kind of defect can improve the coercivity of     

Evolution of microstructure in laser clad Fe–Cr–Mn–C alloy

Abstract

The laser surface cladding technique was used to form in situ Fe–Cr–Mn–C alloys on AISI 1016 steel substrate. In this process, mixed powders containing Cr, Mn, and C in the weight ratio 10: 1 : 1 were delivered using a screw feed, gravity flow, carrier gas aided system into the melt pool generated by a 10 kW CO₂ laser. This technique produced an ultrafine microstructure in the clad alloy layer. The microstructure of the laser surface clad region was investigated by optical, scanning and transmission electron microscopy, and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic transformation or retained austenite phase.

MST/356     

Nanocrystalline Nd–Fe–B Anisotropic Magnets by Flash Spark Plasma Sintering

Flash spark plasma sintering (flash SPS) is an attractive method to obtain Nd–Fe–B magnets with anisotropic magnetic properties when starting from melt-spun powders. Compared to the benchmark processing route via hot pressing with subsequent die upsetting, flash SPS promises electroplasticity as an additional deformation mechanism and reduced tool wear, while maximizing magnetic properties by tailoring the microstructure—fully dense and high texture. A detailed parameter study is conducted to understand the influence of Flash SPS parameters on the densification and magnetic properties of commercial MQU-F powder. It is revealed that the presintering conditions and preheating temperature before applying the power pulse play a major role for tailoring grain size and texture in the case of hot deformation via Flash SPS. Detailed microstructure and magnetic domain evaluation disclose the texture enhancement with increasing flash SPS temperature at the expense of coercivity. The best compromise between remanence and coercivity (1.37 T and 1195 kA m⁻¹, respectively) is achieved through a combination of presintering at 500 °C for 120 s and preheating temperature of 600 °C, resulting in a magnet with energy product (BH)_max of 350 kJm⁻³. These findings show the potential of flash SPS to obtain fully dense anisotropic nanocrystalline magnets with high magnetic performance.     

Evolution of microstructure and strength during the ultra-fast tempering of Fe–Mn–C martensitic steels

Ultra-fast tempering cycles, combining a rapid heating rate (R _H = 300 °C/s) from room temperature to a peak temperature within the range 400–700 °C and subsequent rapid cooling, were performed on a Fe–Mn–C martensitic steel. The influence of the peak temperature reached during the cycle was determined on both the tensile properties of the steel and on its microstructure. The mechanisms controlling the microstructural evolution occurring during rapid tempering were studied by combining both TEM observations and 3D reconstructions by FIB/SEM. A theoretical analysis coupled with the acquired experimental data was then proposed to explain the evolution of mechanical properties. The results obtained support the assumption that carbide precipitation during fast tempering plays a key role in the evolution of mechanical properties.     

Magnetic measurement of strain-induced martensite formation in Fe–30Ni steel

This investigation focuses on deformation-induced plasticity in Invar-type steel alloys. The effect is being studied in an austenitic model alloy, containing 30 wt-% of nickel. Its temperature dependent mechanical properties are being presented. Furthermore, the martensitic phase content has been determined by magnetic means in an alloy with two ferromagnetic phases for the first time. The results show that the α′-martensite formation within the austenitic phase with primarily wavy glide mechanism allows an increase in ductility of around 10% at the M_sσ temperature of ?5°C. This is the point of maximum uniform elongation. Near the M_s temperature, a microstructure of 70 vol.-% deformation-induced α′-martensite can be achieved.     

Pump–Probe Spectroscopy of Exciton Spin Injection Process in Diluted Magnetic Quantum Wells

Ultrafast spin dynamics of excitons is studied in a double quantum well composed of Cd_0.92Mn_0.08Te and CdTe wells with a Cd_0.80Mg_0.20Te tunnel barrier, in magnetic fields, by pump-and-probe absorption spectroscopy. The excitonic injection process is clarified with the injection time of 30 ps from the Cd_0.92Mn_0.08Te spin aligner to the CdTe spin detector. The time dependencies of circularly polarized differential absorbances show directly the spin injection into the CdTe well. The spin relaxation of the injected excitons is observed as a function of energy in the exciton band of the CdTe well. In addition, ultrafast relaxation processes of spin-polarized carriers in the Cd_0.78Mn_0.05Mg_0.17Te barrier are studied, when it is stacked directly with the CdTe well.     

XANES and XPS study of electronic structure of Ti-enriched Nd–Fe–B ribbons

Electronic structure of rapidly quenched ribbons of nominal composition Nd_yFe_(86−y−x)B₁₄Ti_x (x = 0, 2, 4; y = 7, 8 at.%) was studied by X-ray absorption (Fe and Ti K-edge) and X-ray photoelectron spectroscopy. It was found by XANES that Ti addition promotes modifications of the electronic structure of Fe sub-band. From the analysis of differences in the pre-edges structure areas, coming from variations in the 3d density of states near the Fermi level, the evidences of acceptor nature of Ti and Fe atoms in NdFeB alloys are present. Using photoelectron spectroscopy, we found that neodymium, iron and titanium are in both, metallic and oxidized, states on the surface of the ribbons. A higher Ti⁰ content (at high vacuum) is characteristic of the annealed samples. The presence of oxidized titanium states was corroborated by XANES.     

Experimental Analysis of Al–TiC Sintered Nanocomposite on EDM Process Parameters Using ANOVA

The size minimization of titanium carbide (TiC) particles was done by high-energy mechanical milling. Later Al and TiC powders were mixed to frame cylindrical preforms with 95% density using a die set. The cylindrical preform was sintered in a muffle furnace (575°C) and subsequently cooled. Characterization was done using scanning electron microscope (SEM), field emission scanning electron microscope, and energy-dispersive spectrum. An electrical discharge machining (EDM) and L9 orthogonal array was used to perform the experiments. The present investigation was carried out to optimize parameters such as current, pulse-on time, and gap voltage on metal removal rate (MRR) and tool wear rate (TWR) during EDM of as-sintered Al–5% reinforced with ≤200 nm and 2 µm TiC particle reinforcement. The rationality of the experimental plan and the effect of electrode wear ratio based on TiC particle addition were analyzed using analysis of variance (ANOVA) with consideration to MRR and TWR. The recast layer evolution during EDM process was assessed by SEM analysis.     

Nd－Fe－B滚镀锌工艺

Ｎｄ－Ｆｅ－Ｂ滚镀锌工艺晋西机器厂表面处理分厂（太原市０３００２７）李峰１前言钛铁硼烧结永磁体是继ＳｍＣＯ５和Ｓｍ２ＣＯ１７之后的第三代稀土永磁材料，由于钛铁硼永磁体具有高的磁化强度、矫顽力和磁能积，作为高技术领域中的磁性功能材料，具有广阔的应用前景...     

Nd－Fe－B永磁材料镀镍

针对Ｎｄ－Ｆｅ－Ｂ永磁材料组成元素钕（Ｎｄ）的氧化还原电势较负（－２．４４Ｖ）的特点，通过探索性试验，详细研试了Ｎｄ－Ｆｅ－Ｂ合金产品除油、出光和浸镀工艺的效果和工艺参数。结果表明，按照确定的工艺规范进行施镀，显著地提高了镀镍层与基体之间的结合强度，改善了镀镍层的质量。     

Improvement of corrosion resistance of Cu and Nb co-added Nd–Fe–B sintered magnets

Cu and Nb powders are co-added as intergranular modifiers to improve the corrosion resistance of Nd–Fe–B sintered magnets. For the magnet co-added with 0.2 wt.% Cu and 0.8 wt.% Nb, mass loss of accelerated corrosion test in 120 °C, 2 bar and 100% relative humid atmosphere for 96 h drops from 2.47 mg/cm² to 0.49 mg/cm² in comparison with the Cu/Nb free one. The corrosion potential E_corr in 3.5% NaCl aqueous solution increases from −1.115 V to −0.799 V, which indicates the better resistance against electrochemical corrosion. The improved corrosion resistance is ascribed to the enhanced stability of the intergranular phase by forming high electrode potential Cu-containing phase and reduced Nd-rich phase at triple junctions. Besides, the distribution of (Pr, Nd)-rich phases along the grain boundaries becomes more clear and continuous through Cu/Nb co-addition, maintaining fairly good magnetic properties of B_r = 13.6 kGs, H_cj = 11.4 kOe, (BH)_max = 46.2 MGOe. Further investigation demonstrates that Nb is effective to refine the grains of hard magnetic Nd₂Fe₁₄B phase and Cu is beneficial for optimizing the distribution of the intergranular phases.     

Positron annihilation study on deformation-induced Au precipitation in Fe–Au and Fe–Au–B–N alloys

We have investigated the potential self-healing of deformation-induced defects by Au precipitation during isothermal aging at 550 °C in Fe–Au and Fe–Au–B–N alloys using positron annihilation spectroscopy. Two different samples with 0 and 24 % pre-strain were used to study the influence of dislocations on the Au precipitation. Dislocations introduced prior to the aging process play an essential role in the formation of Au precipitates. The Coincidence Doppler broadening (CDB) technique shows that Au precipitation in the matrix occurs in the pre-strained samples only. TEM observations confirm the heterogeneous nature of the Au precipitation which occurs exclusively on dislocations and grain boundaries. The evolution of S and W parameters derived from the CDB indicates a three-stage precipitation process for the pre-strained samples. Both the hardness tests and the positron annihilation spectroscopy indicate that the addition of boron and nitrogen to the Fe–Au alloy causes a deceleration of the Au precipitation in the pre-strained samples, but does not alter the defect-induced mechanism of the Au precipitation. The defect-induced Au precipitation provides a promising site-specific autonomous repair mechanism to extend the lifetime of Fe-based alloys for high temperature structural applications.