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.     

Fabrication of Iron-base Alloy by Spark Plasma Sintering

Fe-2Cu-2Ni-lMo-0.8C (wt pct) elemental mixed powders were rapidly sintered within 6 min by spark plasma sintering, and the effects of sintering parameters on the densification degree and performance of the assintered materials were investigated. Results showed that when a proper combination of pulse electric current and constant electric current was employed for sintering, the density and bend strength of the as-sintered material reached the maxima, being 7.61×103 kg/m3 and 1540 MPa, respectively. Its corresponding fracture morphology was characterized as the mix of ductile, intergranular and cleavage fractures.     

Microwave Plasma Sintering of Nanocrystalline Alumina

Sintering of nanocrystalline alumina by microwave plasma has been studied. The relative density,microhardness of the samples with different grain sizes by microwave plasma and other sintering techniques have been compared     

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.     

In situ boron carbide–titanium diboride composites prepared by mechanical milling and subsequent Spark Plasma Sintering

Boron carbide–titanium diboride composites were synthesized and consolidated by Spark Plasma Sintering (SPS) of mechanically milled elemental powder mixtures. The phase and microstructure evolution of the composites during sintering in the 1,200–1,700 °C temperature range was studied. With increasing sintering temperature, the phase formation of the samples was completed well before full density was achieved. The distribution of titanium diboride in the sintered samples was significantly improved with increasing milling time of the Ti–B–C powder mixtures. A bulk composite material of nearly full density, fine uniform microstructure, and increased fracture toughness was obtained by SPS at 1,700 °C. The grain size of boron carbide and titanium diboride in this material was 5–7 and 1–2 μm, respectively.     

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.     

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...     

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     

Nanocrystalline FeNi solid solutions prepared by mechanical alloying

Mechanical alloying of FeNi36 was performed by the ball milling process. XRD studies revealed that the alloy was crystallized in a stable FCC phase. Structural analysis of the samples pointed out a crystallite size to 10 nm. Thermogravimetric measurements allowed the detection of both CO and CO₂. During thermomagnetic analyses, we observed unusual response of our samples.     

Nanocrystalline CuFe solid solutions prepared by mechanical alloying

Nanocrystalline Cu_xFe(100_−x) solid solutions have been prepared by mechanical alloying. The average grain size of the powders (10–20 nm) depends on the composition of the material. The detailed process of nanocrystal formation was characterized by high resolution electron microscopy and many fine structure changes were revealed. The enhancement of solid solubility is explained according to the structural features of nanocrystals.     

Magnetic Domain Evolution in Sintered Nd–Fe–B Magnet during Magnetization Process

In the present study, the magnetic domains and their evolution during magnetization process have been investigated for sintered Nd–Fe–B permanent magnets with Kerr microscopy. Observation of the magnetic domain evolution process during magnetization process shows that some domain walls were pinned at the grain boundary area under magnetic field up to 5 kOe. It is suggested that magnetic interaction between individual Nd₂Fe₁₄B grains contacting to each other leads to appearance of small closed domains near the grain boundary area, which are responsible for the pinning effect.     

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.     

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.     

Nanocrystalline microstructures in Fe93 − x Zr7B x alloys

The crystallization behaviour of amorphous Fe_{93 – x} Zr₇B _x (x = 3, 6, 12 at.%) alloys, the microstructures of the primary crystallization products of stable and metastable phases and the subsequent transformations, have been studied using a combination of differential scanning calorimetry, differential thermal analysis, X-ray diffraction and transmission electron microscopy, including microdiffraction. It has been found that, for x = 3 and 6 at.%, the sole product of primary crystallization is the bcc -Fe phase and the average grain sizes of the crystalline phase were 14 nm and 12 nm for the two alloys, respectively. However, when x = 12 at.%, primary crystallization results in more than one crystalline phase, and a metastable phase with the cubic Fe₁₂Si₂ZrB structure is the major crystallization product after the primary crystallization reaction, accompanied by the -Fe phase. The average grain size of this metastable phase was 35 nm for the alloy heated to 883 K at 20 K/min. Isothermal heat treatments at 873 K and 973 K confirm that after being heated for 240 h, this metastable phase transforms into equilibrium phases: bcc -Fe, hcp ZrB₂ and probably hcp Fe₂Zr. The apparent activation energies for the primary crystallization reaction during continuous heating for these three alloys are 4.4 ± 0.2 eV, 3.5 ± 0.2 eV and 6.9 ± 0.3 eV, respectively.     

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。