NdFeB-type Permanent Magnets Research Articles

Morphology of NdFeB-Type Permanent Magnet Coercivity Enhancement by Heat Treatment Process

To understand the morphology of the coercivity enhancement by heat treatment, a commercial sintered NdFeB-type permanent magnet is annealed, and the coercivity is measured by Permagraph. It is shown that the coercivity is increased compared to the initial. Observation by X-Ray Diffraction (XRD) analysis and Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDS) is then conducted. The XRD result shows the amount of NdFeB content in the NdFeB-type permanent magnet is increased after heat treatment. The more significant amount of NdFeB content causes higher coercivity. The maximum coercivity, 19 kOe, is achieved at 850 °C of heat treatment temperature, where the NdFeB content is at the highest amount. Microstructural characterizations using SEM-EDS show that at 850 °C of heat treatment temperature, the iron (Fe) content in the grain boundaries is the lowest. It causes higher coercivity. This is due to the magnetically decoupled between NdFeB grains. The decoupling magnet of the NdFeB grains is affected by the Fe content in the grain boundaries. High-temperature heat treatment at 900 and 1050 °C led to the decomposition of NdFeB content in the grains and increased the Fe content in the grain boundaries, which resulted in a substantial reduction of magnetic coercivity.

Operation Characteristic of IPMSM Considering PM Saturation Temperature

In this study, the operation characteristics of an interior permanent magnet synchronous motor (IPMSM) for an electric oil pump (EOP) are analyzed, based on the irreversible demagnetization of the permanent magnet due to temperature saturation. EOP motors are targeted to operate at low-speed high-torque and high-speed low-torque under low and high temperatures, respectively. Hence, the operating temperature is essential for determining the performance characteristics of these motors. Moreover, as a NdFeB type permanent magnet (PM) is utilized, the motor is vulnerable to high temperatures in terms of the irreversible demagnetization of the PM. In this study, the output performance and PM demagnetization ratio of an IPMSM is analyzed at a target ambient temperature. Subsequently, the saturation temperature for each operating point is derived using MotorCAD, which is based on a precise analysis of the thermal equivalent circuit. Finally, the IPMSM for an EOP is analyzed using the derived saturation temperature and compared to the that derived using the ambient temperature.

Cogging Torque Reduction of Sandwiched Stator Axial Flux Permanent Magnet Brushless DC Motor using Magnet Notching Technique

Cogging torque reduction of axial flux permanent magnet brushless dc (PMBLDC) motor is an important issue which demands attention of machine designers during design process. This paper presents magnet notching technique to reduce cogging torque of axial flux PMBLDC motor designed for electric vehicle application. Reference axial flux PMBLDC motor of 250 W, 150 rpm is designed with 48 stator slots and 16 rotor poles of NdFeb type permanent magnet without notching. Three dimensional finite element modeling and analysis is performed to obtain cogging torque profile of initially designed reference machine. Notches are created on permanent magnets and its influence on cogging torque is analyzed with 3-D finite element modeling and analysis. It is analyzed that magnet notching is an effective technique to reduce cogging torque of axial flux PMBLDC motor.

The Hydrogen Ductilisation Process (HyDP) for shaping NdFeB magnets

One of the major drawbacks of NdFeB–based, fully dense, sintered magnets is that they are hard and extremely brittle. Therefore, in order to produce the final shape and precise dimensions, they often have to be ground and this process is time consuming, energy intensive and produces a significant amount of waste material which is not readily recyclable. This paper reports a potentially new and exciting application of hydrogen as a promising processing tool in which the normally brittle Nd2Fe14B based intermetallic could be compressed at room temperature in a ductile, disproportionated condition and then restored to its original state by the removal of the hydrogen under partial vacuum at elevated temperatures. Under appropriate conditions, this stage can also produce a useful degree of anisotropy. This paper describes the salient feature of this process which has been called the Hydrogen Ductilisation Process (HyDP) and describes possible applications of the HyDP in the production of NdFeB-type permanent magnets.

Developments in the Processing and Properties of NdFeB‐Type Permanent Magnets

AbstractFor Abstract see ChemInform Abstract in Full Text.

Developments in the processing and properties of NdFeb-type permanent magnets

The composition, microstructure and processing of NdFeB-type permanent magnets are all critical factors for the successful production of high performance magnet components. Three common fabrication routes can be used to categorize these NdFeB-based bulk magnets: sintering, polymer bonding and hot deformation. Generally, the former type of magnet has a high-energy product (30–50 MGOe), full density and a relatively simple shape. Bonded magnets have intermediate energy products (10–18 MGOe), lower density and can be formed into intricate net-shapes. Hot deformed magnets possess full density, intermediate to high-energy products (15–46 MGOe), isotropic or anisotropic properties and have the potential to be formed into net shapes. This article discusses the critical issues of improved magnetic performance, environmental stability, net-shape formability and magnetization behavior for the main categories of NdFeB magnets.

Magnetic viscosity and barkhausen noise in NdFeB-type permanent magnets

The Barkhausen noise and magnetic viscosity in sintered and melt-quenched needles of anisotropic NdFeB-type magnets are examined. In the sintered magnet, the time integral of the Barkhausen signal during magnetic viscosity is shown to correlate with the change in the bulk magnetisation as measured using a vibrating sample magnetometer. This is in contrast with similar measurements on soft magnetic materials by Tebble et al. [1], where the magnetisation change, as estimated from the time integral of the Barkhausen noise, was significantly less than that measured by magnetometric techniques. The activation volume in each of the two materials is estimated from measurements of the coefficient of magnetic viscosity, S v, and in the case of the sintered magnet is shown to be up to 13 orders of magnitude smaller that the largest Barkhausen volumes associated with the demagnetisation process. The magnitude of the Barkhausen volumes are indicative of magnetisation processes involving instabilities in the magnetisation of clusters of grains. It was not possible to identify heterogeneities in the microstructural or magnetic topology in these materials which would account for the magnitudes of the observed Barkhausen jumps.

Enhanced corrosion resistance of NdFeB type permanent magnet coated by a dual layer of either Ti/Al or Ni/Al intermetallics

NdFeB magnets were coated with a dual layer of either Ti/Al or Ni/Al by thermal evaporation. When the coated samples were annealed at 400/spl deg/C, intermetallic reactions occurred within these coatings, between Ti and Al, and between Ni and Al. When the samples were annealed at 500/spl deg/C, the reaction were extended to the matrix of the magnet forming Al/sub 36/Ti/sub 43/Fe/sub 17/Nd/sub 4/ in the sample coated with Ti/Al, but forming Ni/sub 2/AlFe/sub 0.1/ in the Ni/Al coated sample. The presence of these intermetallics were confirmed by leaching the coated magnets in NaOH. We had observed that the annealed Ti/Al coated sample had a smooth surface, while that of the Ni/Al was porous with microcracks as a result of the volume contraction of the Ni/Al layer. It was also found that Nd in the Nd-rich grain boundaries of the magnet tended to react actively with the dual layers. The areas involved would be extended as the annealing temperature and time increased. This shows that the quality of the resultant intermetallic coating depends upon the microstructure of the NdFeB magnet. Furthermore, the adhesion between the coating and the magnet can be improved greatly by the appropriate heat treatment.

Magnetic properties of novel resin-bonded exchange coupled rare-earth magnets

The magnetic properties of compaction-molded resin-bonded magnets which exhibit exchange spring behaviour have been measured. The starting compositions of the alloys were Nd 4.5Fe 73B 18.5Co 3Ga 1 and Nd 3.5Dy 1Fe 73B 18.5Co 3Ga 1 and the preparation method consisted of melt-quenching followed by annealing for a short period. The magnets have remanent magnetisation approximately 70% of saturation magnetisation. The variation of the magnetic properties with temperature in the range 250–320 K has been investigated and magnetic viscosity measurements have been made. These data are compared with those from a conventional resin-bonded NdFeB-type permanent magnet. It has been found that the exchange coupled materials have smaller variations in magnetic properties over the temperature range investigated, and they exhibit less time dependence of magnetisation, compared with the conventional material.

Mössbauer and X-ray study of NdFeB type permanent magnets oxidation: Effect of A1 and Nb addition

The influence of Al and Nb addition on the corrosion behaviour of NdFeB permanent magnets is studied by Mössbauer spectrometry and X-ray diffraction. At 200°C, results show that Al and Nb slow the oxidation kinetics of the Nd 2Fe 14B phase, indicating an increase of the corrosion resistance due to these dopants.

The magnetic and mechanical properties of NdFeB type permanent magnets and the effect of quenching

The fracture strength of Nd/sub 15/Fe/sub 77/B/sub 8/ and Nd/sub 14.5/Dy/sub 1.5/Nb/sub 1/Fe/sub 76/B/sub 7/ sintered magnets has been measured to be 285(40) MPa and 240(48) MPa, respectively. The fracture mechanism appears to be controlled by a critical level of tensile stress. In all the cases considered, Nd-Fe-B-type permanent magnets have been shown to fracture in a brittle manner along the grain boundaries. This is consistent with poor adhesion between Nd/sub 2/Fe/sub 14/B grains and could be due to the lack of the neodymium-rich phase along certain interfaces even in the fully sintered condition. The addition of dysprosium and niobium to the Nd-Fe-B alloy did not alter the fracture behavior of the material, whereas these additions have a marked effect on the magnetic properties. Quenching from 1370 K was found to greatly affect the fracture stress. This is possibly due to rapid cooling through the melting point of the neodymium-rich phase, which prevents sufficient wetting of the grains. Indeed, when the quench rate was increased the effect was so severe that some samples were prone to fail on pulse magnetization. However, where this did not occur, the effect was reversible on annealing at 903 K for 1 h. The intrinsic coercivity decreased progressively with increasing quench temperature above 900 K. This could be due to progressively less wetting with increasing quench temperature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>