Shigeho Tanigawa

Nd‐Fe‐B die‐upset and anisotropic bonded magnets (invited)

The hot working conditions were examined for Nd‐Fe‐B die‐upset magnets. The Nd14Fe80B6 ternary composition has the best workability (die upsetting) from stress‐strain curves for the initial stage of die upsetting at hot working temperature. The compression ratio defined as the inverse of reduction in height should be larger than 4 to have materials aligned. Alignment of c axis along the compressive stress direction is obtained, but grain coarsening occurs during die upsetting. Of several additional elements investigated, Ga is the best for enhancing the coercivity with a little sacrifice of remanence and no deterioration in hot workability. Typical magnetic properties for Nd14Fe79.25B6Ga0.75 die‐upset magnets are Br =12.4 kG, iHc =19 kOe, and (BH)max =36 MGOe. The irreversible loss after exposure up to 160 °C is under 10% (Pc =2). The iHc of powder made by crushing the die‐upset magnets is nearly independent of particle size. Decrease in iHc by pulverizing to several hundred micron is about 2 kOe. Anisotropic bonded magnets were developed using this powder. Best energy products of injection and compression molded magnets with Ga addition are 10 and 15 MGOe, respectively. The irreversible losses after exposure up to 120 °C is lower than 5% (Pc =2), which is enough thermal stability for polymer‐bonded magnets.The hot working conditions were examined for Nd‐Fe‐B die‐upset magnets. The Nd14Fe80B6 ternary composition has the best workability (die upsetting) from stress‐strain curves for the initial stage of die upsetting at hot working temperature. The compression ratio defined as the inverse of reduction in height should be larger than 4 to have materials aligned. Alignment of c axis along the compressive stress direction is obtained, but grain coarsening occurs during die upsetting. Of several additional elements investigated, Ga is the best for enhancing the coercivity with a little sacrifice of remanence and no deterioration in hot workability. Typical magnetic properties for Nd14Fe79.25B6Ga0.75 die‐upset magnets are Br =12.4 kG, iHc =19 kOe, and (BH)max =36 MGOe. The irreversible loss after exposure up to 160 °C is under 10% (Pc =2). The iHc of powder made by crushing the die‐upset magnets is nearly independent of particle size. Decrease in iHc by pulverizing to several hundred micron is about 2 kOe. Anisotr...

Some heat treatment experiments for Nd-Fe-B alloys

Since the Curie temperature (Tc) of R-Fe-B permanent magnets is lower than conventional 1/5 and 2/17 magnets, the irreversible loss due to the change of coercivity is critical when considering their application. The simple way to guarantee the thermal properties is to raise the coercivity at room temperature. The effect of heat treatment on coercivity was studied. The typical heat treatment is as follows: (1) The first heating at T 1 , 900°C × 2 hrs is followed by the continuous cooling at the rate of 1.3°C/min to room temperature. (2) The second heating at T 2 , near the eutectic temperature for 1 hr is followed by quenching. When employing this heat treatment, the following magnetic properties were obtained for Nd(Fe 0.92 B 0.08 )6. Br=13800 G, bH c =9150 Oe, iHc=9200 Oe and (BH)max=44.0 MGOe.

Micromagnetic studies of inhomogeneous nucleation in hard magnets

Abstract Nucleation fields of reversed domains in hard magnets with magnetic planar defect are calculated based upon micromagnetism. We show that the reversal processes are classified into three types depending on the parameters characterizing the defect. In a certain region of the parameters, there exists the case where the magnetization in the defect is forced to rotate reversely by an applied field which does not yet bring about the reversal rotation in the host matrices. We suggest that this situation gives a crucial role for the angular dependence of the nucleation fields in Ne-Fe-B sintered magnets.

Development of an Axial Gap Motor With Amorphous Metal Cores

This paper presents a novel motor design concept that utilizes amorphous cut cores in the stator and ferrite magnets in the rotor to obtain a high-efficiency motor. This motor employs a six-pole nine-slot axial gap construction and aims to provide 90% efficiency with decreased size and low cogging torque for fan motor applications. Amorphous cut cores are applied to the stator to decrease iron loss and save motor space. Skewed magnets are employed to decrease cogging torque. Three-dimensional finite element analysis was used to analyze motor performance. In order to verify the accuracy of the design, a trial motor was constructed, and a large range of experiments was conducted to measure the motor characteristics. The results of the trial motor meet the design goals.

Ga added Nd-Fe-B sintered and die-upset magnets

The addition of Ga to Nd-Fe-B sintered and die-upset magnets in order to improve thermal stability was examined. The Ga addition increases the coercivity of Nd(Fe/sub 0.72/Co/sub 0.2/B/sub 0.08/)/sub 5.6/ sintered magnets markedly. Ga addition does not enhance coercivity of sintered magnets with lower Co substitution. Ga addition increases coercivity for Nd-Fe-B die-upset magnets. No decrease in coercivity due to Co substitution of up to 20 at.% is observed for Nd/sub 14/Fe/sub 79.25/B/sub 6/Ga/sub 0.75/ die-upset magnets. This is an advantage of the die-upset magnets compared with the sintered magnets. Ga has a tendency to occur in the Nd-rich phase at higher concentrations than 2 wt.%, and Ga content in the 2/14/1 matrix is around 0.2 wt.% for Nd/sub 14/Fe/sub 79.25/BGa/sub 0.75/ die-upset magnets. For sintered magnets, Ga is distributed between the matrix and the Nd-rich phase. H/sub A/ of the 2/14/1 matrix is increased by Ga addition up to 2.5 at.%. The correlation between H/sub A/ and iH/sub c/ is not good. The Ga-containing Nd-rich phase is observed in the sintered magnets, and the role of Ga in this phase needs to be evaluated to understand coercivity enhancement by Ga addition. >

Magnetic properties of isotropic and anisotropic Nd-Fe-B bonded magnets

Abstract A trial to make Nd-Fe-B rapidly quenched flakes anisotropic by grain growth during heat treatment in the magnetic field has been carried out. No magnetic anisotropy is observed, but the optimum heat treatment temperature is lowered by about 100°C by applying 14 kOe of magnetic field. There is, as yet, no explanation of this phenomenon. Another way of making anisotropic bonded magnets is to use pulverized powders of anisotropic dense die-upset magnets as a starting material. By examination of the process parameters for Nd-Fe-B die-upset magnets it was found from stress-strain curves that the Nd 14 Fe 80 B 6 ternary composition has the best workability and to achieve aligned material the compression ratio (defined as the inverse of reduction in height) should be larger than 4. Grain coarsening resulted in a decrease in coercivity ( i H c ) during die upsetting. Ga is the best additional element for enhancing i H c with a little sacrifice of remanence ( B r ) and no deterioration in hot workability. Further improvement of thermal stability by raising the Curie temperature ( T c ) of the Nd-Fe-B-Ga alloy can be achieved by Co substitution. The i H c of the powder made by pulverizing the die-upset magnets is nearly independent of particle size. Anisotropic bonded magnets were developed using this powder. The ( BH ) max of compression-moulded magnet with Ga addition and Co substitution, Nd 14 Fe 71.75 Co 7.5 B 6 Ga 0.075 , is 15 MGOe. The irreversible losses after exposure up to 140°C is lower than 5% ( P c =2), which is sufficient thermal stability for polymer-bonded magnets.

Development of a high speed motor using amorphous metal cores

This paper presents the development of a 10kr/min motor that utilizes the amorphous toroidal core. This motor employs a non-slotted axial gap structure with two ferrite magnet rotors and one amorphous toroidal stator. The goal of the motor is to produce a 400W output, at 90% high efficiency with a size of Φ100×L30. The low core loss design is employed to decrease the large core losses produced by a high frequency field. The motor design equations and three dimensional finite element analysis (3D FEA calculations) are presented. A prototype machine was manufactured. The structure of the prototype and the test results are presented in this paper.

Development of an axial gap motor with amorphous metal cores

This paper presents a noble motor design concept that utilizes amorphous cut cores in the stator to obtain a high efficiency motor. This motor employs 6-pole, 9-slot axial gap construction and aims to provide high efficiency with small size and low cogging torque for fan motor applications. Amorphous cut cores are applied to the stator to decrease iron loss and save motor space. The magnets with distinct shapes are employed to decrease cogging torque. 3D finite element analysis was used to model and analyze motor performance. In order to verify the design concept, a trial motor was constructed and a large range experiments were conducted to measure motor characteristics.

Effect of coarse grains on magnetic properties of Nd-Fe-Co-B-Ga die-upset magnets

Coarse grains contained in Nd-FeCo-Ga-B hot-pressed and die-upset magnets are examined. Coarse grains contained in hot-pressed magnets are found to maintain their shapes during die upsetting and to increase deformation resistance B/sub r/, H/sub k/, and (BH)/sub max/ of die-upset magnets decrease with increase in the volume fraction of coarse grains. Equiaxed coarse grains nucleate and grow during melt spinning. Columnar coarse grains grow during hot pressing. It is shown that the volume fraction of coarse grains before die upsetting should be minimized to increase (BH)/sub max/. >

Rare earth magnets for applications over a wide temperature range

Abstract Sm2Co17-type sintered magnets and Nd-Fe-B die-upset magnets have been investigated over the temperature range 4.2–423 K. Their magnetic properties were compared with those of SmCo5 and Nd-Fe-B sintered magnets. This study indicates that the Sm2Co17-type magnets appear to be the best for applications at high temperatures up to 423 K. The magnetic properties of a Sm2Co17 magnet at 423 K are: Br = 10.8 kG, iHc = 15.7 kOe and (BH)max = 27.1 MGOe. The irreversible loss of the Sm2Co17 magnet at a permeance coefficient of 2 is 1.1% after exposure at 573 K for half an hour. Sintered Nd-Fe-B magnets exhibit better thermal stability compared to their die-upset conterparts. The second quadrant loop of the Nd-Fe-B magnets exhibit an anomalies behavior at 4.2 K due to the spin reorientation phenomenon which occurs at 140 K.