M. Q. Huang

Bulk anisotropic composite rare earth magnets

Bulk anisotropic composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets with (BH)max=45–50MGOe have been synthesized by blending a Nd–Fe–Ga–B powder with an α-Fe or Fe–Co powder followed by hot compaction at 600–700 °C and hot deformation (die upsetting) at 850–950 °C with a height reduction of 71%. The composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets show microstructures consisting of a very large soft phase up to ∼50μm, which is more than 1000 times larger than the upper size limit of the soft phase expected from the existing models of interface exchange coupling.

Bulk isotropic and anisotropic nanocomposite rare-Earth magnets

Bulk, isotropic and anisotropic nanocomposite magnets of (Nd,Pr,Dy)/sub x/Fe/sub 100-x-y-z-u-v/Co/sub y/Al/sub z/Ga/sub u/B/sub v/ with x= 8-11.6, y= 6-6.3, z= 0-0.2, u= 0-0.2, and v= 5.6-10.0 were prepared and their magnetic properties as functions of rare-earth content, hot press temperature, and hot-deformation amount were investigated. For isotropic nanocomposite magnets, the best (BH)/sub max/ of 16.2 MGOe was obtained when hot pressing Nd/sub 9.3/Pr/sub 0.5/Dy/sub 0.2/Fe/sub 77.7/Co/sub 6.3/Al/sub 0.2/Ga/sub 0. /2B/sub 5.6/ at 660/spl deg/C. The magnetic performance of anisotropic nanocomposite magnets is strongly dependent on the rare-earth content and the hot deformation amount. The best (BH)/sub max/ of 42 MGOe was achieved in a hot-deformed Nd/sub 10.8/Pr/sub 0.6/Dy/sub 0.2/Fe/sub 76.1/Co/sub 6.3/Al/sub 0.2/Ga/sub 0 /./sub 2/B/sub 5.6/ magnet with 70% height reduction.

Enhancing Magnetic Properties of Bulk Anisotropic Nd–Fe–B/

Bulk anisotropic composite Nd14Fe79.5Ga0.5B6/alpha-Fe magnets with (BH)max=45-55 MGOe were synthesized by compacting Nd-Fe-Ga-B powders coated with thin alpha-Fe layers followed by hot compaction at 600degC to 700degC and hot deformation (die upsetting) at 850degC to 950degC with a height reduction of 71%. The coating techniques used include DC and RF sputtering, pulsed laser deposition, chemical coating, and electrolytic coating. Composite magnets prepared using these techniques demonstrate enhanced intrinsic coercivity and significantly improved squareness of intrinsic demagnetization curves

alpha

SmCo5(1−x)Fex (x=0.2, 0.4, 0.6, and 0.7) nanocomposites were synthesized by ball milling a mixture of SmCo5 and nanosize iron powders. Composites were made using different kinds of soft ferromagnetic phase nanoparticles, either α-Fe crystallized from amorphous iron generated by sonochemical decomposition of Fe(CO)5, or acicular metallic iron particles with an average length of 200 nm and average diameter of 18 nm. After milling the powder mixtures were compacted by hot isostatic pressing at 3000 psi for ∼5 min at a temperature of 530–570 °C. The compacted solids were magnetically characterized between 5 and 300 K. Hysteresis loop measurements and recoil measurements for the (SmCo5)0.8/acicular-Fe0.2 composite show stronger magnetic coupling when compared with the properties of (SmCo5)0.8/amorphous-Fe0.2, am-Fe coated SmCo5, and pure SmCo5 powders alone.

-Fe Composite Magnets by Applying Powder Coating Technologies

We have investigated the microstructures of melt-spun Sm(Co0.58Fe0.31Cu0.04Zr0.05B0.02)z (z=7.5 and 12) ribbons by transmission electron microscopy (TEM) and three dimensional atom probe (3DAP) to correlate them with the hard magnetic properties. The ribbon with z=7.5 has a high coercivity (iHc∼12 kOe) while the ribbon with z=12 possesses a low coercivity (iHc∼4.9 kOe). The high iHc ribbon comprises of nanocrystals (∼10 nm) having 1:7H (TbCu7) type structure as main phase. However, in the low iHc ribbon, the microstructure consists of both 1:7H and 2:17H (Th2Ni17) phases with crystal size ranging from 50 to 80 nm. The low coercivity ribbon also contains (CoFeZr)23B6 (M23B6 type) soft magnetic phase. The low coercivity obtained in the melt-spun ribbon with z=12 is due to: (i) the formation of Th2Ni17 type low anisotropy phase, (ii) the presence of boron-rich soft magnetic phase, and (iii) larger crystal size. Realization of high coercivity in the ribbon with z=7.5 is due to the formation of 1:7H, a high an...

Synthesis and magnetic behavior of SmCo5(1−x)Fex nanocomposite magnets

Attempts to fill a wide gap in thermal stability between Nd–Fe–B and Sm–Co based magnets by making a conventional hybrid Nd15Fe79B6∕Sm(Co,Fe,Cu,Zr)7.4 type of magnets encountered two technical difficulties: incompatible processes and interdiffusion between two materials. Because a fundamental change in coercivity mechanism occurs when reducing the grain size in these magnets to nanometer range, high coercivity can be obtained in both nanograin Sm2(Co,Fe)17 and Nd2Fe14B after a short anneal at ∼700°C. Thus, the processes of making two different nanograin magnets are completely compatible. Further, very short time of elevated temperature processing can minimize the interdiffusion. Applying this approach, hybrid nanograin Nd2Fe14B∕Sm2(Co,Fe)17 magnets with (BH)max=27.4MGOe and HcM=14kOe were made using rapid inductive hot compaction and hot deformation. In addition, better magnetic performance of (BH)max=34.5MGOe and HcM=16.9kOe was obtained in a hybrid nanograin Pr2(Fe,Co)14B∕Pr(Co,Fe)5 (80wt%∕20wt%) magnet.

Microstructure and magnetic properties of melt-spun Sm(Co0.58Fe0.31Cu0.04Zr0.05B0.02)z ribbons

Fe–Co alloys are extensively used in lamination form, but there are certain power generation applications that require Fe–Co rotors in bulk form. Experiencing only a dc magnetic field, these rotors can be as large as 0.5m in diameter, depending on the size of the generator. The forging of such large pieces of Fe–Co has proven to be difficult. The present study investigates powder metallurgy processing of a gas atomized FeCoNbV alloy through hot isostatic pressing (HIP) for manufacturing large size rotors with improved mechanical strength. Gas atomized FeCoNbV alloy powders with and without ball milling were hot isostatic pressed at temperatures between 675 and 850°C at a fixed pressure of 193MPa for up to 6h. Ball milling prior to HIP improved the yield strength. A further improvement in yield strength and in ductility was obtained after a disordering heat treatment at 730°C followed by a rapid quench to room temperature. The optimum HIP and annealing conditions resulted in samples with yield strengths of...

Hybrid nanograin rare earth magnets with improved thermal stability

Structure and magnetic properties of both melt-spun and hot deformed bulk Sm–Co type nanocomposite magnets have been investigated with various metal additions, including Zr, Cu, and Nb. The Zr and Nb additions play important roles in constraining grain growth, resulting in an increase of coercivity Hc. The Cu addition significantly improves the squareness of BH loops as well as the energy product (BH)max. A typical hot deformed bulk anisotropic nanocomposite SmCo type magnet with Mr(hard)∕Mr(easy)∼0.4, Hc∼9kOe and (BH)max of 13.2MGOe was obtained.

High strength bulk Fe–Co alloys produced by powder metallurgy

Fully dense anisotropic nanocomposite Sm(Co0.58Fe0.31Zr0.05Cu0.04B0.02)z (z=7.5–12) magnets have been synthesized via rapid hot pressing and hot deformation processes. The highest (BH)max∼10.6MGOe was observed for a magnet with z=10. X-ray diffraction and M-H measurements indicated that the easy magnetization direction of magnets prefers to be in the hot pressing direction. Transmission electron microscopy investigation confirmed that plastic deformation is an important route for forming magnetic anisotropy in the Sm–Co-type nanocomposite magnets. Some stripe and/or platelike patterns have been observed inside the nanograins (50–200nm), which may present as twins, and stacking faults. The (0001) twins have been observed in the 2:17R phase.Fully dense anisotropic nanocomposite Sm(Co0.58Fe0.31Zr0.05Cu0.04B0.02)z (z=7.5–12) magnets have been synthesized via rapid hot pressing and hot deformation processes. The highest (BH)max∼10.6MGOe was observed for a magnet with z=10. X-ray diffraction and M-H measurements indicated that the easy magnetization direction of magnets prefers to be in the hot pressing direction. Transmission electron microscopy investigation confirmed that plastic deformation is an important route for forming magnetic anisotropy in the Sm–Co-type nanocomposite magnets. Some stripe and/or platelike patterns have been observed inside the nanograins (50–200nm), which may present as twins, and stacking faults. The (0001) twins have been observed in the 2:17R phase.

Effects of Zr, Nb, and Cu substitutions on magnetic properties of melt-spun and hot deformed bulk anisotropic nanocomposite SmCo type magnets

Bulk Sm-Co/α-(Fe,Co) nanocomposite magnets were fabricated by hot pressing composite powders prepared by high-energy ball milling of magnetically hard SmCo5 powder and magnetically soft Fe powder. The bulk magnets had a nanocomposite structure consisting of Sm-Co matrix (1:5 H and 1:7 H phases) and α-(Fe,Co) phases. The Fe-Co particles were distributed uniformly in the Sm-Co matrix. The milling time strongly affects the structures and the magnetic properties of the bulk magnets. Increasing milling time led to a decrease of the amount of 1:5 H phase, an increase in the phase fraction of the 1:7 H phase, and a decrease in the amount of soft phase, which resulted in an increase in magnetization and a decrease in coercivity. Scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) analyses revealed that inter-diffusion took place between the Sm-Co matrix and Fe particles during the processing.