A. Higgins

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.

Structure and magnetic properties of bulk isotropic and anisotropic Nd2Fe14B∕α-Fe nanocomposite permanent magnets with different α-Fe contents

Chemical coating, hot compaction, and hot deformation techniques have been applied to prepare bulk isotropic and anisotropic Nd2Fe14B∕α-Fe nanocomposite magnets. The effect of α-Fe content on the structure and magnetic properties of the magnets were studied. For the isotropic magnets, the remanence (Br) increases as the α-Fe content increases, while the coercive force (Hci) drops simultaneously. For the anisotropic magnets, the Br rises first, peaking at 2vol% of α-Fe content, then falls as the α-Fe content increases, and Hci drops significantly for all the α-Fe containing anisotropic magnets. Crystal structure analysis shows that only the magnets with no more than 2vol% α-Fe exhibit strong c-axis crystal texture of Nd2Fe14B phase after deformation. Microstructure observation also shows that there are many Nd2Fe14B equiaxial grains even after hot deformation in the magnets with α-Fe more than 2vol%.

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

An effort to increase the impact toughness of Nd–Fe–B sintered magnets by adding small amounts of Al, Nd, Ga, Cu, and Nb was successful. No significant compromise to magnetic properties occurred. Based on this work, a series of sintered Nd–Fe–B magnets with improved toughness was developed, which we call ToughNEO™. Small precipitates, which may contribute to the improvement of toughness, were observed using scanning electron microscope for all samples with improved toughness. Tumbling and drilling tests further verified the improved toughness of these developed ToughNEO™ magnets.

-Fe Composite Magnets by Applying Powder Coating Technologies

PrCo5 nanograin powders used for making bulk magnets were produced by surfactant-assisted high energy ball milling. Using a special compaction technique at 200–525 °C, PrCo5 bulk magnets were successfully prepared using the nanoflake powders. This kind of bulk magnet has a cluster microstructure and is nanocrystalline. The coercivity of the bulk magnet pressed at 200 °C is 5.22 kOe. It is found that the density of the bulk increases with the compaction temperature. Bulk magnet density up to 92% of the theoretical value has been obtained.

Microstructure and magnetic properties of sintered NdFeB magnets with improved impact toughness

Results from the neutron irradiation experiments show that the radiation tolerance is very high for Sm/sub 2/Co/sub 17/-type magnets and is fairly low for Nd-Fe-B-type magnets. The analyses show that the major radiation damage in permanent magnets is caused by a radiation-induced thermal spike accompanied by a localized temperature T/sub L/, and the radiation tolerance of a magnet is determined mainly by its thermal stability. The T/sub L/ value depends on the radiation intensity and the magnet composition. The thermal stability of a magnet at temperature below its Curie temperature is related to its intrinsic coercivity H/sub ci/ and its shape.

Preparation of PrCo5 bulk magnets using nanograin powders made by surfactant-assisted high energy milling

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.

The effect of neutron irradiation on Nd-Fe-B and Sm/sub 2/Co/sub 17/-based high-temperature magnets

Abstract Innovative and cost-effective technology for synthesizing bulk anisotropic nanograin composite rare earth magnets has been developed. Using a powder blending technique, ( BH ) max of nanograin composite magnets can reach 40 to 50 MGOe, while applying powder coating techniques, ( BH ) max = 45–55 MGOe were achieved. Thus, principal technical difficulties in synthesizing bulk anisotropic nanograin composite magnets are successfully overcome. In addition, it was observed that the magnetically soft phase in a composite magnet could be up to tens of micrometers, or more than 1000 times larger than the upper size limit predicted by the current models of interface exchange coupling, which indicates that further reducing the size of the soft phase and improving its distribution will significantly improve the magnetic performance of nanograin composite magnets.

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.

Research and Development of Bulk Anisotropic Nanograin Composite Rare Earth Permanent Magnets

In order to enhance magnetic properties of hybrid Pr₂(Fe,Co)₁₄B/PrCo₅ magnets, partial substitution of Fe for Co in the PrCo₅ component was made. This substitution resulted in significant deterioration of intrinsic coercivity of PrCo₅ and of the hot compacted hybrid Pr₂(Fe,Co)₁₄B/PrCo₅. However, after hot deformation, the intrinsic coercivity of hybrid Pr₂(Fe,Co) ₁₄B/Pr(Co_1-xFe_x)₅ increased with increasing Fe content in the Pr(Co_1-xFe_x)₅ component up to x=0.3. The SEM/EDS analysis revealed the formation of a Pr-rich Pr₂(Co_0.64Fe_0.36)₇ phase at the interface of Pr₂(Fe,Co)₁₄B and Pr(Co,Fe)₅. However, the mechanism of the coercivity enhancement is yet to be elucidated