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  • 1
    Electronic Resource
    Electronic Resource
    Explosive compaction of Magnequench Nd–Fe–B magnetic powders : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4851-4853 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnequench NdFeB powders having high and low rare earth contents were explosively compacted to obtain cylindrical magnets. The magnetic properties were found to be isotropic and were superior to conventionally consolidated isotropic magnets. The (BH)max was 14.7 MGOe and the remanence was 8.7 kG for the explosively compacted magnet with lower rare earth content. X-ray diffraction patterns confirm the explosively compacted magnet to be crystalline and the predominant phase to be the 2-14-1 phase. Transmission electron microscopy examination showed a microstructure to consist of 20–25 nm size equiaxed grains consistent with the magnetic measurements. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361631
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  • 2
    Electronic Resource
    Electronic Resource
    Study of desorbed hydrogen-decrepitated anisotropic Nd-Fe-B powder using x-ray diffraction : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6259-6261 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intrinsic magnetic coercivity (Hci) of Nd-Fe-B-based permanent magnet material is profoundly affected by hydrogen absorbed during the hydrogen decrepitation (HD) process for producing anisotropic powders from bulk anisotropic hot-deformed MAGNEQUENCH (MQ) magnets. Hydrogen (H) content and x-ray diffraction measurements clarify the effects of H and desorption temperature (Td) on the intrinsic magnetic anisotropy (IMA) of the Nd2Fe14B-type phase and the nature of the intergranular phases, both of which are crucial for high Hci. The Nd-rich intergranular phase disproportionates during HD, initially forming a microcrystalline Nd-hydride phase, possibly Nd2H5. For Td≤220 °C, H remains in the Nd2Fe14B-type phase, severely degrading the IMA, which causes a low Hci. For 220 °C≤Td≤250 °C, enough H desorbs from the Nd2Fe14B-type phase and the IMA recovers its large prehydrided value, and the microstructure supports a high Hci≤10 kOe in spite of the H disproportionated intergranular phase. Only for Td(approximately-greater-than)250 °C is Hci degraded by the microstructure, corresponding to further H desorption and the microcrystalline Nd-hydride phase becoming well-crystallized NdH2. The NdH2 phase decomposes with continued H desorption and at Td(approximately-greater-than)580 °C recombines to re-form the Nd-rich intergranular phase of prehydrided MQ material. H is completely desorbed above 580 °C and Hci(approximately-greater-than)11 kOe, nearly that of the prehydrided MQ magnets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358298
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  • 3
    Electronic Resource
    Electronic Resource
    Properties of Nd-Fe-B anisotropic powder prepared from rapidly solidified materials (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5293-5295 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anisotropic Nd-Fe-B permanent magnets can be prepared by consolidation and hot forming of melt-spun ribbon material; energy products to 45 MGOe have been obtained by this method. One feature of this type of magnet is that they can be converted into stable powders for subsequent processing into anisotropic resin-bonded magnets. The stability of this powder contrasts markedly with that prepared by grinding conventional "sintered'' magnets, a factor attributed to the much smaller crystallite size of the rapidly solidified materials. In this work the properties of the anisotropic powder are presented along with preliminary properties of bonded magnets; energy products of 15–17 MGOe have been achieved by compression molding techniques and energy product as high as 20 MGOe are believed to be readily achievable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342396
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrogen decrepitated anisotropic Nd-Fe-B powder: Hydrogen desorption and magnetic properties : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6482-6484 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hydrogen decrepitation (HD) process easily pulverizes rapidly solidified, hot-deformed Nd-Fe-B (MQ3) magnets but degrades the magnetic properties. Recovery of high-performance magnetism in HD MQ3 powder has always required hydrogen desorption at temperatures above 600 °C. It is reported that desorption at the relatively low temperature of 240 °C restores magnetic coercivity Hci to above 10 kOe despite residual hydrogen in the material. Desorption between 240 and 580 °C significantly degrades Hci but not the intrinsic magnetic anisotropy. Hydrogen is reabsorbed when the desorbed powder is cooled from above 600 °C to room temperature in the presence of small amounts of residual hydrogen gas. This hydrogen reabsorption strongly degrades the coercivity but does not affect the intrinsic magnetic anisotropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352587
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  • 5
    Electronic Resource
    Electronic Resource
    Pulverizing anisotropic rapidly solidified Nd-Fe-B materials for bonded magnets : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6603-6605 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high (BH)max potential of Nd-Fe-B materials make them excellent candidates for bonded magnets. We have previously shown that anisotropic bonded magnets can be made from hot deformed rapidly solidified materials. The purpose of this paper is to show how hot deformed materials can be pulverized into desired particle size ranges by using specific hydrogen decrepitation (HD) cycles. Specific temperatures for hydriding and desorbing cycles to achieve desired particle size ranges and magnetic values are given. The data shows that there are optimum times and temperatures to achieve the desired magnetic properties. TEM and SEM photomicrographs of mechanically and HD pulverized materials are shown. TEM studies show that stacking faults generated during HD are relieved after desorption. With proper control of HD and desorption, bonded magnets have been produced having (BH)max values as high as 18.9 MGOe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349871
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen absorption and disproportionation of melt-spun Nd–Fe–B ribbons (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3514-3518 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogen absorption and disproportionation of melt-spun Nd–Fe–B-based ribbons are significantly affected by quench state (wheel speed). The initial hydrogen absorption temperature corresponding to the formation of the Nd2Fe14BHx-type phase shifts from ∼120 °C for ingot to 250–300 °C for ribbons spun at 13, 15, 17, 20, 22, and 24 m/s wheel speeds. This shift is presumably related to the fact that ribbons are considerably more inert than ingot, which is typical of Nd–Fe–B materials. The hydrogen disproportionation temperature, however, monotonically decreases with increasing wheel speed from (approximately-greater-than)700 °C for ingot to 530 °C for 24 m/s ribbons. Hydrogen absorption due to disproportionation exhibits a two-step feature for wheel speeds ≥20 m/s. The onset and size of the lower temperature step correlates with the presence and amount of an amorphouslike component in the x-ray diffraction spectra of as-spun ribbons. The amorphouslike component is detectable only for wheel speeds ≥20 m/s, and both the amount of amorphouslike component and the size of the lower temperature step in the hydrogen absorption increase with increasing wheel speed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355317
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of additive elements on magnetic properties and irreversible loss of hot-worked Nd-Fe-Co-B magnets : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6049-6051 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There has been limited work on the effects of alloying elements on the properties of hot-worked anisotropic magnets. The coercivity mechanisms for sintered and rapidly solidified Nd-Fe-B magnets are different, and additives can have different effects on magnetic properties. The present study was conducted to clarify the effects of various alloying elements on the properties of hot-worked magnets. Ribbons of composition (Nd13.6−xRx)(Fe77.6−yTyCo2.8)B6.0 (R=Ce and Dy; T=Al, V, Cu, Ga, Zr, Nb, Mo, and Sn; x=0, 1, and 2; y=0, 0.5, and 1.0) were prepared by melt spinning. Anisotropic magnets were made at 1073 K with 55.6% reduction in height by die upsetting. Room-temperature magnetic properties and irreversible losses after exposure at 323–473 K were determined. The results showed that small amounts of Al, V, Cu, and Ga enhanced the remanence of the magnets, while Dy, Al, Ga, Zr, Nb, and Mo improved the coercivity. Dy, Ga, and Mo additions were effective in increasing the heat resistance temperature (HRT), defined as the temperature where the irreversible loss is 3%. HRT is dependent on initial intrinsic coercivity and the squareness ratio (Hk/iHc) of the demagnetization curve. An equation relating these parameters is given. An HRT of 453 K was obtained with a suitable alloy composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347766
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  • 8
    Electronic Resource
    Electronic Resource
    Microstructure of high-remanence Nd-Fe-B alloys with low-rare-earth content : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6652-6654 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure and magnetic properties of bonded and fully dense magnets produced from melt-spun ribbons of the composition RE4.5TM76Ga1B18.5 have been investigated, where RE refers to a mixture of Nd and Dy, and TM refers to a mixture of Fe and Co. Results show that annealing overquenched ribbons with about 3 wt. % Dy and 3 wt. % Co at 700 °C can produce materials with Hci(approximately-equal-to)4 kOe, Br(approximately-equal-to)11.5 kG, and (BH)max(approximately-equal-to)14.5 MGOe, the latter being comparable to those of commercial ribbons containing three times as much Nd. The microstructure of annealed ribbons consists of about 30% Nd2Fe14B grains, 65% Fe3B grains, and 5% α-Fe grains. The grains of all the phases are nearly spherical. The grain diameters are in the 30–50 nm range. Hot-pressed magnets made from overquenched ribbons are fully isotropic, with magnetic and microstructural characteristics similar to those of the annealed ribbons. The high remanence and low coercivity correlate well with the microstructure consisting of a uniform mixture of the hard Nd2Fe14B phase and soft α-Fe and Fe3B phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356884
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  • 9
    Electronic Resource
    Electronic Resource
    The microstructure of hot formed neodymium–iron–boron magnets with energy product 48 MG Oe : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6470-6472 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Melt-spun Nd–Fe–B ribbons containing small amounts of Co, Ga, and C were die upset to 60% and 70% reduction in height in an argon atmosphere between 750 and 800 °C. The magnet, which was die upset 70%, has a remanence of 14.2 kG, Hci of 14.8 kOe, and (BH)max of 48 MG Oe. The interior of the magnet consists of well-aligned Nd2Fe14B grains separated by a Nd-rich intergranular phase. Intermixed with such aligned grains, we observed zones of unaligned fine-grained material without any intergranular phase. Since the intergranular phase is a key factor for deformation and alignment and it is uniformly distributed in the hot pressed precursor, it will be possible to enhance the alignment further by controlling the redistribution of the intergranular phase during die upsetting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352583
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  • 10
    Electronic Resource
    Electronic Resource
    Properties of bonded anisotropic magnets : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6465-6467 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-energy product anisotropic Nd-Fe-B permanent magnets can be prepared by consolidation and hot-deforming melt-spun material. One feature of this type of magnet is that it can be converted into stable powders for subsequent processing into anisotropic bonded magnets. The stability of this powder is attributed to the much smaller crystalline size of the rapidly solidified materials compared to that of sintered magnets. In this work, the properties of anisotropic bonded magnets made from powders produced by hydrogen decrepitation and by a mechanical crushing process are given. Energy products of 15–18 MGOe have been achieved by compression molding techniques. Long-term thermal stability at 100 and 125 °C of bonded magnets using various binders are given. Transmission electron microscopy studies of the anisotropic powder indicate the microstructure to be similar to the hot-deformed precursor material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349932
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