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  • 1
    Electronic Resource
    Electronic Resource
    Effect of microstructure on the corrosion behavior of NdFeB and NdFeCoAlB magnets : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6348-6350 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have previously shown that the corrosion behavior of ternary NdFeB magnets is affected by their oxygen, carbon, and nitrogen contents. The corrosion was measured in autoclaves which give accelerated testing environments of high heat and humidity. In this study, we relate this corrosion behavior in both NdFeB and NdFeCoAlB magnets to effects upon their microstructure. When the oxygen and carbon contents are low in ternary NdFeB magnets, a thick Nd-rich phase (α-Nd and/or NdOx) forms along grain boundaries and their triple junctions. As the oxygen and carbon contents increase, the Nd-rich coating along the boundaries becomes thinner and agglomerates into the triple junctions. With thin grain boundaries, the pathways for corrosion propagation are hindered, thus improving corrosion resistance. With increases in oxygen, the α-Nd and unstable NdOx are changed to stable Nd2O3. Nitrogen increases also aid in the process of conversion to Nd2O3 which leads to better corrosion resistance. Two different features are seen in the microstructure of NdFeCoAlB magnets. The grain boundary phase (Nd3Co) is very stable. Any oxygen in the system appears as fully oxidized Nd2O3. Easily corroded α-Nd and NdOx are not detected. All of these factors combine to produce excellent corrosion resistance in this variety of NdFeCoAlB magnets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349938
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  • 2
    Electronic Resource
    Electronic Resource
    Abnormal grain growth in sintered Nd-Fe-B magnets (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4629-4631 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Abnormal grain growth was found in sintered Nd-Fe-B magnets which are made from powder milled after hydrogen decrepitation. The abnormal grain size in the magnets sintered at 1000 °C for 1.5 h was as large as 400 μm. The formation of abnormally large grains reduced the magnetic properties. As sintering temperature increased, the number of large grains increased and coercivity reduced. However, abnormal grain growth was rarely found when the magnets were fabricated without hydrogen decrepitation. A grain growth mechanism is discussed in relation to the effect of hydrogenation and sintering process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346071
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  • 3
    Electronic Resource
    Electronic Resource
    Hydrogen induced corrosion mechanism in NdFeB magnets : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4840-4842 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation was conducted comparing the corrosion behavior of NdFeB magnets in flowing hydrogen and in the heat and humidity of an autoclave. The results show that corrosion is both macroscopically and microscopically similar in both environments. In both cases, the corrosion progressed most rapidly in those areas where the magnetic orientation of the Nd2Fe14B matrix grains was perpendicular to the outer surface. A corrosion mechanism involving the reaction of hydrogen—either as a pure gas or as a by-product of the decomposition of water vapor—with the neodymium-rich grain boundary phase is proposed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361626
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  • 4
    Electronic Resource
    Electronic Resource
    Relation of remanence and coercivity of Nd,(Dy)-Fe,(Co)-B sintered permanent magnets to crystallite orientation : 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. 6265-6267 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For sintered permanent magnets based on Nd2Fe14B having magnetically oriented crystallites, a simple method of measuring the degree of alignment by x-ray diffraction is described, using the inverse pole figure technique. The results are related to a distribution function for the easy axis which is a direct measure of remanence. The fraction of the ideal [001] texture component in both Nd-Fe-B and Nd,Dy-Fe,Co-B magnets is enhanced by doping with oxygen, resulting in a measurable increase in remanence and improved loop squareness. The observed increase of the intrinsic coercivity iHc with better crystallite orientation is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358300
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  • 5
    Electronic Resource
    Electronic Resource
    High performance NdFeB magnets (invited) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5035-5039 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Although the production and applications of NdFeB magnets have increased enormously in the last decade because of their outstanding magnetic properties at room temperature, some applications were limited because of poor thermal stability and corrosion resistance. To address these problems, there have been many efforts and much progress. In many instances, the alloy modifications produced an improvement of some characteristics but only at the expense of other characteristics. It is therefore necessary to find a method (or alloy) for improving the thermal stability, coercivity, and corrosion resistance without sacrificing performance. We have found that the proper control of very small amounts of Cu, Co, and O in (Nd, Dy)FeB alloys substantially improves the coercivity, high-temperature capabilities, and corrosion resistance without a reduction of remanence. As a result, a high performance NdFeB magnet with excellent temperature stability and corrosion resistance was developed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361566
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  • 6
    Electronic Resource
    Electronic Resource
    High temperature stability of SmTM magnets : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6715-6717 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To meet the demand for permanent magnet materials usable up to 450–500 °C, we investigated and reported that a SmTM magnet with a low temperature coefficient of coercivity and a moderately high coercivity has substantially lower irreversible losses at elevated temperatures than conventional Sm2TM17 magnets. We have continued our studies on the high temperature magnetic behavior of these magnets. The magnetic properties, particularly coercivity, of the SmTM7 alloy magnets are reduced much more slowly than the Sm2TM17 alloy magnets as temperature increases. As a result, the Hci of SmTM7 remains greater than 5 kOe at 500 °C and thus maintains its high-energy product, while the Sm2TM17 magnet has only about 1.7 kOe at the same temperature and has a low energy product. SmTM7 alloy magnets undergoing a long-term stability test at 500 °C exhibit irreversible flux losses of less than 5% after 1240 h. These results indicate that SmTM7 alloy magnets can be usable up to 500 °C for an extended period of time. This will expand the application temperature range of high performance permanent magnets. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367936
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of Al substitution on the coercivity of Nd-Fe-B magnets (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5568-5570 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of Al on the coercivity of Nd-Dy-Fe(Al)B magnets has been investigated with magnetic measurements, differential scanning calorimetry, and microstructure studies. The Al containing samples were found to have a much higher coercivity, a relatively steeper initial magnetization, a different Hc(Hef) curve, and a larger temperature coefficient of coercivity than the samples without Al. Morphology studies made with a scanning transmission electron microscope did not show any significant differences between the two samples. The only evident difference, found in x-ray and electron diffraction data, was in the c/a ratio of the Nd2Fe14B tetragonal phase which was higher for the sample with Al. Another difference was observed in the magnetization reversal mechanism. In the Al-containing samples the magnetization is reversed by changing the magnetization of entire grains, while for the samples without Al the magnetization is reversed by dividing into domains inside the grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342309
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic properties of NdDyFeCoAlB alloys (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3975-3977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature stability of Nd-Fe-B alloy has been improved by the combined addition of Dy and Co and either Al, Ga, or Nb. However, additions of large amounts of Dy, Al, Ga, and Nb substantially reduce the Br from that of Nd-Fe-B, and thus reduce overall magnet performance. This study shows that properly combined additions of Dy, Co, and Al to pseudoternary (Nd,Dy)-(Fe,Co,Al)-B compounds improve both temperature stability and energy density. Hci and Br increase more than in the alloys modified with Dy, Co, or Al alone. The Hci of the alloys increases almost linearly with Dy content at a rate of about 6.8 kOe/at. % Dy, when the alloys contain approximately 5–6 at. % Co, and Al and Dy in a ratio of 1 to 1.2 Al/Dy. The temperature coefficients of Br and Hci, and the irreversible losses of (Nd,Dy)-(Fe,Co,Al)-B alloys are lower than those of the other alloys tested. When compared to Nd-Dy-Fe-Co-B alloy, the reduced consumption of Dy increases the energy products and reduces the material cost, without sacrificing temperature stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340568
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of oxygen on magnetic properties of Nd-Fe-B magnets (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5571-5573 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oxygen plays a very important role in the magnetic properties of R-Fe-B-type alloys. As the oxygen content increases in Nd-Fe-B and Nd-Dy-Fe-Al-B alloys, the alloys gradually lose their magnetic and thermomagnetic properties: the Hci decreases and both the temperature coefficient of Hci and the irreversible temperature loss increase. The degradation of thermomagnetic properties may be accounted for by depletion of the Nd-rich phase in the grain boundaries through Nd oxidation. High coercivity magnets, relatively stable with respect to temperature, can be produced by minimizing the oxygen content in R-Fe-B alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342284
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  • 10
    Electronic Resource
    Electronic Resource
    High coercivity Nd-Fe-B magnets with lower dysprosium content (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3519-3521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The elements Dy and Al play very important roles in the magnetic properties of Nd-Fe-B base compounds. The proper combination of Dy and Al may provide a significant improvement in the magnetic properties. With this in mind, close examinations have been made of the magnetic properties of several (Nd,Dy)-(Fe,Al)-B alloys. As a result, (Nd,Dy)-(Fe,Al)-B alloys containing equal atomic amounts of Dy and Al have been found to provide superior permanent magnetic properties. When compared to Nd-Dy-Fe-B or Nd-Fe-Al-B alloy of equivalent Dy or Al content, they have a much higher Hci . The reduction in Br associated with the addition is markedly less. The Hci of the alloys increases linearly with Dy content at a rate of about 7.5 kOe/at. % Dy, when the alloys contain equal atomic amounts of Dy and Al; or, approximately 1.4× the rate of (Nd,Dy)-Fe-B alloys. When Al is present, much less Dy is required to reach a given coercivity level. Thus, a magnet with high (BH)max and Hci can be more economically produced with Nd-Dy-Fe-Al-B alloys. The small Al additions, as described above, result in higher coercivities and lower irreversible losses at elevated temperatures without increasing temperature coefficients, and thus extend the application temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340728
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