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Title: Texture development and coercivity enhancement in cast alnico 9 magnets

Authors:
 [1]; ORCiD logo [2];  [2]; ORCiD logo [2];  [1]; ORCiD logo [3];  [3];  [3];  [4];  [1]
  1. Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588, USA, Nebraska Center for Materials and Nanoscience (NCMN), University of Nebraska, Lincoln, NE 68588, USA
  2. Nebraska Center for Materials and Nanoscience (NCMN), University of Nebraska, Lincoln, NE 68588, USA
  3. Ames Lab, Iowa State University, Ames, IA 50011, USA
  4. Nebraska Center for Materials and Nanoscience (NCMN), University of Nebraska, Lincoln, NE 68588, USA, Department of Mechanical and Materials Engineering, University of Nebraska, Lincoln, NE 68588, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1414985
Grant/Contract Number:
AC02-07CH11358
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
AIP Advances
Additional Journal Information:
Journal Volume: 8; Journal Issue: 5; Related Information: CHORUS Timestamp: 2017-12-27 12:21:03; Journal ID: ISSN 2158-3226
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English

Citation Formats

Zhang, Wenyong, Valloppilly, Shah, Li, Xingzhong, Yue, Lanping, Skomski, Ralph, Anderson, Iver, Kramer, Matthew, Tang, Wei, Shield, Jeff, and Sellmyer, David J. Texture development and coercivity enhancement in cast alnico 9 magnets. United States: N. p., 2018. Web. doi:10.1063/1.5007171.
Zhang, Wenyong, Valloppilly, Shah, Li, Xingzhong, Yue, Lanping, Skomski, Ralph, Anderson, Iver, Kramer, Matthew, Tang, Wei, Shield, Jeff, & Sellmyer, David J. Texture development and coercivity enhancement in cast alnico 9 magnets. United States. doi:10.1063/1.5007171.
Zhang, Wenyong, Valloppilly, Shah, Li, Xingzhong, Yue, Lanping, Skomski, Ralph, Anderson, Iver, Kramer, Matthew, Tang, Wei, Shield, Jeff, and Sellmyer, David J. 2018. "Texture development and coercivity enhancement in cast alnico 9 magnets". United States. doi:10.1063/1.5007171.
@article{osti_1414985,
title = {Texture development and coercivity enhancement in cast alnico 9 magnets},
author = {Zhang, Wenyong and Valloppilly, Shah and Li, Xingzhong and Yue, Lanping and Skomski, Ralph and Anderson, Iver and Kramer, Matthew and Tang, Wei and Shield, Jeff and Sellmyer, David J.},
abstractNote = {},
doi = {10.1063/1.5007171},
journal = {AIP Advances},
number = 5,
volume = 8,
place = {United States},
year = 2018,
month = 5
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.5007171

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  • Nd-Fe-B as-cast alloys in the form of small ingots 4--5 mm thick and with composition Nd{sub 2.1}Fe{sub 14}B were transformed into high coercivity magnets using the hydrogenation disproportionation desorption (HDD) process without decrepitation of the blocks taking place. Magnetic measurements revealed that it was possible to produce blocks with coercivity of {similar to}780 kA m{sup {minus}1}, remanence of {similar to}680 mT and a {ital BH}{sub max} of {similar to}68 kJ m{sup {minus}3} (8.6 MGOe). The high coercivities in these samples were attributed to the disproportionation and subsequent recrystallization process. SEM metallographs of the samples processed at optimum temperature revealed anmore » absence of the original large ({similar to}200 {mu}m) grains of Nd{sub 2}Fe{sub 14}B containing areas of free iron; instead an extremely fine grained, submicron, microstructure of single phase Nd{sub 2}Fe{sub 14}B grains was observed. In samples processed at temperatures higher than that found to be the optimum, larger Nd{sub 2}Fe{sub 14}B grains with extremely rectangular morphologies could be observed growing from surrounding submicron matrix grains. Domain patterns observed on these larger grains, using the Kerr effect, indicated that Nd{sub 2}Fe{sub 14}B matrix grains appear to grow predominantly with rectangular morphologies from the disproportionated material with the {ital a} and {ital c} crystal axis running parallel to the edges of the rectangle.« less
  • The 2011 price shock in the rare earth (RE) permanent magnet (PM) marketplace precipitated realization of extremely poor RE supply diversity and drove renewed research in RE-free permanent magnets such as “alnico.” Essentially, alnico is an Al-Ni-Co-Fe alloy with high magnetic saturation and T C, but low coercivity. It also was last researched extensively in the 1970’s. Currently alnico “9” magnets with the highest energy product (10MGOe) are manufactured by directional solidification to make highly aligned anisotropic magnets. This work developed novel powder processing techniques to improve on unaligned anisotropic alnico “8H” with elevated coercivity. Gas atomization was used tomore » produce pre-alloyed powder for binder-assisted compression molding of near-final shape magnets that were vacuum sintered to full density (<1% porosity). Biased grain growth with resulting grain alignment was achieved during a second solution annealing step, during which a uni-axial stress was applied along the axis parallel to the magnetization direction. Lastly, evaluation of heavily stressed samples (>250g) showed reduced overall loop squareness compared to unaligned (equiaxed) 8H due to grain rotation-induced misalignment, while low stresses improved squareness and greatly improved alignment compared to equiaxed magnets, with squareness approaching 0.30 and remanence ratio as high as 0.79.« less
    Cited by 1
  • The 2011 price shock in the rare earth (RE) permanent magnet (PM) marketplace precipitated realization of extremely poor RE supply diversity and drove renewed research in RE-free permanent magnets such as “alnico.” Essentially, alnico is an Al-Ni-Co-Fe alloy with high magnetic saturation and T C, but low coercivity. It also was last researched extensively in the 1970’s. Currently alnico “9” magnets with the highest energy product (10MGOe) are manufactured by directional solidification to make highly aligned anisotropic magnets. This work developed novel powder processing techniques to improve on unaligned anisotropic alnico “8H” with elevated coercivity. Gas atomization was used tomore » produce pre-alloyed powder for binder-assisted compression molding of near-final shape magnets that were vacuum sintered to full density (<1% porosity). Biased grain growth with resulting grain alignment was achieved during a second solution annealing step, during which a uni-axial stress was applied along the axis parallel to the magnetization direction. Lastly, evaluation of heavily stressed samples (>250g) showed reduced overall loop squareness compared to unaligned (equiaxed) 8H due to grain rotation-induced misalignment, while low stresses improved squareness and greatly improved alignment compared to equiaxed magnets, with squareness approaching 0.30 and remanence ratio as high as 0.79.« less
  • Cited by 1
  • Small addition of boron nitride is effective in increasing the Hci value of Nd-Fe-B magnets. With the optimal addition of 0.1 wt% BN, a maximum 20% increase in Hci and a slight increase in Br are obtained, hence (BH)m is slightly enhanced. Chemical compositions estimated by Auger spectroscopy and EPMA indicate that the boron concentration is higher at grain boundaries. The higher concentration of boron can be the result that BN particles react with Nd and dissolve in the Nd-rich phase during the heating processes. Although the dissolved BN contributes to slight grain refining, the coercivity mechanism might be attributedmore » to the change in compositions, notably an increase of NdN and NdB{sub 6}, and morphology of the intergranular phase.« less