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Title: Microstructural and magnetic property evolution with different heat-treatment conditions in an alnico alloy

Abstract

Further property enhancement of alnico, an attractive near-term, non-rare-earth permanent magnet alloy system, primarily composed of Al, Ni, Co, and Fe, relies on improved morphology control and size refinement of its complex spinodally decomposed nanostructure that forms during heat-treatment. Using a combination of transmission electron microscopy and atom probe tomography techniques, this study evaluates the magnetic properties and microstructures of an isotropic 32.4Fe-38.1Co-12.9Ni-7.3Al-6.4Ti-3.0Cu (wt.%) alloy in terms of processing parameters such as annealing temperature, annealing time, application of an external magnetic field, as well as low-temperature “draw” annealing. Optimal spinodal morphology and spacing is formed within a narrow temperature and time range (~840 °C and 10 min) during thermal-magnetic annealing (MA). The ideal morphology is a mosaic structure consisting of periodically arrayed ~40 nm diameter (Fe-Co)-rich rods (α 1 phase) embedded in an (Al-Ni)-rich (α 2 phase) matrix. A Cu-enriched phase with a size of ~3–5 nm is located at the corners of two adjacent {110} facets of the α 1 phase. The MA process significantly increased remanence (B r) (~40–70%) of the alloy due to biased elongation of the α 1 phase along the <100> crystallographic direction, which is closest in orientation to the applied magnetic field. As amore » result, the optimum magnetic properties of the alloy with an intrinsic coercivity (H cj) of 1845 Oe and a maximum energy product (BH max) of 5.9 MGOe were attributed to the uniformity of the mosaic structure.« less

Authors:
 [1];  [1];  [1];  [2];  [2];  [1];  [1]
  1. Ames Lab., Ames, IA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1361376
Alternate Identifier(s):
OSTI ID: 1363632; OSTI ID: 1417110
Report Number(s):
IS-J-9288
Journal ID: ISSN 1359-6454; KC0403040; ERKCZ01
Grant/Contract Number:
AC05-00OR22725; AC02-07CH11358
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 133; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; permanent magnet; alnico; spinodal decomposition; transmission electron microscopy

Citation Formats

Zhou, Lin, Tang, Wei, Ke, Liqin, Guo, Wei, Poplawsky, Jonathan D., Anderson, Iver E., and Kramer, Matthew J. Microstructural and magnetic property evolution with different heat-treatment conditions in an alnico alloy. United States: N. p., 2017. Web. doi:10.1016/j.actamat.2017.05.012.
Zhou, Lin, Tang, Wei, Ke, Liqin, Guo, Wei, Poplawsky, Jonathan D., Anderson, Iver E., & Kramer, Matthew J. Microstructural and magnetic property evolution with different heat-treatment conditions in an alnico alloy. United States. doi:10.1016/j.actamat.2017.05.012.
Zhou, Lin, Tang, Wei, Ke, Liqin, Guo, Wei, Poplawsky, Jonathan D., Anderson, Iver E., and Kramer, Matthew J. Mon . "Microstructural and magnetic property evolution with different heat-treatment conditions in an alnico alloy". United States. doi:10.1016/j.actamat.2017.05.012. https://www.osti.gov/servlets/purl/1361376.
@article{osti_1361376,
title = {Microstructural and magnetic property evolution with different heat-treatment conditions in an alnico alloy},
author = {Zhou, Lin and Tang, Wei and Ke, Liqin and Guo, Wei and Poplawsky, Jonathan D. and Anderson, Iver E. and Kramer, Matthew J.},
abstractNote = {Further property enhancement of alnico, an attractive near-term, non-rare-earth permanent magnet alloy system, primarily composed of Al, Ni, Co, and Fe, relies on improved morphology control and size refinement of its complex spinodally decomposed nanostructure that forms during heat-treatment. Using a combination of transmission electron microscopy and atom probe tomography techniques, this study evaluates the magnetic properties and microstructures of an isotropic 32.4Fe-38.1Co-12.9Ni-7.3Al-6.4Ti-3.0Cu (wt.%) alloy in terms of processing parameters such as annealing temperature, annealing time, application of an external magnetic field, as well as low-temperature “draw” annealing. Optimal spinodal morphology and spacing is formed within a narrow temperature and time range (~840 °C and 10 min) during thermal-magnetic annealing (MA). The ideal morphology is a mosaic structure consisting of periodically arrayed ~40 nm diameter (Fe-Co)-rich rods (α1 phase) embedded in an (Al-Ni)-rich (α2 phase) matrix. A Cu-enriched phase with a size of ~3–5 nm is located at the corners of two adjacent {110} facets of the α1 phase. The MA process significantly increased remanence (Br) (~40–70%) of the alloy due to biased elongation of the α1 phase along the <100> crystallographic direction, which is closest in orientation to the applied magnetic field. As a result, the optimum magnetic properties of the alloy with an intrinsic coercivity (Hcj) of 1845 Oe and a maximum energy product (BHmax) of 5.9 MGOe were attributed to the uniformity of the mosaic structure.},
doi = {10.1016/j.actamat.2017.05.012},
journal = {Acta Materialia},
number = C,
volume = 133,
place = {United States},
year = {Mon May 08 00:00:00 EDT 2017},
month = {Mon May 08 00:00:00 EDT 2017}
}

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  • Further property enhancement of alnico, an attractive near-term, non-rare-earth permanent magnet alloy system, primarily composed of Al, Ni, Co, and Fe, relies on improved morphology control and size refinement of its complex spinodally decomposed nanostructure that forms during heat-treatment. Using a combination of transmission electron microscopy and atom probe tomography techniques, this study evaluates the magnetic properties and microstructures of an isotropic 32.4Fe-38.1Co-12.9Ni-7.3Al-6.4Ti-3.0Cu (wt.%) alloy in terms of processing parameters such as annealing temperature, annealing time, application of an external magnetic field, as well as low-temperature “draw” annealing. Optimal spinodal morphology and spacing is formed within a narrow temperature andmore » time range (~840 °C and 10 min) during thermal-magnetic annealing (MA). The ideal morphology is a mosaic structure consisting of periodically arrayed ~40 nm diameter (Fe-Co)-rich rods (α 1 phase) embedded in an (Al-Ni)-rich (α 2 phase) matrix. A Cu-enriched phase with a size of ~3–5 nm is located at the corners of two adjacent {110} facets of the α 1 phase. The MA process significantly increased remanence (B r) (~40–70%) of the alloy due to biased elongation of the α1α1 phase along the <100> crystallographic direction, which is closest in orientation to the applied magnetic field. Here, the optimum magnetic properties of the alloy with an intrinsic coercivity (H cj) of 1845 Oe and a maximum energy product (BH max) of 5.9 MGOe were attributed to the uniformity of the mosaic structure.« less
  • In this study, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy. During double solution heat treatment, carbon is liberated from the dissolution of MC carbides during the first solution treatment at 1150 °C, and fine MC carbides are precipitated on gamma grain boundaries during the second solution treatment at 1120 °C. Due to the concurrent decrease in carbon solubility and the increase in the contribution of grain boundary diffusion at lower temperatures, the MC carbides on the gamma grain boundaries provide a localized carbon reservoir that aids inmore » M 23C 6 carbide precipitation on gamma grain boundaries during exposure at 760 °C. The γ' phase, which is the key strengthening phase in alloy 740, is incorporated into the alloy microstructure during aging at 850 °C. Finally, the main source of microstructural instability observed during exposure at 760 °C was the coarsening of the γ' phase.« less