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

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
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  1. Ames Lab., Ames, IA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1359-6454; KC0403040; ERKCZ01
Grant/Contract Number:
AC05-00OR22725; AC02-07CH11358
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 133; Journal Issue: C; Journal ID: ISSN 1359-6454
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)
Country of Publication:
United States
36 MATERIALS SCIENCE; permanent magnet; alnico; spinodal decomposition; transmission electron microscopy
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1363632; OSTI ID: 1417110