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

Journal Article · Mon May 08 00:00:00 EDT 2017 · Acta Materialia

DOI:https://doi.org/10.1016/j.actamat.2017.05.012· OSTI ID:1361376

Zhou, Lin ^[1]; Tang, Wei ^[1]; Ke, Liqin ^[1]; Guo, Wei ^[2]; Poplawsky, Jonathan D. ^[2]; Anderson, Iver E. ^[1]; Kramer, Matthew J. ^[1]

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1. Ames Lab., Ames, IA (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

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 (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.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC05-00OR22725; AC02-07CH11358
• OSTI ID: 1361376
• Alternate ID(s): OSTI ID: 1363632; OSTI ID: 1417110
• Report Number(s): IS-J-9288; KC0403040; ERKCZ01
• Journal Information: Acta Materialia, Vol. 133, Issue C; ISSN 1359-6454
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
permanent magnet
alnico
spinodal decomposition
transmission electron microscopy