Atom probe tomography study of ultrahigh nanocrystallization rates in FeSiNbBCu soft magnetic amorphous alloys on rapid annealing

Since their introduction over two decades ago, nanostructured soft magnetic alloys have demonstrated excellent magnetic softness and improved performance over a wide range of environmental conditions. This chapter gives an updated account of progress in alloy design, synthesis, structure, and performance of this class of alloys. Existing data are reviewed to highlight recent advances and promote new perspectives for future work in this area.

Nanocrystalline Soft Magnetic Alloys Two Decades of Progress

Metallic glasses (MGs) inherit their amorphous structure from the liquid state, which predetermines their ability to withstand high loads approaching the theoretical limit. However, the absence of slip systems makes them very sensitive to the type of loading and extremely brittle in tension. The latter can be improved by precipitation of ductile crystals, which suppress a catastrophic propagation of shear bands in a glassy matrix. Here we report a novel approach to obtain MG-matrix composites with tensile ductility by flash Joule heating applied to Cu47.5Zr47.5Al5 (at.%) metallic glass. This homogeneous, volumetric and controllable rapid heat treatment allows achieving uniformly distributed metastable B2 CuZr crystals in the glassy matrix. It results in a significant tensile strain of 6.8±0.5%. Moreover, optimized adjustment of the heat-treatment conditions enables tuning of microstructure to achieve desired mechanical properties.

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Flash Joule heating for ductilization of metallic glasses

The rapid thermal processing (RTP) technique features dynamic control of temperature, which permits high heating and cooling rates that cannot be reached with conventional furnace treatments. In recent years, RTP has been increasingly applied to the processing of magnetic materials. The controllable heating profiles provide an approach for the deliberate construction of materials structure via expediting phase transitions and tailoring materials morphology. In this review, the history, principles and facilities of several types of RTP techniques are introduced, including laser and electron beam heating, lamp heating, Joule heating and pulse thermal processing techniques. RTP of various advanced magnetic materials are reviewed, including soft magnetic materials, spintronic materials, magnetic recording materials and nanocomposite hard magnetic materials. Advantages of RTP are highlighted and compared with conventional thermal treatments.

https://iopscience.iop.org/article/10.1088/0022-3727/39/14/R01/pdf

Rapid thermal processing of magnetic materials

Non-conventional heating treatments, such as Joule heating, can produce materials with attractive physical properties Although extensively explored in amorphous wires and ribbons, one of the major drawbacks of the technique is the intrinsic difficulty in determining the annealing temperature The temperature behaviour of two selected wires submitted to a DC electrical current of increasing amplitude was calibrated by comparing the temperature dependence of the material's saturation magnetization obtained during Joule heating to that measured during conventional annealing in a furnace As a result, a correlation between the average temperature and current density was obtained A theory describing the thermal effects of a continuous current flow in amorphous wires is proposed, showing that the thermal treatment is nearly uniform over the entire wire volume, under typical experimental conditions The effect of fluctuations of the wire diameter on the steady-state temperature is also discussed

M. Barricco

Papers

Soft nanocrystalline ferromagnetic alloys with improved ductility obtained through dc Joule heating of amorphous ribbons