Fig. 1. Illustrations of (a) Bs and Fe content for the typical Finemet, Nanoperm and HBNAs; (b) The factors within the processing window (PW) of nanocrystalline alloys.

Fig. 2. Characterization of the as-quenched ribbons prepared with spinning rates (v) of 20-40 m/s. (a) XRD patterns and thickness (d) of the ribbons; (b) DSC traces measured with a heating rate of 40 °C/min.

Fig. 3. TEM bright field images of the as-quenched ribbons. (a) Free surface of the 20 m/s ribbon; (b) After polishing less than 1 μm from the free surface; Insets show the corresponding selected area electron diffraction (SAED) pattern and the illustration of the TEM samples taken from the ribbon; (c) Free surface of the 30 m/s ribbon; (d) High-resolution TEM image of the enlarged view in the box. The yellow rings mark the ordered structure.

Fig. 4. Coercivity (Hc) of the Fe84.75Si2B9P3C0.5Cu0.75 (at.%) nanocrystalline alloy ribbons after annealing (a) at different temperature (TA) for 5 min and (b) at 420 °C for different time (tA).

Fig. 5. TEM bright field images, SAED patterns and grain size distributions from the main part of the nanocrystalline alloy ribbons after optimally annealing at 460 °C for 16 min. (a) 20 m/s; (b) 30 m/s; (c) 40 m/s. The upper illustration shows that TEM samples are taken from the middle layer of the ribbons.

Fig. 6. TEM bright field images from the free surface of the nanocrystalline alloy ribbons after optimally annealing at 460 °C for 16 min. (a) 20 m/s; (b) 30 m/s; (c) 40 m/s; (d) Enlarged view of the box as indicated in (a); (e) SAED pattern; (f) Illustration of the structure evolution for the ribbons with different as-quenched microstructure. TEM samples are taken from the free surface of the ribbons as sketched in the upper part.

Fig. 7. Illustrations of the three types of as-quenched microstructures: (a1) coarse nanocrystallite forms at the beginning of the solidification; (b1) quenched-in small crystals/clusters form in the amorphous transition process; (c1) fully amorphous structure obtained from the fast-quenching process. Illustrations of the structure evolution processes during annealing: (a1, a2) coarse nanocrystallite without an obvious change during the annealing process; (b1, b2) fine grains grow up from the quenched-in crystals/clusters smaller than critical size (D*), where D* represents the steady grains size after annealing; the grain refinement mechanism and nanostructure stability stems from the core-shell like heterostructure, and the yellow circles around the grains represent the depletion induced metalloid element rich interlayer; (c1, c2) fine grains grow up with a nucleation-growth process for the amorphous ribbons. (d) Illustration of the crystallization mechanism with respect to the samples prepared with different PW.