PSI - Issue 40

N. Nikul’chenkov et al. / Procedia Structural Integrity 40 (2022) 354–358 N. Nikul'chenkov et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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cores are successfully used both in conventional (50 Hz) and high-frequency (400 - 10000 Hz) transformers (see Li et al. (2008)). There is a relationship between the size of crystallites and magnetic properties in alloys, the structure of which is formed in the amorphous state during solidification. The grain size decreasing increases the coercivity due to the density of defects increases (the volume fraction of grain boundaries). Weakening of the macroscopic magnetic anisotropy occurs if the grain size is less than the length of the magnetic exchange-correlation due to grain-to-grain interaction. In this case, the coercive force decreases with decreasing grain size (see Herzer (1997)). Fe-based Finemet-type amorphous ribbons have a composition that makes it possible to obtain a nanocrystalline state by heat treatment in a certain temperature range (see Huang et al. (2017), Zhai et al. (2018), Yoshizawa and Takeuchi (1990) and Nikul’chenkov et al. (2019)) . The nanocrystalline structure of Finemet alloys has a significantly better combination of magnetic properties in comparison to the amorphous state: high permeability μ, low coercive force H C , increased induction B S (see Yoshizawa et al. (1988), Zhu (2019) and Starodubtsev (2011)). It is important to anneal the product without going into the recrystallization temperature range significantly worsened magnetic properties of the material due to a decrease in the structure dispersion. This work is devoted to the metallographic determination of the crystallite sizes of the initially amorphous soft magnetic alloy Fe 72.5 Cu 1 Nb 2 Mo 1.5 Si 14 B 9 in the nanocrystalline and recrystallized states and its comparison with the results of modeling based on the results of X-ray diffraction analysis. 2. Material and methods The object of the study was industrial soft magnetic alloy Fe 72.5 Cu 1 Nb 2 Mo 1.5 Si 14 B 9 ( see Tsepelev et al. (2017) and Nikul’chenkov et al. (2019)) . The sample was amorphous precursor as a tape 20 μ m thick and 10 mm wide prepared by melt spinning technique. Non-ambient x-ray diffraction (XRD) with heating in the chamber was used to determine the temperature range of amorphous, nanocrystalline, and recrystallized states (see Nikul’chenkov et al. (2019)) . The pieces of ribbon were annealed at 550 °C and 700 °C with a holding time of 20 minutes to obtain the nanocrystalline and the recrystallized state following x-ray diffraction results. The chamber vacuum furnace was used for annealing. The annealing results were verified by XRD at room temperature (Fig. 1).

Fig. 1. Diffraction patterns for three states of the alloy (amorphous, recrystallized, nanocrystalline) at different annealing temperatures: amorphous - 25 ° C; nanocrystalline - 550 ° С; recrystallized - 700 ° С . XRD was carried out on a Bruker ASX ADVANCE D8 setup in K α Cu radiation ( λ = 1.54 ∙ 10 -10 m). The sizes of the coherent scattering regions (CSRs) were determined used by XRD data.