Y.H. Li, G.Z. Zhang, L.C. Wu, W. Zhang. J Mater Sci., 2021, 56:2572–2583.

Abstract:

The effects of annealing temperature and heating rate on the microstructure, magnetic, and mechanical properties of melt-spun Fe_81.7−xSi₄B₁₃Cu_1.3Nb_x (x = 0–4) alloy ribbons have been investigated. With increasing the annealing temperature, a ductile–brittle transition occurs during amorphous structure relaxation, the brittleness becomes severe with more α-Fe precipitation, and the hardness rises continuously. After annealing at respective optimum temperatures under the heating rate of 20 K/min, as the Nb content increases from 0 to 4 at.%, average grain size (D_α-Fe) and volume fraction (V_α-Fe) of the α-Fe in the nanocrystalline alloys decrease gradually from 53.3 nm and 52% to 8.7 nm and 42%, respectively; the strain at fracture (ε_f) representing ductile level increases from 1.33 to 1.72%; and the coercivity (H_c), saturation magnetic flux densities (B_s), and Vickers hardness (H_v) all decrease gradually. As the heating rate rises from 10 to 400 K/min, the D_α-Fe of the Fe_81.7Si₄B₁₃Cu_1.3 alloy decreases from 45.7 to 28.4 nm without considerable variation of the V_α-Fe; the H_c lowers from 235 to 25 A/m, the ε_f increases from 1.10 to 1.66%, and the B_s and H_v change slightly. Enriching of Nb weakens the dependence of nanostructure, magnetic softness, and annealing embrittlement on the heating rate. A correlation of ε_f ∝ D_α-Feⁿ is found for the nanocrystalline alloys, where the n rises from − 1 to − 1/2 with enriching of Nb from 0 to 4 at.%. The mechanisms by which nanostructure affects magnetic and mechanical properties have been discussed.

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