A new mechanism for improving electromagnetic properties based on tunable crystallographic structures of FeCoNiSiₓAl₀.₄ high entropy alloy powders
2018
Zhang, Bin | Duan, Yuping | Cui, Yulong | Ma, Guojia | Wang, Tongmin | Dong, Xinglong
Mechanical grinding method was employed to prepare FeCoNiSiₓAl₀.₄ high entropy alloy powders, which present a simple solid solution structure (FCC and BCC). After annealing at 673 K, a large amount of BCC phase precipitate and a small amount of CoFe₂O₄ phase generate. The change of crystal structure may lead to an increase in Mₛ (from 100.3 emu g⁻¹ to 124.2 emu g⁻¹) and a decrease in Hc (from 107 Oe to 59.5 Oe for FeCoNiSi₀.₃Al₀.₄). The silica content has a significant effect on the electromagnetic parameters of the as-milled and as-annealed alloy powders, presenting the trend of first increase and then decrease. And the dielectric constant is obviously improved after annealing (e.g. from 8.48 to 11.21 and from 0.15 to 2.84 for the ε′ and ε′′ of FeCoNiSi₀.₃Al₀.₄ at 18 GHz, respectively), while the permeability is reduced. Compared with those of the as-milled samples, the μ′ of as-annealed FeCoNiSiₓAl₀.₄ (x = 0.1, 0.3, 0.4) remain unchanged or even increase due to the formation of CoFe₂O₄. Meanwhile, the relative content of the precipitated BCC to FCC for FeCoNiSi₀.₃Al₀.₄ enhance with the annealing temperature increase from 573 K to 773 K, and then reduce. And the ε′ and μ′ at 2 GHz present the same trend as the content ratio (ABCC/AFCC), while the ε′′ improve obviously after annealing, corresponding to the elevation of conductivity.
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