Speaker
Description
Mixing powder materials with distinct properties is a well-established approach to overcoming the limitations of individual powders. In soft magnetic systems, this strategy enhances the compressibility of high-performance but brittle materials, such as FeSi [1], FeSiB [2], and FeSiBCCr [3]. FeSi with $>3$ wt.$\%$ Si is typically mixed with epoxy binders, restricting high-temperature processing and limiting its soft magnetic applications.
This study investigates Fe-$6.5$Si/Fe composites with a phosphate surface layer, focusing on the effects of Fe/FeSi ratios, process additives, and compaction parameters on magnetic properties. Fe-$6.5$Si and Somaloy $700$ (Höganäs AB) were used. Somaloy $700$ (without lubricant) was treated with KH550 surfactant ($6$ wt.$\%$), homogenized with FeSi in ethanol via resonant acoustic mixing (RAM), dried ($60$°C, $3$ hrs.), and uniaxially pressed ($800$ MPa) into cylinders and rings. Heat treatments were performed at $650$°C/$1$ hr. and $700$°C/$5$ min. in N$_2$. Similarly, Somaloy $700$ (with lubricant) was RAM-mixed with FeSi, pressed at 800 and $1500$ MPa, and heat-treated at identical conditions in air.
Resistivity increased with FeSi content in silanized Fe/FeSi, reaching $1.43\times10^{-1}$ $\Omega$cm at $50:50$, while a lubricant-based counterpart achieved only $4.0\times10^{-4}$ $\Omega$cm ($800$ MPa) and $2.46\times10^{-4}$ $\Omega$cm ($1500$ MPa). The highest real permeability ($\mu^{\prime}=72$) was observed in silanized Fe/FeSi $70:30$, whereas pure FeSi exhibited the highest relaxation frequency ($4.2$ MHz, $\mu^{\prime}=57$). Lubricant-enhanced samples achieved higher permeability ($198$ for Fe/FeSi $70:30$ at $1500$ MPa). A $60:40$ Fe/FeSi mix ($800$ MPa) had a relaxation frequency of $12.5$ kHz ($\mu^{\prime}=140$), which decreased to $4.8$ kHz ($\mu^{\prime}=180$) at $1500$ MPa for the $50:50$ composition.
Coercivity trends differed between silanized and lubricated samples. In silanized materials, coercivity decreased with increasing FeSi, reaching 210 A/m at Fe/FeSi 50:50 and 130 A/m for pure FeSi. In contrast, lubricated Fe/FeSi 70:30 exhibited $\sim$300 A/m, and 50:50 reached 350 A/m. These results highlight distinct structure formation mechanisms in lubricant- vs. silane-treated compacts, influencing their functional properties. The findings offer new insights into optimizing Fe and FeSi materials for industrial soft magnetic applications.
Acknowledgements
This work was realized within the frame of the project VEGA 2/0099/24.
References
[1] Z. Zheng et al., “Magnetic properties regulation and loss contribution analysis of FeSi soft magnetic composites doped by carbonyl iron powders,” Journal of Magnetism and Magnetic Materials, vol. 568. Elsevier BV, p. 170423, Feb. 2023. https://doi.org/10.1016/j.jmmm.2023.170423
[2] D. N. Chen et al., “Improving the Magnetic Properties of FeSiB Soft Magnetic Composites by Adding Untreated or Phosphated Fe Powders,” Journal of Magnetics, vol. 24, no. 3. The Korean Magnetics Society, pp. 485–490, Sep. 30, 2019. https://doi.org/10.4283/jmag.2019.24.3.485
[3] J. Liu et al., “Improved high-frequency magnetic properties of FeSiBCCr amorphous soft magnetic composites by adding carbonyl iron powders,” Journal of Non-Crystalline Solids, vol. 605. Elsevier BV, p. 122166, Apr. 2023. https://doi.org/10.1016/j.jnoncrysol.2023.122166
