# Microstructure, Magnetic Properties, and Application of FINEMET-Type Alloys with Co Addition
## 4 Conclusions  
Nanocrystalline Fe3\(\mathrm{\times}\)Co\(\mathrm{Nb}_{3}\mathrm{B}_{13}\mathrm{Cu}_{1}\) (x = 6, 25, 58) alloys, in which some Fe atoms have been replaced with Co atoms and annealed at 750 K for 10 min, can be used successfully as materials for magnetic cores. The investigated materials exhibit excellent soft magnetic properties (i.e., a coercive field of less than 125 A/m, and a saturation magnetic flux density ranging from 0.82 to 0.87 T), which are related to their microstructure, and depend on the exchange coupling between the nanocrystalline \(\alpha\)-FeCo grains of 10-30 nm in diameter embedded in the residual amorphous matrix. It is worth noting that the investigated Fe3\(\mathrm{\times}\)Co\(\mathrm{}_{x}\mathrm{Nb}_{3}\mathrm{B}_{13}\mathrm{Cu}_{1}\) (x = 6, 25, 58) alloys annealed at 750 K for 10 min exhibit very low core losses, which makes them extremely attractive for use in the cores of electromagnetic devices. The shift of the Curie points toward higher temperatures after replacing Fe atoms with Co atoms in FINEMET-type alloys, and this makes them suitable for use in the cores of devices operating at H-class temperatures. Taking into account  
\begin{table}
\begin{tabular}{c c c c} \hline
**Technical Parameters \({}^{*}\)** & \multicolumn{3}{c}{**Reactor Type 2 RTF–50 \(\mu\)H 100 Adc 900 Vdc T40F**} \\ \hline Core material & Fe3\(\mathrm{Nb}_{3}\mathrm{B}_{13}\mathrm{Cu}_{1}\) & Fe2\(\mathrm{\times}\)Co\(\mathrm{}_{6}\mathrm{Nb}_{3}\mathrm{B}_{13}\mathrm{Cu}_{1}\) & Fe5\(\mathrm{Co}_{25}\mathrm{Nb}_{3}\mathrm{B}_{13}\mathrm{Cu}_{1}\) \\ \cline{2-4} Core weight & & 17.8 kg & \\ Flux density & 0.52 T & 0.48 T & 0.48 T \\ Core losses & 168 W & 166 W & 132 W \\ Core temperature rise & 73 K & 72 K & 67 K \\ \hline Winding material & & aluminum sheet 3\(\times\) (0.2 \(\times\) 125 mm) & \\ \cline{2-4} Winding losses & 109 W & 128 W & 126 W \\ Winding temperature rise & 69 K & 70 K & 68 K \\ \hline Number of turns & 30 turns & 32 turns & \\ \hline Air gaps in the core per column & 8 \(\times\) 0.55 mm & 8 \(\times\) 0.65 mm & \\ \hline Core dimensions L \(\times\) B \(\times\) H & & 180 \(\times\) 90 \(\times\) 260 mm & \\ \hline Reactor weight & 20.2 kg & 20.4 kg & \\ \hline Reactor dimensions A \(\times\) B \(\times\) C & & 240 \(\times\) 180 \(\times\) 265 mm & \\ \hline \end{tabular} \({}^{*}\)Choke parameters were calculated using RALE Design System software.  
\end{table}
Table 4: Technical data of chokes obtained in computational simulations.  
the results of measurements and simulations of choke core parameters, the manufactured device uses a core made of Fe\({}_{85}\)Co\({}_{25}\)Nb\({}_{3}\)B\({}_{13}\)Cu\({}_{1}\) alloy. Choke specifications obtained in computational simulations with RALE software using the innovative Core ECO\({}^{\text{TM}}\) bonded multigap choke core system demonstrated the wide applicability of Fe.Co-Nb-B-Cu alloy in DC/DC converters.  
M.H.: conceptualization, methodology, validation, writing--original draft, writing--review and editing. M.L.: investigation, methodology, data curation, formal analysis. A.L.: conceptualization, investigation, methodology, writing--original draft, data curation, formal analysis, visualization. H.L.: data curation, visualization. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.