Speaker
Description
Iron-based alloy systems Fe–(Al, Ga)–(P, C, B) rank among the softest magnetic materials obtained through controlled annealing (Hc ≈ 1.3 A/m annealed at 713 K ≈ 0.97Tg) to relieve internal stresses, i.e., after optimum relaxation of the amorphous structure. Low coercivity stems from the suppression of the formation of crystal nuclei of the iron and iron-metalloid compounds. High phosphorus (P) content in the iron-based alloy system inhibits the rapid growth of α-Fe grains during the crystallization process. The solubility of gallium (Ga) in the iron matrix that causes structural expansion, combined with its immiscibility with carbon (C) and boron (B), alters the nature of the bonds between Fe and the elements B or C, leading to a reduction in the preferential precipitation of the $Fe_{3}B$, $Fe_{2}B$, and $Fe_{3}C$. Alloying with other Fe-miscible elements, such as aluminum (Al), which has a similar atomic radius to Ga, brings advantages including good ductility, processability, and lower material costs.
Master alloy of chemical compositions $Fe_{72}Al_{5}Ga_{2}P_{11}C_{6}B_{4}$ was prepared by arc-melting in Ti-gettered argon atmosphere to prevent oxidation and nitrogen contamination. The ribbons produced by a single-roller melt-spinning technique in air exhibit as-cast ‘‘XRD-amorphous’’ state. Elemental SEM-EDS mapping confirmed the presence and homogeneous distributions of all constituent elements of the alloy. Areas of increased roughness were observed on the ribbon's shiny side, resulting from a large number of gas bubbles trapped between the liquid pool and the copper wheel. During magnetization, these areas act as pinning centers on the magnetic domain walls, thereby disrupting low coercivity and high permeability.
The DSC trace exhibits a glass-transition region followed by an exothermic crystallization process (at a heating rate of 40 K/min, the onset of the glass transition and crystallization is Tg = 736 K, Tx = 802 K, respectively). The higher heating rate causes a thermal lag and shifts the crystallization peak temperature from 788 K (10 K/min) to 813 K (50 K/min). The observed supercooled liquid region ΔTx = Tx – Tg ≈ 66 K is a metastable temperature interval where the alloy remains a highly viscous, disordered liquid. After annealing at 973 K, many peaks are present in the XRD pattern. Since they overlap, it is not easy to identify all the phases present. XRD confirmed the formation of the clearly visible bcc-Fe and iron-boron $Fe_{2}B$ phase.
Acknowledgement
The authors acknowledge the joint support by the Slovak Research and Development Agency and Serbian Ministry for Science, Technological Development, and Innovations (Project: New Perspective in Amorphous and Nanocrystalline Soft Magnetic Alloys – NewAM – Grant No. APVV SK-SRB- 25-0003), as well as support under the Project Multimodal Approach to Study Structure-Property Relationships in Advanced Materials (MASSPRAM), co-financed by the NextGenerationEU fund.
