Thermodynamic analysis of binary Fe85B15 to quinary Fe85Si2B8P4Cu1 alloys for primary crystallizations of α-Fe in nanocrystalline soft magnetic alloys

Abstract

Fe-based Fe85B15, Fe84B15Cu1, Fe82Si2B15Cu1, Fe85Si2B12Cu1, and Fe85Si2B8P4Cu1 (NANOMET®) alloys were experimental and computational analyzed to clarify the features of NANOMET that exhibits high saturation magnetic flux density (Bs) nearly 1.9 T and low core loss than conventional nanocrystalline soft magnetic alloys. The X-ray diffraction analysis for ribbon specimens produced experimentally by melt spinning from melts revealed that the samples were almost formed into an amorphous single phase. Then, the as-quenched samples were analyzed with differential scanning calorimeter (DSC) experimentally for exothermic enthalpies of the primary and secondary crystallizations (ΔHx1 and ΔHx2) and their crystallization temperatures (Tx1 and Tx2), respectively. The ratio ΔHx1/ΔHx2 measured by DSC experimentally tended to be extremely high for the Fe85Si2B8P4Cu1 alloy, and this tendency was reproduced by the analysis with commercial software, Thermo-Calc, with database for Fe-based alloys, TCFE7 for Gibbs free energy (G) assessments. The calculations exhibit that a volume fraction (Vf) of α-Fe tends to increase from 0.56 for the Fe85B15 to 0.75 for the Fe85Si2B8P4Cu1 alloy. The computational analysis of the alloys for G of α-Fe and amorphous phases (Gα-Fe and Gamor) shows that a relationship Gα-Fe ∼ Gamor holds for the Fe85Si2B12Cu1, whereas Gα-Fe < Gamor for the Fe85Si2B8P4Cu1 alloy at Tx1 and that an extremely high Vf = 0.75 was achieved for the Fe85Si2B8P4Cu1 alloy by including 2.8 at. % Si and 4.5 at. % P into α-Fe. These computational results indicate that the Fe85Si2B8P4Cu1 alloy barely forms amorphous phase, which, in turn, leads to high Vf and resultant high Bs.

Fabrication and Soft Magnetic Properties of Fe81.3Si4B10P4Cu0.7 Amorphous Powders by Using the Spinning-water Atomization Process

“…So far, the largest size of Fe-based amorphous soft magnetic alloy (Fe66Co15Mo1P7.5C5.5B2Si3) have been reported being 2 mm, and its Bs is 1.65 T and ΔT(ΔT = Tx1-Tx2) is only 44 K [10]. Insufficient amorphous forming abilities of the Febased ribbons, usually less than 30 μm, limit their extensive applications [1,5,8]. Electric spark sintering (SPS) method [11] or additive manufacturing (3D printing, selective laser remelting, hot isostatic pressing, etc.)…”

Combined machine learning and CALPHAD approach for discovering processing-structure relationships in soft magnetic alloys

“…In addition, composition variations and processing parameters (e.g., heat treatment schedule) play an integral role in modeling the microstructure(s) responsible for achieving desired properties, where optimizing processing parameters along with composition remains a challenging task. 21 As an alternative to costly experimentation, the CALPHAD approach allows for investigating the effect of composition variations and heat treatment on the size distribution and volume fraction of the phase(s) that are responsible for optimal or desired properties; indeed, it has been used for studying soft magnets containing amorphous phases [22][23][24] using the commercial software Thermocalc. 25 Recent studies indicate that simulations based on CALPHAD 26,27 are in need of efficiency improvements if they are to be used for optimization of the composition and heat treatment schedule.…”