Research on the effect of P on the microstructure and crystallization mechanism of spherical FeSiBPNbCu nanocrystalline powder

This study establishes a holistic strategy for high-performance Fe 80 Si 5 B (11-x) P x Nb 3 Cu 1 soft magnetic composites (SMCs) through phosphorus(P) alloying design and low-pressure thermal encapsulation molding process(LHP). A spheroidization-solidification competition parameter η (η = t sph /τ) is proposed to quantify morphology evolution, revealing that η ≤ 0.6 achieves >92 % spherical powders (D 50 = 20 μm), while η ≥ 1 induces dendritic defects. Fig. Schematic diagram of internal structure of Fe 80 Si 5 B 8 P 3 Nb 3 Cu 1 powder sample after annealing treatment. The as-quenched Fe 80 Si 5 B 8 P 3 Nb 3 Cu 1 powder form a heterogeneous amorphous matrix due to rapid solidification, resulting in atomic-scale dense-packed and loose regions. Annealing treatment can cause structural relaxation in the amorphous matrix, leading to the diffusion of atoms from the dense region to the loose region. The atomic density in the loose region increases, making the microstructure inside the material more uniform and releasing internal stress. The internal structural evolution process can be summarized into three stages: stress-relief stage and Nanocrystallization stage and secondary phase precipitation stage. • A spheroidization-solidification competition parameter η is proposed to quantify morphology evolution. • When η ≤ 0.6 achieves > 92 % spherical powders, while η ≥ 1 induces dendritic defects. • Annealing optimizes magnetic properties via dual-phase evolution. • Spherical powder combined with LHP enables defect-free monolithic inductors. This study establishes a holistic strategy for high-performance Fe 80 Si 5 B (11-x) P x Nb 3 Cu 1 soft magnetic composites through phosphorus alloying design and low-pressure thermal encapsulation molding process. A spheroidization-solidification competition parameter η is proposed to quantify morphology evolution, revealing that η ≤ 0.6 achieves >92 % spherical powders, while η ≥ 1 induces dendritic defects. P addition tunes η by elevating undercooling and viscosity, enabling precise morphology control. The research indicate that the addition of P enhances glass forming ability by reducing the liquidus temperature and stabilizing the deep eutectic composition, achieving a completely amorphous structure and suppressing the crystallization of α-Fe (Si, B). P-induced Fe-P-B covalent clustering reduces coercivity but slightly lowers saturation magnetization due to disrupted exchange coupling. Annealing optimizes magnetic properties via dual-phase evolution: low-P systems (x ≤ 2) exhibit α-Fe(Si,B) coarsening-driven Hc spikes, while high-P alloys form amorphous/nanocrystalline composites with exchange-spring effects. Cu/Nb synergistically stabilize nanograins and suppress coarsening. Spherical powder combined with LHP enables defect-free monolithic inductors, achieving a 4-fold higher DC breakdown voltage (>1000 V) and 23.8 % improved saturation current compared to cold-pressed counterparts. LHP minimizes residual stress, restricting permeability fluctuations to ≤3 % under thermal stability testing, versus ≥10 % in cold-pressed processes.