Soft Magnetic Properties and Wide Supercooled Liquid Region of Fe–P–B–Si Base Amorphous Alloys

Abstract

The glass transition phenomenon was observed in the temperature range before crystallization for amorphous Fe₈₀(P, B, Si)₂₀ alloys. The temperature interval of the supercooled liquid region (ΔT_x) is defined by the difference between glass transition temperature (T_g) and crystallization temperature (T_x) and the largest ΔT_x(=T_x−T_g) value is 36 K for Fe₈₀P₁₂B₄Si₄ where the crystallization reaction takes place through a single stage. The ΔT_x value increases by the dissolution of Al and/or Ga and the largest value is 46 K for Fe₇₆Al₄P₁₂B₄Si₄ and 49 K for Fe₇₄Al₄Ga₂P₁₂B₄Si₄. The effectiveness of additional Al and/or Ga elements is interpreted to result from the formation of a higher degree of dense random packed structure by dissolving the Al and Ga elements with larger atomic sizes. These Fe-based amorphous alloys exhibiting the glass transition phenomenon crystallize through a single-stage exothermic reaction due to the precipitation of five crystalline phases α-Fe, Fe₃B, Fe₂B, Fe₃P and FeP. The long-range atomic rearrangement necessary for the nearly simultaneous precipitaion of the five crystalline phases seems to cause the appearance of the supercooled liquid region through the retardation of the precipitation reaction. The Fe-based amorphous alloys exhibit good soft magnetic properties of 1.14 to 1.34 T for saturation magnetization, 1.1 to 6.4 A/m for coercive force and 19000 to 22000 for permeability at 1 kHz in the annealed state for 600 s at 723 K. The synthesis of the Fe-based amorphous alloys exhibiting good soft magnetic properties and a wide supercooled liquid region is important for future development of a new type of soft magnetic material.