New Fe-based amorphous alloys with large magnetostriction and wide supercooled liquid region before crystallization

A glass transition, followed by a supercooled liquid region was found in wide composition ranges of 0–65 at % Co and 1.5–7 at % Ln in Fe_80-x-yCo_xLn_yB₂₀ (Ln=Nd, Sm, Tb, or Dy) amorphous alloys. The supercooled liquid region (ΔT_x) shows the largest value of 41 K for the Fe₄₇Co₃₀Sm₃B₂₀ alloy. An internal equilibrium state leading to the disappearance of the previous thermal history was achieved within a temperature interval of 15 K. The Fe–Co–Ln–B amorphous alloys exhibit soft ferromagnetism with saturated magnetization (B_s) of 0.84–1.66 T and coercivity (H_c) of 5.0–36 A/m. A high magnetostriction (λ_s) exceeding 40×10^-6 was also observed in the composition range of 0–10 at % Co and 1.5–3 at % Ln (Ln=Sm, Tb, or Dy). The highest λ_s reaches 58×10^-6 for Fe_68.5Co₁₀Ln_1.5B₂₀ (Ln=Sm or Tb), which is higher than the highest value (44×10^-6) for previously reported amorphous alloys. All the Fe_68.5Co₁₀Ln1.5B₂₀ amorphous alloys have good bending ductility. The tensile strength, Vickers hardness and Young’s modulus of the Fe_68.5Co₁₀Sm_1.5B₂₀ alloy are 3220 MPa, 990 and 76.5 GPa, respectively. The combination of high λ_s, high B_s, low H_c, large ΔT_x, good ductility and high mechanical strength is promising a new type of ferromagnetic bulk amorphous alloy. © 1999 American Institute of Physics.