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 ${\mathrm{Fe}}_{\text{80−x−y}}{\mathrm{Co}}_x{\mathrm{Ln}}_y{\mathrm{B}}_{\mathrm{20}}$ $(\mathrm{Ln=Nd},$ Sm, Tb, or Dy) amorphous alloys. The supercooled liquid region ${\mathrm{(\Delta T}}_x)$ shows the largest value of 41 K for the ${\mathrm{Fe}}_{\mathrm{47}}{\mathrm{Co}}_{\mathrm{30}}{\mathrm{Sm}}_{\mathrm{3}}{\mathrm{B}}_{\mathrm{20}}$ 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 ${\mathrm{(B}}_s)$ of 0.84–1.66 T and coercivity ${\mathrm{(H}}_c)$ of 5.0–36 A/m. A high magnetostriction ${\mathrm{(\lambda }}_s)$ exceeding ${\text{40×10}}^{\text{−6}}$ was also observed in the composition range of 0–10 at % Co and 1.5–3 at % Ln $(\mathrm{Ln=Sm},$ Tb, or Dy). The highest ${\lambda }_s$ reaches ${\text{58×10}}^{\text{−6}}$ for ${\mathrm{Fe}}_{\mathrm{68.5}}{\mathrm{Co}}_{\mathrm{10}}{\mathrm{Ln}}_{\mathrm{1.5}}{\mathrm{B}}_{\mathrm{20}}$ $(\mathrm{Ln=Sm}$ or Tb), which is higher than the highest value ${\text{(44×10}}^{\text{−6}})$ for previously reported amorphous alloys. All the ${\mathrm{Fe}}_{\mathrm{68.5}}{\mathrm{Co}}_{\mathrm{10}}{\mathrm{Ln}}_{\mathrm{1.5}}{\mathrm{B}}_{\mathrm{20}}$ amorphous alloys have good bending ductility. The tensile strength, Vickers hardness and Young’s modulus of the ${\mathrm{Fe}}_{\mathrm{68.5}}{\mathrm{Co}}_{\mathrm{10}}{\mathrm{Sm}}_{\mathrm{1.5}}{\mathrm{B}}_{\mathrm{20}}$ alloy are 3220 MPa, 990 and 76.5 GPa, respectively. The combination of high ${\lambda }_s,$ high $B_s,$ low $H_c,$ large ${\mathrm{\Delta T}}_x,$ good ductility and high mechanical strength is promising a new type of ferromagnetic bulk amorphous alloy.