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-y)Co(x)Ln(y)B(20) (Ln=Nd, Sm, Tb, or Dy) amorphous alloys. The supercooled liquid region (Delta T-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 (lambda(s)) exceeding 40x10(-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 lambda(s) reaches 58x10(-6) for Fe(68.5)Co(10)Ln(1.5)B(20) (Ln=Sm or Tb), which is higher than the highest value (44x10(-6)) for previously reported amorphous alloys. All the Fe(68.5)Co(10)Ln(1.5)B(20) amorphous alloys have good bending ductility. The tensile strength, Vickers hardness and Young's modulus of the Fe68.5Co10Sm1.5B20 alloy are 3220 MPa, 990 and 76.5 GPa, respectively. The combination of high lambda(s), high B-s, low H-c, large Delta T-x, good ductility and high mechanical strength is promising a new type of ferromagnetic bulk amorphous alloy. (C) 1999 American Institute of Physics. [S0021-8979(99)21008-0].