Superplasticity in Fe-based metallic glass with wide supercooled liquid region

We have investigated the deformation behavior and the influence of deformat ion on the soft-magnetic properties for a ferromagnetic Fe72Hf8Nb2B18 (at.% ) metallic glass that has a wide supercooled liquid region of 76 K before c rystallization and good soft-magnetic properties. The metallic glass was fo und to exhibit superplasticity at the supercooled liquid state. The maximum elongation to failure was 240% that was obtained at 873 K (T-g + 17 K) and at 1.7 x 10(-3) s(-1) under a flow stress of about 100 MPa. In this condit ion, crystallization occurred at elongation above 100%, resulting from the lack of thermal stability. The metallic glass was, however, deformed up to an elongation of 100% with retaining the good soft-magnetic properties and glassy phase. We succeeded in establishing the constitutive formulation of the flow stress in the supercooled liquid region. Its formulation was expre ssed well by a stretched exponential function sigma (flow) = 3C epsilon exp (H/RT)[1 - exp(A/{B epsilon exp(H*/RT)}(0.85))]. (C) 2001 Elsevier Science B.V. All rights reserved.