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

We have investigated the deformation behavior and the influence of deformation on the soft-magnetic properties for a ferromagnetic Fe72Hf8Nb2B18 (at.%) metallic glass that has a wide supercooled liquid region of 76 K before crystallization and good soft-magnetic properties. The metallic glass was found to exhibit superplasticity at the supercooled liquid state. The maximum elongation to failure was 240% that was obtained at 873 K (Tg+17 K) and at 1.7×10−3 s−1 under a flow stress of about 100 MPa. In this condition, 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 expressed well by a stretched exponential function σflow=3Cε̇ exp(H/RT)[1−exp(A/{Bε̇ exp(H∗/RT)}0.85)].