Flow Stress and Elongation of Superplastic Deformation in La₅₅Al₂₅Ni₂₀ Metallic Glass

<jats:title>Abstract</jats:title><jats:p>We have investigated the flow stress and elongation of superplastic deformation in a La<jats:sub>55</jats:sub>Al<jats:sub>25</jats:sub>Ni<jats:sub>20</jats:sub> (at%) metallic glass that has a wide supercooled liquid region of 72 K before crystallization. The superplasticity that appeared in the supercooled liquid region was generated by the Newtonian viscous flow that exhibits the <jats:italic>m</jats:italic> value of unity. The elongation to failure was restricted by the transition of the Newtonian flow to non-Newtonian one and the crystallization during deformation. We succeeded in establishing the constitutive formulation of the flow stress in the supercooled liquid region. Its formulation was expressed very well by a stretched exponential function σ<jats:sub>flow</jats:sub>=<jats:italic>D</jats:italic>ε exp(<jats:italic>H</jats:italic>*/<jats:italic>RT</jats:italic>) [1-exp(<jats:italic>E</jats:italic>/{ε exp(<jats:italic>H</jats:italic>**/<jats:italic>RT</jats:italic>)}<jats:sup>0.82</jats:sup>)]. Formulations describing the elongation to failure in constant-strain-rate and constant-crosshead velocity tests were, moreover, established. It was found from the simulation that the maximum elongation in the constant-strain-rate test reached more than 10<jats:sup>6</jats:sup>% which was two orders of magnitude larger than that in the constant-crosshead-velocity test.</jats:p>