Flow stress and elongation of superplastic deformation in La55Al25Ni20 metallic glass

The authors have investigated the flow stress and elongation of superplastic deformation in a La55Al25Ni20 (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 m 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. They 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 σflow = D. ε exp (H*/RT) [1-exp(E/{ε exp (H**/RT)}0.82)]. 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 reached more than 106% which was two orders of magnitude larger than that in the constant-crosshead-velocity test