Superplastic deformation of Zr₅₅Cu₃₀Al₁₀Ni₅bulk metallic glass in the supercooled liquid region

In this paper, the superplastic deformation of Zr55Cu30Al10Ni5bulk metallic glass (BMG) was studied at a temperature of 430 °C (in the supercooled liquid region) under uniaxial tension over a wide range of strain rates from 8 × 10-4to 4 × 10-2s-1. It has been found that the superplastic behavior of the BMG is strongly dependent on the strain rate. The BMG exhibited Newtonian behavior at the low strain rate regime, but became non-Newtonian at the higher strain rate regime. A maximum elongation of 550% was achieved at a strain rate of 2.5 × 10-3s-1. On the other hand, structural investigations revealed that plastic deformation could promote the re-ordering and nanocrystallization of the amorphous structure of the BMG. It was also found that a band structure with strongly orientated nanocrystals inside was formed in case of using the high strain rate. The non-Newtonian behavior at the high strain rate regime is discussed in terms of the changes of stress-induced free volume and the concurrent nanocrystallization induced by deformation.