Superplastic deformation behaviour of Zr 41.25 Ti 13.75 Ni 10 Cu 12.5 Be 22.5 bulk metallic glass in the supercooled liquid region

Abstract

This paper presents the tensile deformation behavior of Zr 41.25Ti13.75Ni10Cu12.5Be 22.5 (at%) bulk metallic glass in the supercooled liquid region. Isothermal tensile tests were carried out at four characteristic temperatures of 616, 636, 656 and 676 K which are in the range from glass transition temperature (∼616 K) to onset crystallization temperature (∼690 K). The results show that the superplastic flow behaviors of the material (flow stress and elongation to fracture) vary, depending strongly on the test temperatures and initial strain-rate. At a given temperature, the elongation first increases and then decreases with the initial strain-rates increasing, and the maximum elongation was found to be as high as 1625% at the temperature of 656 K with the strain-rate of 7.6×10-3 s-1DSC analysis shows the crystallized volume fraction in the deformed section is always higher than that of the undeformed section in the specimens. The maximum elongation always corresponds to the maximum crystallized volume fraction. Nanocrystals homogeneously embedded in the amorphous matrix of the deformed specimens were observed by transmission electron microscope. It is conjectured that the nanocrystallization was induced by the flow stress and environmental temperature.