Superplastic deformation behavior of Zr_(41.25)Ti_(13.75)Ni_(10)Cu_(12.5)Be_(22.5) bulk metallic glass in the supercooled liquid region

摘要

This paper presents the tensile deformation behavior of Zr_(41.25)Ti_(13.75)Ni_(10)Cu_(12.5)Be_(22.5) (at percent) bulk metallic glass in the supercooled liquid region. Isothermal tensile tests were earned out at four characteristic temperatures of 616, 636, 656 and 676 K which are in the range from glass transition temperature (approx 616 K) to onset crystallization temperature (approx 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-rates. At a given temperature, the elongation first increases and then decreases with the initial strain-rate increasing, and the maximum elongation was found to be as high as 1625 percent at the temperature of 656 K with the strain-rate of 7.6 X 10~(-3) s~(-1). DSC 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.