Abstract
A series of Zr50.75Cu35.75Al8.5Ag5 bulk metallic glasses (BMGs) were prepared by controlling the cooling rate and over-heating temperature. The plastic deformation behavior of the BMGs was examined. The plasticity was enhanced when the BMG was prepared at a high cooling rate and low over-heating temperature. The plasticity of the Zr-based BMGs prepared under different casting conditions was discussed based on the amount of free volume. The structural heterogeneity of the BMGs prepared with different over-heating temperatures was examined using a high-resolution transmission electron microscope and mapped by using an energy dispersive x-ray spectroscope. The results showed that a low over-heating temperature could increase the degree of heterogeneity, but an extremely low over-heating temperature could lead to nanocrystallization. The difference in the heterogeneous structures caused the distinct plastic performance of the Zr50.75Cu35.75Al8.5Ag5 BMGs prepared with different over-heating temperatures.
Highlights
Bulk metallic glasses (BMGs) are usually prepared by quenching alloy melts in the amorphous state
For the bulk metallic glasses (BMGs) prepared with cooling rate (CR) of 250 and 40 K/s, the corresponding engineering plastic strains are 4.6% and 1.9%
For the BMGs prepared with the over-heating temperatures of 1303, 1453, and 1603 K, the engineering plastic strains are 4.4, 2.9, and 0, respectively
Summary
Bulk metallic glasses (BMGs) are usually prepared by quenching alloy melts in the amorphous state. The melt temperature and cooling rate (CR) play important roles in the formation of BMGs.. Any alloy melt can be frozen into an amorphous structure at the appropriate CR. The CR remarkably influences the microstructure of BMGs.. A high CR may loosen the atomic structure with increased free volume (FV).. The FV in the BMGs has a significant effect on the plasticity because the FV can play the role of the site for shear band (SB) branching and restrict the extension of the SB. As it was stated that even a small change in the FV can induce a significant effect on the deformation behavior of BMGs, reducing the FV will restrict the plasticity of these materials. Large amounts of FV around the atoms can amplify the internal atomic spacing and decrease the strength of the atomic bonding. As it was stated that even a small change in the FV can induce a significant effect on the deformation behavior of BMGs, reducing the FV will restrict the plasticity of these materials.
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