Plastic Deformation of Pressured Metallic Glass

Correlation between the topologically close-packed structure and the deformation behavior of metallic Cu64.5Zr35.5

The topologically close-packed (TCP) structural characteristics in a model metallic glass (MG) of Cu_64.5Zr_35.5 have been investigated by molecular dynamics simulations. A group of structural indicators based on the largest standard cluster (LaSC) have been correlated with the non-affine displacement (D²) of atoms, so as to reveal the hidden correlation between local structures and deformation behavior of Cu_64.5Zr_35.5 during compression. It was found that the 15 types of Top-10 LaSCs are all TCP-like ones, among which the most numerous icosahedron (Z12 and 1-Z12) decreases in population sharply and moderately during respectively the elastic and yield region of compression; while in the fluid-flow region, the number of all Top-10 LaSCs tends to be almost constant. Low-D² atoms prefer to link with each other; while medium-D² atoms act as transition structures between backbone areas and deformation areas. Most interestingly, the deformation response of TCP-like atoms is not only determined by its nearest neighbor characteristics, but also depends on the linkage with other atoms. In addition, icosahedral atoms with a higher degree of medium range five-fold symmetry (MRFFS) are more resistant to the stress-induced deformation. Therefore, the TCP characteristics, including its nearest neighbor feature and the inter-connection between TCP LaSCs, are closely related with the deformation behavior of atoms, especially the MRFFS (up to 5 layers) of icosahedral atoms. These findings shed new light on the understanding of the relationship between microstructure and deformation response of MGs, which will promote the development of deformation theory of MGs.

Molecular Dynamics Simulation of Structural Signals of Shear-Band Formation in Zr46Cu46Al₈ Metallic Glasses

The evolution from initiation to formation of a shear band in Zr46Cu46Al₈ metallic glasses is presented via molecular dynamics simulation. The increase in number and the decrease in average size of clusters with the quasi-nearest atoms being 0 correspond to the shear-band evolution from initiation to formation. When the shear band is completely formed, the distribution of the bond orientational order q₆ reaches a minimum. The maximum of the number of the polyhedral loss of Cu-centered <0, 0, 12, 0> and the minimum of the number of the polyhedral loss of Zr-centered <0, 2, 8, 5> correspond to the shear-band formation. These findings provide a strong foundation for characterizing the evolution from initiation to formation of shear bands.

Related Structure Characters and Stability of Structural Defects in a Metallic Glass

Structural defects were investigated by a recently proposed structural parameter, quasi-nearest atom (QNA), in a modeled Zr₅₀Cu₅₀ metallic glass through molecular dynamics simulations. More QNAs around an atom usually means that more defects are located near the atom. Structural analysis reveals that the spatial distribution of the numbers of QNAs displays to be clearly heterogeneous. Furthermore, QNA is closely correlated with cluster connections, especially four-atom cluster connections. Atoms with larger coordination numbers usually have less QNAs. When two atoms have the same coordination number, the atom with larger five-fold symmetry has less QNAs. The number of QNAs around an atom changes rather frequently and the change of QNAs might be correlated with the fast relaxation metallic glasses.