Identification and Characterization of Potential Shear Transformation Zones in Metallic Glasses

The stability of local atomic configurations in a Ni-Zr metallic glass is studied by molecular dynamics. It is shown that individual atom displacements induce irreversible atomic rearrangements under different glass relaxation, temperature, and strain conditions. The number of regions with an unstable topology depends on the glass relaxation degree. Their time evolution is governed by thermal activation, the activation energy decreasing with elastic strain. It is also shown that unstable regions are located in correspondence of shear transformation zones operating under plastic deformation.

Figure 1

The distribution $p(\Delta r)$ of $\Delta r$ values for species involved in IRs ( gray bars) and others (hollow bars). The inset shows the distribution $p(k_{\min })$ of the minimum values $k_{\min }$ above which IRs take place. Data refer to $C\mathrm{\text{−}}\mathrm{I}(300;0;2)$.

Figure 2

(a) The number $N_{\mathrm{IR}}$ of IRs as a function of $\dot{Q}$. (b) The Neperian logarithm $\ln {\dot{N}}_{\mathrm{IR}}$ of the rate ${\dot{N}}_{\mathrm{IR}}$ of IR thermal activation as a function of $T^{-1}$. Best-fitted lines are also shown. Data refer to $C\mathrm{\text{−}}\mathrm{I}(T;0;2)$ systems.

Figure 3

The average $⟨k_{\min }⟩$ values and the number $N_{\mathrm{IR}}$ of IRs as a function of strain ${\epsilon }_x$. Data refer to $C\mathrm{\text{−}}\mathrm{I}(300;0;2)$ (□), $C-I(300;0;2)$ (○), $C\mathrm{\text{−}}\mathrm{I}(300;0;2)$ (▵), and $C\mathrm{\text{−}}\mathrm{I}(300;0;2)$ (▿) glasses. Quadratic curves are best-fitted on $C\mathrm{\text{−}}\mathrm{I}(300;0;2)$ data.

Figure 4

(a) The Neperian logarithm $\ln {\dot{N}}_{\mathrm{IR}}$ of the IR rate of change ${\dot{N}}_{\mathrm{IR}}$ as a function of $T^{-1}$ for $C\mathrm{\text{−}}\mathrm{IV}(300;0.06;2)$. The best-fitted line is also shown. (b) The IR activation energy $E_{a,\epsilon }$ as a function of strain ${\epsilon }_x$. Data refer to $C\mathrm{\text{−}}\mathrm{IV}(300;{\epsilon }_x;2)$ (□), $C\mathrm{\text{−}}\mathrm{IV}(500;{\epsilon }_x;2)$ (○), $C\mathrm{\text{−}}\mathrm{IV}(700;{\epsilon }_x;2)$ (▵), and $C\mathrm{\text{−}}\mathrm{IV}(900;{\epsilon }_x;2)$ (▿). The dotted line has been best-fitted on $C\mathrm{\text{−}}\mathrm{IV}(300;{\epsilon }_x;2)$ (□) values. The dotted curve is a guide to the eyes.

Figure 5

A STZ before (left) and after (right) operation. Data refer to $C\mathrm{\text{−}}\mathrm{IV}(500;0.06;2)$. Dark and light gray indicate, respectively, Zr and Ni atoms.