# Relation Between the Defect Interactions and the
## 4 Discussion  
For this investigation, the effects of annealing and strain rate on the microstructure and mechanical behavior of a Zr\({}_{52.5}\)Cu\({}_{17.9}\)Ni\({}_{14.6}\)Al\({}_{10}\)Ti\({}_{5}\) BMG were examined. The microstructure was examined using \begin{table}
\begin{tabular}{c c c} \hline
**Sample Condition** & **Strain Rate (s\({}^{-1}\))** & **A\({}_{\text{SE}}\)** \\ \hline As-cast & \(2\times 10^{-5}\) & 2.4 \\ \(2\times 10^{-4}\) & 4.2 \\ \hline
300 \({}^{\circ}\)C, 1 week & \(2\times 10^{-5}\) & 15.4 \\ \(2\times 10^{-4}\) & 28.5 \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of the A\({}_{\text{SE}}\) value for the as-cast and thermally annealed (300 \({}^{\circ}\)C, 1 week) Zr\({}_{52.5}\)Cu\({}_{17.9}\)Ni\({}_{14.6}\)Al\({}_{10}\)Ti\({}_{5}\) BMG, for strain rates of \(2\times 10^{-5}\) s\({}^{-1}\) and \(2\times 10^{-4}\) s\({}^{-1}\). Figure 4: A comparison of the sample entropy vs. the scale factor for the (**a**) as-cast and annealed (300 \({}^{\circ}\)C, 1 week) Zr\({}_{52.5}\)Cu\({}_{17.9}\)Ni\({}_{14.6}\)Al\({}_{10}\)Ti\({}_{5}\) BMG specimen that was compressed at a strain rate of \(2\times 10^{-5}\) s\({}^{-1}\), (**b**) as-cast and annealed (300 \({}^{\circ}\)C, 1 week) Zr\({}_{52.5}\)Cu\({}_{17.9}\)Ni\({}_{14.6}\)Al\({}_{10}\)Ti\({}_{5}\) BMG specimen that was compressed at a strain rate of \(2\times 10^{-4}\) s\({}^{-1}\), (**c**) as-cast samples compressed at strain rates of \(2\times 10^{-5}\) s\({}^{-1}\) and \(2\times 10^{-4}\) s\({}^{-1}\), and (**d**) the annealed sample (300 \({}^{\circ}\)C, 1 week) compressed at strain rates of \(2\times 10^{-5}\) s\({}^{-1}\) and \(2\times 10^{-4}\) s\({}^{-1}\). the bulk XRD, while nanoindentation and compression experiments were employed to examine the deformation behavior. Importantly, the XRD results (see Figure 1) suggest that the alloy did not crystallize during annealing at 300 \({}^{\circ}\)C for one week. This result is corroborated by a previous investigation, which found that the same alloy did not crystallize during annealing at 300 \({}^{\circ}\)C for up to two weeks [47]. As observed in Figure 2a, annealing the specimen at 300 \({}^{\circ}\)C for 1 week was found to significantly increase the nanoindentation hardness of the alloy. This increase in the hardness arises from the thermally-induced structural relaxation of the alloy. Moreover, the structural relaxation is a consequence of the thermal annihilation of the SZ defects in the alloy [47]. For example, [PERSON] et al. estimated that in the Zr\({}_{52.5}\)Cu\({}_{17.9}\)Ni\({}_{14.6}\)Al\({}_{10}\)Ti\({}_{5}\) BMG, annealing at 300 \({}^{\circ}\)C for 1 week (the same alloy and thermal conditions as the present study) reduced the density of these defects by almost two orders of magnitude [14]. These defects consist of loosely-packed regions and structural heterogeneities that can accommodate shear deformation under an applied load, relative to the glass matrix [15]. Moreover, the loss of SZ defects during structural relaxation can result in an increased difficulty of shear-band initiation. Consequently, their destruction would lead to an increased resistance to deformation that corresponds to an increase in the hardness. Similar to the hardness results, the nanoindentation Young's modulus (see Figure 2b) also significantly increased during annealing. The increase in the modulus is accompanied by a decrease in the interatomic spacing. It has been shown that an increase in the interatomic spacings, via structural rejuvenation, results in an increase in the number of liquid-like sites (or SZ defects) in the glass [50; 51]. Therefore, the converse should also hold true, i.e., a decrease in the interatomic distance caused by thermally-induced structural relaxation will result in fewer SZ defects. This hypothesis is corroborated by [PERSON] et al. [14], where it was reported that the structural relaxation led to a decrease in the SZ defect density of the Zr\({}_{52.5}\)Cu\({}_{17.9}\)Ni\({}_{14.6}\)Al\({}_{10}\)Ti\({}_{5}\) BMG.