# Understanding the Fracture Behaviors of Metallic Glasses--An Overview
## 2 Fracture Behaviors of MGs
### Impact Toughness of MGs  
The impact toughness reflects the damage resistance of a material under impact loading. At present, the impact toughness data of MGs are still few. As the size requirement of the standard test (\(10\times 10\times 55\) mm) can hardly be reached by most MGs. Only a small number of MGs can achieve a critical size over 10 mm [53; 54; 55; 56; 57; 58]. Many impact toughness data are measured through nonstandard  
Figure 4: Appearance of a Pd77.5 Cu6 Si16.5 MG sample with a size of \(2.2\times 3.8\times 25\) mm\({}^{3}\) after 3-point bending. (**a–c**) Side surface appearance. (**d–f**) Fracture surface appearance. Figure 5: Appearance of a Vitreloy-1 MG rod with a size of \(\varphi\)2 after 3-point bending. (**a,b**) Side surface appearance. (**c–e**) Fracture surface appearance. (**f**) Loading curve. small samples. Table 1 shows a collection of reported impact toughness data of several MGs. Although there is doubt about the reliability of the data measured in nonstandard samples, the highest measured impact toughness in MGs is not higher than 160 kJ/m\({}^{2}\). This value is relatively smaller than that of AISI-1018 steel [59]. Figure 6 shows a typical impact fracture morphology of a (Ti4 IZr25 Be28 Fe6)91 Cu9 MG, which is very similar to that of mode I fracture. The fractograph starts with a smooth region and flat zone (Figure 6b), which are formed during shear band sliding and delamination. The other positions of the fractograph are rough, with many ridge patterns. Plentiful vein patterns and viscous features can be observed on the enlarged images of the fractograph (Figure 5d-f). The fracture direction changes obviously near the end of the sample (Figure 6c), which results from the changed stress condition at this position and the existence of shear bands generated by the impact hammer. The loading rate of impact toughness test is much faster than that of conventional static tests, and is also much faster than that of shear band sliding. Generally, the shear band sliding speed in MGs is at the magnitude of 1 mm/s or less [68; 69]. The speed of pendulum hammer in the impact toughness \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Composition** & \begin{tabular}{c} **Sample Size** \\ **(mm \(\times\) mm \(\times\) mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Deepness and Shape** \\ **of Notch** \\ \end{tabular} &
\begin{tabular}{c} **Impact Energy** \\ **(k/m\({}^{2}\))** \\ \end{tabular} \\ \hline \((\text{Ti}_{36.1}\text{Zr}_{33.2}\text{Ni}_{5.8}\text{Be}_{24.9}\text{)}_{95}\text{ Cu}_{5}\) & \(10\times 10\times 55\) & U-shape & 50 [60] \\ \(\text{Zr}_{55}\text{Al}_{10}\text{Cu}_{30}\text{Ni}_{5}\) & \(2.6\times 10\times 55\) & U-shape & 63 [61] \\ \(\text{Zr}_{50}\text{Cu}_{40}\text{Al}_{10}\) & \(5\times 10\times 55\) & U-shape & 100 [62] \\ \(\text{Zr}_{41.2}\text{Ti}_{13.8}\text{Cu}_{12.5}\text{Ni}_{10}\text{Be}_{22.5}\) & \(3\times 3\times 30\) & 1 mm V-shape & 80 \(\sim\) 160 [63] \\ \(\text{Zr}_{41.2}\text{Ti}_{13.8}\text{Cu}_{12.5}\text{Ni}_{10}\text{Be}_{22.5}\) & \(3\times 6\times 30\) & 3 mm V-shape & 133 [64] \\ \(\text{La}_{55}\text{Al}_{25}\text{Cu}_{10}\text{Ni}_{5}\text{Co}_{5}\) & \(2.6\times 5\times 22\) & 1 mm & 77 [65] \\ \(\text{Zr}_{41.2}\text{Ti}_{13.8}\text{Cu}_{12.5}\text{Ni}_{10}\text{Be}_{22.5}\) & \(3\times 6\times 30\) & 3 mm & 90 \(\sim\) 133 [66] \\ \(\text{Pd}_{40}\text{Cu}_{30}\text{Ni}_{10}\text{Pa}_{20}\) & \(2.5\times 10\times 55\) & 2 mm U-shape & 70 [67] \\ \(\text{Ti}_{28.2}\text{Zr}_{30.2}\text{Be}_{26}\text{Se}_{30}\text{Cu}_{95}\text{ Cu}_{9}\) & \(10\times 10\times 55\) & 2 mm U-shape & 50 [60] \\ \((\text{Ti}_{44}\text{Zr}_{25}\text{Be}_{28}\text{Fe}_{6})_{91}\text{Cu}_{9}\) & \(10\times 10\times 55\) & 2 mm U-shape & 60 \\ AISI-1018 steel & \(10\times 10\times 55\) & 2 mm V-shape & \(\sim\)500 [59] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Impact toughness data of different metallic glasses. Figure 6: Fractograph morphology of a (Ti4 IZr25 Be28 Fe6)91 Cu9 MG after impact toughness test.