Tensile Plasticity in Metallic Glasses with Pronounced $\beta$ Relaxations

Metallic glasses are commonly brittle, as they generally fail catastrophically under uniaxial tension. Here we show pronounced macroscopic tensile plasticity achieved in a La-based metallic glass which possesses strong $\beta$ relaxations and nanoscale heterogeneous structures. We demonstrate that the $\beta$ relaxation is closely correlated with the activation of the structural units of plastic deformations and global plasticity, and the transition from brittle to ductile in tension and the activation of the $\beta$ relaxations follow a similar time-temperature scaling relationship. The results have implications for understanding the mechanisms of plastic deformation and structural origin of $\beta$ relaxations as well as for solving the brittleness in metallic glasses.

Figure 1

The engineering stress-strain curves (in tension) tested at strain rates (a) $1.6\times {10}^{-6}$, (b) $1\times {10}^{-5}$, (c) $1\times {10}^{-4}$, and (d) $1\times {10}^{-3}{\mathrm{s}}^{-1}$. For clarity, only three representative stress-strain curves corresponding to three different testing temperatures are shown in each figure.

Figure 2

(a) The deformation mode map summarizing the tension tests at different temperature and strain rates; the filled squares denote the brittle fracture while filled circles are for the ductile fracture, and the DBT is represented by half-filled squares. (b) The temperature and strain rate dependence of the temperature of DBT and fitted with the Arrhenius relation. (c) The photograph of the La-MG before and after tension with stain 30% (at 353 K and $1\times {10}^{-5}{\mathrm{s}}^{-1}$). (d) The scanning electron microscope image of a ductile fracture surface of the La-MG (at 333 K and $1\times {10}^{-5}{\mathrm{s}}^{-1}$ and total strain 6%), and the arrow indicates the shear bands.

Figure 3

(a) Comparison of the behavior of $\beta$ relaxations between the La-based MG with ten other typical MGs. For comparison, the temperature is scaled by $T_g$ and the loss modulus $E^{\prime \prime }$ (1 Hz) is normalized by a corresponding maximum (at $T_g$). (b) Temperature-dependent $E^{\prime \prime }$ of the La-MG showing distinct $\beta$ relaxations peaks; the frequencies used are 0.5, 1, 2, 4, 8, and 16 Hz from left to right, respectively. The inset shows the frequency dependence of the peak and end-set temperature of the $\beta$ relaxations and fitted with Arrhenius relations.

Figure 4

The Arrhenius plot of temperature and effective frequencies dependent on DBT and the end set of the $\beta$ relaxation of the La-based MG.

Figure 5

(a) A scanning TEM image of the as-cast La-MG. (b) A high-resolution TEM micrograph of the as-cast La-MG; the inset shows the selected-area electron diffraction.