Extraordinary Plasticity of Ductile Bulk Metallic Glasses

Shear bands generally initiate strain softening and result in low ductility of metallic glasses. In this Letter, we report high-resolution electron microscope observations of shear bands in a ductile metallic glass. Strain softening caused by localized shearing was found to be effectively prevented by nanocrystallization that is in situ produced by plastic flow within the shear bands, leading to large plasticity and strain hardening. These atomic-scale observations not only well explain the extraordinary plasticity that was recently observed in some bulk metallic glasses, but also reveal a novel deformation mechanism that can effectively improve the ductility of monolithic metallic glasses.

Figure 1

(a). HREM image and FFT pattern of the as-spun ${\mathrm{Zr}}_{50}{\mathrm{Cu}}_{50}$ BMG. (b). Fourier-filtered HREM image that was reconstructed by a series of images produced with a different aperture sizes.

Figure 2

TEM observations of shear bands in the deformed ${\mathrm{Zr}}_{50}{\mathrm{Cu}}_{50}$ BMG. (a) Bright-field TEM image of a narrow band with lighter contrast across the thin region of the TEM specimen. (b) Low-magnification HREM image of a shear band with precipitate nanoparticles. (c) HREM image of the shear band, taken from the region S in Fig. 2b. Slightly coarser maze clusters within the shear band can be seen. (d) Fourier-filtered HREM image showing that a shear band gradually becomes wider as approaching a nanoparticle.

Figure 3

Crystal defects in the nanoparticles shown in Fig. 2b. (a). Heavily distorted crystal lattices with dislocations and twins. These crystal defects associated with the plastic deformation were highlighted by the Fourier-filtered images in (b) and (c). (b) Two edge dislocations with Burgers vectors of $⟨1\overline{1}0⟩$ and $⟨001⟩$, respectively; and (c) deformation twins, stacking faults, and partial dislocations.