Bulk metallic glasses (BMGs) generally fail in a brittle manner under uniaxial, quasistatic loading at room temperature. The lack of plastic strain is a consequence of shear softening, a phenomenon that originates from shear-induced dilation that causes plastic strain to be highly localized in shear bands. So far, significant tensile ductility has been reported only for microscopic samples of around 100 nm (ref. 4) as well as for high strain rates, and so far no mechanisms are known, which could lead to work hardening and ductility in quasistatic tension in macroscopic BMG samples. In the present work we developed CuZr-based BMGs, which polymorphically precipitate nanocrystals during tensile deformation and subsequently these nanocrystals undergo twinning. The formation of such structural heterogeneities hampers shear band generation and results in macroscopically detectable plastic strain and work hardening. The precipitation of nanocrystals and their subsequent twinning can be understood in terms of a deformation-induced softening of the instantaneous shear modulus. This unique deformation mechanism is believed to be not just limited to CuZr-based BMGs but also to promote ductility in other BMGs.

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The structural behaviour of Cu 50 Zr 50 and Cu 65 Zr 35 metallic glasses under uniaxial tensile stress was investigated in situ by high-energy X-ray synchrotron diffraction. The components of the elastic strain tensor were determined from both the change of positions of first maximum of the structure factor in reciprocal space as well as from the maxima of the atomic pair correlation function in real space. The atomic scale strain agrees with the macroscopic strain values. The topological and chemical short-range order of the Cu-Zr glasses changes upon loading. The number density of Cu-Zr and Zr-Zr nearest neighbour atomic pair becomes oriented along the loading direction whereas the partial nearest neighbour distances are only weakly influenced.

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Ti-based bulk metallic glasses (BMGs) with large compressive plasticity were developed in the Ti-rich part of Vitreloy series BMGs (Ti 65-x Zr x Cu 9 Ni 8 Be 18 alloys with x = 0, 5, 10, 15, and 20). The current materials exhibit high fracture strength reaching~2.3 GPa and plastic strains up tõ 8.3 pct after partial substitution of Zr by Ti. The plasticity of the investigated alloys strongly depends on the Zr content, which affects the elastic constants, such as Poisson's ratio and shear modulus. This, in turn, has an impact on the shear transformation zone (STZ) volume and, hence, on the shear banding of the glasses.

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The structural evolution of the Ti40Zr10Cu34Pd14Sn2 bulk metallic glass (BMG) upon was investigated by means of in situ high-energy x-ray diffraction. The position, width, and intensity of the first peak in diffraction patterns are fitted through Voigt function below 800 K. All the peak position, width, and intensity values show a nearly linear increase with the increasing temperature to the onset temperature of structural relaxation, Tr = 510 K. However, these values start to deviate from the linear behavior between Tr and Tg (the glass transition temperature). The changes in free volume and the coefficient of volume thermal expansion prove that the aforementioned phenomenon is closely related to the structural relaxation releasing excess free volume arrested during rapid quenching of the BMG. Above 800 K, three crystallization events are detected and the first exothermic event is due to the formation of metastable nanocrystals.