Variability of Poisson's Ratio and Enhanced Ductility in Amorphous Metal

Abstract Ductile bulk metallic glass of composition 53.0Zr–18.7Cu–12.0Ni–16.3Al (at%) is plastically deformed under uniaxial compression and observed in situ by synchrotron high‐energy X‐ray diffraction. The diffraction patterns reveal the induced atomic strain is orientation dependent. At the onset of plastic deformation, the atomic strain in the compression direction saturates to a close‐nearest‐neighbor distance while atoms relax in the transverse direction. The ever increasing transverse atomic strain expresses in an augmentation of the apparent Poisson's ratio up to ν = 0.5, which is consistent with volume conservation. Contradicting phenomena from linear mechanics, such as the non‐vanishing shear modulus at ν = 0.5 can be explained by the non‐affine character of the deformation, giving rise to characteristics of a localized martensitic phase transformation. The findings explain the often‐reported phenomena such as, the high Poisson's ratio values found in metallic glasses, the partially liquid character of the structure, the free volume increase and the Bauschinger effect.