Towards more uniform deformation in metallic glasses: The role of Poisson's ratio

Abstract

a b s t r a c tWe develop a quantitative analysis of how the plastic deformation in a metallic glass is more uniform if its Poisson ratio n is higher. The plasticity of metallic glasses under ambient conditions is mediated by shear localized in thin bands, and can be characterized by experiments on the bending of thin plates. We extend the analysis by Conner et al. (Conner et al., J. Appl. Phys. 94 (2003), 904-911) of bands in bent plates to include the micromechanics of individual shear bands. Expressions are derived for the shearband spacing and the offset on each band. Both these quantities are predicted to decrease as n is increased. The predictions are tested against measurements on metallic glasses with a wide range of n.Good agreement is found, supporting the new model for the shear-band spacing, and pointing the way towards more diffuse deformation, and consequently improved plasticity and toughness, of metallic glasses as n increases toward the limiting value of 0.5. Crown

Spiral fracture in metallic glasses and its correlation with failure criterion

“…We hence use the term ''failure" instead of ''yielding" to describe the critical combinations of shear and normal stress which trigger fracture in Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 . It is noted that there could be possibilities when shear banding does not lead to catastrophic failure, for example in bending tests [37] and in indentation experiments [21][22][23][24]. In those states of stress, ''yielding" apparently differs from ''failure".…”

Strength softening at shear bands in metallic glasses

“…The bending of thin plates is particularly useful and widely used for studies of SBs since the propagation of SBs ceases as they approach the neutral plane, and early catastrophic failure is avoided, permitting substantial deformability when the samples are sufficiently thin [28][29][30][31][32][33]. Here by utilizing the SBs formed after bending but before the rupture of the material, we continue to perform in situ tensile tests with the bent samples, and then derive the strength loss at SBs in MGs after obtaining the strength of samples with pre-existing SBs.…”

“…In order to obtain the strength r sb in SBs, we need to determine the SB length at a given bending ratio. With the approximation of plane strain bending (which is the case here since the sample width is at least four times larger than the thickness H, as seen in Figure 1a, the characteristic length of a SB (projected length along the plate thickness) is obtained by calculating the distance from the neutral plane at which the stress reaches the critical value r c for SB initiation [28][29][30]33], which is given as…”

Review on the Research and Development of Ti-Based Bulk Metallic Glasses

“…There is also a correlation between the elastic properties (e.g., Young's modulus E and Poisson's ratio ν) and room temperature plasticity of BMGs. It was reported that BMGs with a higher Poisson's ratio (e.g., >0.32) may possess larger plasticity [149,150]. In this sense, Ti-based BMGs can be classified as "ductile" because of the relatively high Poisson's ratio.…”