NMR Signature of Evolution of Ductile-to-Brittle Transition in Bulk Metallic Glasses

Abstract

The mechanical properties of monolithic metallic glasses depend on the structures at atomic or subnanometer scales, while a clear correlation between mechanical behavior and structures has not been well established in such amorphous materials. In this work, we find a clear correlation of (27)Al NMR isotropic shifts with a microalloying induced ductile-to-brittle transition at ambient temperature in bulk metallic glasses, which indicates that the (27)Al NMR isotropic shift can be regarded as a structural signature to characterize plasticity for this metallic glass system. The study provides a compelling approach for investigating and understanding the mechanical properties of metallic glasses from the point of view of electronic structure.

Chemical influence on β-relaxations and the formation of molecule-like metallic glasses

“…For the considerations of glass-forming ability, Ni and Cu are even sometimes regarded as same 33,34 . Distinctively, we note the mechanical behaviours (especially, the ductility and toughness) of MGs are sensitive to chemical effects 35,36 , in agreement with the notion that mechanical properties and b-relaxations are correlated 21,22 .…”

Mechanical properties and structural features of novel Fe-based bulk metallic glasses with unprecedented plasticity

“…The p-d hybrid bonds are strong covalent and thus should resist shear while the s -like bonds are relatively weak and thus more easily accommodate shear. Hence, BMGs are expected to exhibit ductile nature if the electronic configuration becomes mostly s -like and has more likely uniform valence charge density, because the bonding in this case will be more non-directional27. In other words, during the shear moving of atoms, the p-d hybrid bonds are more prone to broke due to the obvious change of atomic orbital overlap, while non-directional s character bonds with good mobility can absorb more energy at crack tip as atoms can yield long distance, dissipate larger amount of fracture energy and exhibit more plasticity.…”

“…Theoretically, several structural models such as free volume22, shear transformation zone23 and efficient cluster packing theories2425 have been proposed to explain the plastic flow and fracture; whereas these models in terms of packing based on atomic size and configuration have failed to interpret the nature of atomic bonding in BMGs, which is indispensable for a better understanding of their mechanical behavior involved in brittle to ductile transition. Recently, theoretical calculations have illuminated that the hybrid character of interatomic bonds of multicompositions may contribute to the intrinsic plasticity versus brittleness of BMGs by controlling the bond mobility172627. In contrast, the order parameter obtained from experiments to characterize the nature of bond mobility and its evolution on alloying in BMGs is still lacking.…”

The fracture of bulk metallic glasses

“…The DBT induced by microalloying may also relates with the change of electronic structure [13,225]. Yuan et al [225] investigated the evolution of bonding states for composition-induced DBT in a ZrCuNiAlSn x BMG by employing 27 Al NMR spectroscopy.…”

“…Yuan et al [225] investigated the evolution of bonding states for composition-induced DBT in a ZrCuNiAlSn x BMG by employing 27 Al NMR spectroscopy. As shown in Fig.…”