Dynamics Of Metallic Glass Research Articles

Deformation-induced change in the structure of metallic glasses during multistep indentation

The perplexing controversy of whether deformation-induced hardening/softening is intrinsic or extrinsic remains an outstanding fundamental problem in the low-temperature rheology and dynamics of metallic glasses. In this Brief Report, by manipulating nanoscale plastic deformation in a multistep instrumented indentation process, we in situ characterize and definitively elucidate the deformation-driven structural changes in metallic glasses via their strengthening or softening effect on consecutive mechanical behavior.

Effect of local structures and atomic packing on glass forming ability in CuxZr100−x metallic glasses

Molecular dynamics simulations are performed for CuZr metallic alloys to study the structural and dynamical features for glass forming ability (GFA). Our analysis shows that in CuZr metallic system, although ⟨0,0,12,0⟩ icosahedral clusters are important, some Zr-centered clusters such as ⟨0,1,10,4⟩ and ⟨0,1,10,5⟩ play a key role in slowing down the dynamics. It is found that these Zr-centered clusters are intrinsically slow and fundamentally determine the stability and slow dynamics. Due to the strong spatial correlation between ⟨0,0,12,0⟩ and Zr-centered clusters, their relative population influences the dense packing and dynamics in metallic glasses, and further the GFA.

Elasticity in metallic glasses

The unique nature of elasticity in metallic glasses will be discussed with particular focus on the intrinsic anelasticity. Although the bulk modulus of a metallic glass is comparable in magnitude to that of the corresponding crystalline solid, the shear modulus is always lower by 20% to 30%. This is because shear deformation of a metallic glass produces not only the geometrical deformation but also local topological changes of atomic bonding. Even in the glassy state there is some local residue of liquidity due to local structural frustrations, and this makes the shear deformation in metallic glasses intrinsically anelastic. On this point glasses are fundamentally different from crystals. This intrinsic anelasticity results in anomalous dependence of shear modulus and anelastic loss on frequency and temperature, including the low-temperature two-level state behavior. Based upon computer simulation, neutron scattering experiment, and theory, the intrinsic nature of anelasticity will be shown to be a part of the big picture of the structure and dynamics of metallic glasses.

Comment on “High-Frequency Dynamics in Metallic Glasses”

A Comment on the Letter by T. Scopigno et al., [Phys. Rev. Lett. 96, 135501 (2006)]. The authors of the Letter offer a Reply.

Atomic Dynamics in Metallic Liquids and Glasses

How atoms move in metallic glasses and liquids is an important question in discussing atomic transport, glass formation, structural relaxation and other properties of metallic glasses. While the concept of free-volume has long been used in describing atomic transport, computer simulations and isotope measurements have shown that atomic transport occurs by a much more collective process than assumed in the free-volume theory. We introduce a new approach to describe the atomic dynamics in metallic glasses, in terms of local energy landscapes related to fluctuations in the topology of atomic connectivity. This approach may form the basis for a new paradigm for discussing the structure-properties relationship in metallic glasses.

High-Frequency Dynamics in Metallic Glasses

Using inelastic x-ray scattering we studied the collective dynamics of the glassy alloy Ni33Zr67 in the first pseudo-Brillouin-zone, an energy-momentum region still unexplored in metallic glasses. We determine key properties such as the momentum transfer dependence of the sound velocity and of the acoustic damping, discussing the results in the general context of recently proposed pictures for acoustic dynamics in glasses. Specifically, we demonstrate the existence in this strong glass of well defined (in the Ioffe-Regel sense) acoustic-like excitations well above the boson peak energy.

Slow dynamics of metallic glass measured at room temperature with a fiber optic interferometer

Transversely annealed strips of metallic glass have been probed using a fiber interferometer. This technique can measure strain variations down to 10/sup -13///spl radic/Hz. We report measurements of low-frequency 1/f type noise stemming from localized magnetic relaxation in the amorphous material.