Characterization of Nanoscale Mechanical Heterogeneity in a Metallic Glass by Dynamic Force Microscopy

Liu, Y. H.; Wang, D.; Nakajima, Ken; Zhang, W.; Hirata, Akihiko; Nishi, Toshio; Inoue, Akihisa; Chen, M. W.

doi:10.1103/physrevlett.106.125504

Cited by 372 publications

(232 citation statements)

References 34 publications

(73 reference statements)

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“…S3 (a 3D view from outside the MD box is in Fig. S4), in terms of property (soft spots) and corresponding structure (GUMs), may also help explain the origin of the heterogeneity in local elastic modulus and local viscoelasticity recently mapped out in experiments (26)(27)(28).…”

Section: Significancementioning

confidence: 93%

Soft spots and their structural signature in a metallic glass

Ding

Patinet

Falk

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

380

266

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In a 3D model mimicking realistic Cu 64 Zr 36 metallic glass, we uncovered a direct link between the quasi-localized low-frequency vibrational modes and the local atomic packing structure. We also demonstrate that quasi-localized soft modes correlate strongly with fertile sites for shear transformations: geometrically unfavored motifs constitute the most flexible local environments that encourage soft modes and high propensity for shear transformations, whereas local configurations preferred in this alloy, i.e., the full icosahedra (around Cu) and Z16 Kasper polyhedra (around Zr), contribute the least.liquid-like regions | heterogeneity | structure-property relationship | uncommon motifs | shear transformation zones M etallic glasses (MGs) have an inherently inhomogeneous internal structure, with a wide spectrum of atomic-packing heterogeneities (1-4). As a result, an a priori identification of structural defects that carry atomic rearrangements (strains) under imposed stimuli such as temperature and externally applied stresses has always been a major challenge (3-6). In several quasi-2D or 3D models of amorphous solids (such as jammed packings of soft spheres interacting via repulsive potentials or colloidal particles), low-frequency vibrational normal modes have been characterized, and it has recently been demonstrated that some of these modes are quasilocalized (7)(8)(9)(10)(11)(12)(13)(14). A population of "soft spots" has been identified among them in terms of their low-energy barriers for local rearrangements (13,14), correlating also with properties in supercooled liquids such as dynamic heterogeneity (15-17). However, it is not certain where the soft spots are in realistic MGs (18), in terms of an explicit correlation with local atomic packing and topological arrangements (18)(19)(20). In particular, there is a pressing need to determine whether it is possible to identify shear transformation zones, i.e., the local defects that carry inelastic deformation (21,22). Accomplishing this would permit the characterization of MG microstructure in a way that directly ties atomic configuration with mechanical response beyond the elastic regime. We will show here that there is indeed a correlation between soft modes and atoms that undergo shear transformations, and both have their structural signature in specific atomic packing environments defined in terms of coordination polyhedra (3). Fig. 1 displays the vibrational density of states (V-DOS), D(ω), calculated from the eigen-frequencies obtained by normal mode analysis of the Cu 64 Zr 36 MG prepared with a cooling rate of 10 9 K/s (Methods). The main peak stays around 14 meV and becomes only slightly narrower (or wider) when the cooling rate used to prepare the MG is slower (or faster), as seen in Fig. S1; the glasses cooled at slower rates exhibit fewer low-frequency (or low-energy) vibrational modes. The blue portion in Fig. 1 indicates the 1% lowest-frequency normal modes, which will be summed over in our calculations of the participation fraction, P i , in s...

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Section: Significancementioning

confidence: 93%

Soft spots and their structural signature in a metallic glass

Ding

Patinet

Falk

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

380

266

View full text Add to dashboard Cite

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“…Whereas those studies have offered insight into the details of the atom rearrangement under an imposed shear stress for specific interatomic potentials, the system sizes are small and the strain rates are exceedingly high so that the direct application of the findings to actual experimental conditions is somewhat unclear. Moreover, recent experimental studies have revealed the presence of nanoscale spatial heterogeneities in amorphous alloys that have not been considered in the simulations, but may affect deformation (21)(22)(23)(24)(25)(26).…”

mentioning

confidence: 99%

Nucleation of shear bands in amorphous alloys

Perepezko

Imhoff

Chen

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

106

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The initiation and propagation of shear bands is an important mode of localized inhomogeneous deformation that occurs in a wide range of materials. In metallic glasses, shear band development is considered to center on a structural heterogeneity, a shear transformation zone that evolves into a rapidly propagating shear band under a shear stress above a threshold. Deformation by shear bands is a nucleation-controlled process, but the initiation process is unclear. Here we use nanoindentation to probe shear band nucleation during loading by measuring the first pop-in event in the load-depth curve which is demonstrated to be associated with shear band formation. We analyze a large number of independent measurements on four different bulk metallic glasses (BMGs) alloys and reveal the operation of a bimodal distribution of the first pop-in loads that are associated with different shear band nucleation sites that operate at different stress levels below the glass transition temperature, T g . The nucleation kinetics, the nucleation barriers, and the density for each site type have been determined. The discovery of multiple shear band nucleation sites challenges the current view of nucleation at a single type of site and offers opportunities for controlling the ductility of BMG alloys.plastic deformation | stochastic analysis D eformation by shear bands occurs in both crystalline and amorphous phases over a wide range of size scales. In geological materials with a granular nature such as sand (1, 2) or within rocks, shear bands are of macroscopic size (3); in polymers and crystalline metals, shear bands are several micrometers in size; in metallic glasses (MGs), shear bands are of the order of 10-20 nm in thickness (4). The onset of shear bands in metallic glasses represents initial plastic yielding and induces a highly localized plastic flow that limits ductility and is responsible for strain softening (4, 5). Because shear bands directly determine the capability of an amorphous phase to sustain plastic flow and exhibit ductile behavior, there have been numerous studies on the propagation of shear bands to promote shear band branching and additional nucleation to achieve useful ductility (6-9). On a microscopic scale, the initiation of shear bands in MGs is considered to be controlled by the activation of a shear transformation zone (STZ) (10, 11) that represents a localized atomic arrangement. The STZs are activated by a two-stage process starting with a flow-induced dilatation that broadens homogeneously in the initial stage, but subsequently narrows into a shear band autocatalytically at the expense of shear flow in the surrounding material (10, 12). The localization of plastic flow would become predominant at low temperatures because the diffusive atomic rearrangements are too slow to disperse the dilatation effect quickly enough. Clearly, the nucleation of shear bands is of critical importance in the deformation behavior, but the detailed examination of the nucleation kinetics behavior has received only limited s...

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“…83 With the single cycle method however, and by monitoring the wave prole of the cantilever at a nite number of locations on its longitudinal axis, transient phenomena can be probed, in principle, with sub-microsecond resolution. A discussion about the high temporal resolution of the method is given in terms of its potential to be employed experimentally to probe fast processes from those involved in phase transformation 84 and other irreversible interactions 23 to complex and fast biological phenomena. 9,81,85,86 In the conclusions, the experimental challenges involving implementation are put into context and related to current developments in advanced dAFM methods.…”

mentioning

confidence: 99%

Single cycle and transient force measurements in dynamic atomic force microscopy

Gadelrab¹,

Santos²,

Font

et al. 2013

Nanoscale

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The monitoring of the deflection of a micro-cantilever, as the end of a sharp probe mounted at its end, i.e. the tip, interacts with a surface, forms the foundation of atomic force microscopy AFM. In a nutshell, developments in the field are driven by the requirement of obtaining ever increasing throughput and sensitivity, and enhancing the versatility of the instrument to simultaneously map the topography and quantify nanoscale processes and properties. In the most common dynamic mode of operation, the motion of the driven cantilever is monitored at a single point on its longitudinal axis. Here, we show that from this single point a waveform is obtained that contains all the details about conservative and dissipative interactions. Then a formalism that accounts for multiple arbitrary flexural modes is developed for an indirectly driven cantilever. The formalism is shown to allow recovery of the details of the interaction even in the presence of complex and relevant hysteretic forces when the cantilever oscillates in the steady state. In a different approach, we develop a formalism that monitors the wave profile of the cantilever, i.e. the waveform at five different points on its longitudinal axis. With this formalism the interaction can be reconstructed during a single oscillation cycle even in the transient state of oscillation. Finally, we discuss the potential and advantages of the proposed methods and future technical challenges. Other standard and state of the art techniques and methods are also discussed and compared with the ones presented here. This work should also provide insight into the current high throughput-high sensitivity developments dealing with multifrequency dynamic AFM where information is recovered from multiple eigenmodes.

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Characterization of Nanoscale Mechanical Heterogeneity in a Metallic Glass by Dynamic Force Microscopy

Cited by 372 publications

References 34 publications

Soft spots and their structural signature in a metallic glass

Soft spots and their structural signature in a metallic glass

Nucleation of shear bands in amorphous alloys

Single cycle and transient force measurements in dynamic atomic force microscopy

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