Effect of crystal orientation on the size effects of nano-scale fcc metals

Bagheripoor, Mahdi; Klassen, Robert D.

doi:10.1080/02670836.2020.1839193

Cited by 3 publications

(3 citation statements)

References 81 publications

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“…In the case of simple shear loading, the obtained thresholds show dependence on the orientation of the sample in the loading device, which is in qualitative agreement with experimental results, e.g. [35,36]. Our study also reveals a strong link between the structure of the apparent yield surface and the lattice symmetry.…”

Section: Ideal Shear Strengthsupporting

confidence: 90%

“…Almost all dislocations mediating the explosive stress drop manage to escape to the boundaries, sometimes even producing pristine-topristine transition [16,34]. It was also observed that as the deformation volume of a material decreases, the effect of crystal orientation on the operative deformation mechanisms increases; in particular, the mechanical response of sub-micron defect-free nanopillars is different depending on whether they are deformed along high symmetry orientations or low symmetry orientations [35,36]. The compression tests on confined micropillars revealed higher (and therefore closer to theoretical limit) stresses of massive dislocation nucleation than in the presence of free surfaces [36,37].…”

Section: Introductionmentioning

confidence: 99%

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Discontinuous yielding of pristine micro-crystals

Salman¹,

Baggio²,

Bacroix³

et al. 2021

Comptes Rendus. Physique

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We study the mechanical response of a dislocation-free 2D crystal under homogenous shear using a new mesoscopic approach to crystal plasticity, a Landau-type theory, accounting for the global invariance of the energy in the space of strain tensors while operating with an infinite number of equivalent energy wells. The advantage of this approach is that it eliminates arbitrariness in dealing with topological transitions involved, for instance, in nucleation and annihilation of dislocations. We use discontinuous yielding of pristine micro-crystals as a benchmark problem for the new theory and show that the nature of the catastrophic instability, which in this setting inevitably follows the standard affine response, depends not only on lattice symmetry but also on the orientation of the crystal in the loading device. The ensuing dislocation avalanche involves cooperative dislocation nucleation, resulting in the formation of complex microstructures controlled by a nontrivial self-induced coupling between different plastic mechanisms.

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Section: Ideal Shear Strengthsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Discontinuous yielding of pristine micro-crystals

Salman¹,

Baggio²,

Bacroix³

et al. 2021

Comptes Rendus. Physique

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“…First, particles were selected for testing to achieve a range of particle diameters, but they clearly differed in other attributes, including crystallographic orientation and particle shape. Crystal orientation modifies the resolved shear stress for defects on particular crystal planes and also modifies the degree of spatial inhomogeneity of stress . Particle shape modifies various factors, including stress concentrations at corners, and the out-of-plane shape of FCC structures can influence which types of defects are favored .…”

Section: Resultsmentioning

confidence: 99%

Size-Dependent Role of Surfaces in the Deformation of Platinum Nanoparticles

et al. 2023

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The mechanical behavior of nanostructures is known to transition from a Hall-Petch-like “smaller-is-stronger” trend, explained by dislocation starvation, to an inverse Hall-Petch “smaller-is-weaker” trend, typically attributed to the effect of surface diffusion. Yet recent work on platinum nanowires demonstrated the persistence of the smaller-is-stronger behavior down to few-nanometer diameters. Here, we used in situ nanomechanical testing inside of a transmission electron microscope (TEM) to study the strength and deformation mechanisms of platinum nanoparticles, revealing the prominent and size-dependent role of surfaces. For larger particles with diameters from 41 nm down to approximately 9 nm, deformation was predominantly displacive yet still showed the smaller-is-weaker trend, suggesting a key role of surface curvature on dislocation nucleation. For particles below 9 nm, the weakening saturated to a constant value and particles deformed homogeneously, with shape recovery after load removal. Our high-resolution TEM videos revealed the role of surface atom migration in shape change during and after loading. During compression, the deformation was accommodated by atomic motion from lower-energy facets to higher-energy facets, which may indicate that it was governed by a confined-geometry equilibration; when the compression was removed, atom migration was reversed, and the original stress-free equilibrium shape was recovered.

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