Measuring surface dislocation nucleation in defect-scarce nanostructures

Abstract

Linear defects in crystalline materials, known as dislocations, are central to the understanding of plastic deformation and mechanical strength, as well as control of performance in a variety of electronic and photonic materials. Despite nearly a century of research on dislocation structure and interactions, measurements of the energetics and kinetics of dislocation nucleation have not been possible, as synthesizing and testing pristine crystals absent of defects has been prohibitively challenging. Here, we report experiments that directly measure the surface dislocation nucleation strengths in high-quality 〈110〉 Pd nanowhiskers subjected to uniaxial tension. We find that, whereas nucleation strengths are weakly size- and strain-rate-dependent, a strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure atomic-scale activation volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model.

Mechanism transition and strong temperature dependence of dislocation nucleation from grain boundaries: An accelerated molecular dynamics study

“…Dislocation nucleation from interfacial defects dominate plastic deformation of materials in a confined volume, which may have a limited number of plastic deformation carriers [1][2][3][4]. For example, plastic deformation of nanocrystalline metals, which exhibit high strength, is governed by a dislocationnucleation event from grain boundaries (GBs) [5].…”

“…Thus in this study we accelerate the dislocation-nucleation events using adaptive-boost MD (ABMD) [16,17] and study the dislocation nucleation with atomic-level resolution at finite temperature, which offers opportunities for more comprehensive investigation of these processes arising from interfacial defects. Note that while the temperature and strain-rate dependences of dislocation nucle-ation from surfaces have been studied using both atomistic modeling [18] and experiments [4], those of dislocation nucleation from GBs have not been studied yet. Hence, although the dislocation-nucleation mechanism has been often studied using typical MD simulation, the fundamental mechanisms are unfortunately not fully understood.…”

Effect of Structural Heterogeneity of 17Mn1Si Steel on the Temperature Dependence of Impact Deformation and Fracture

“…Structural heterogeneities serve as preferred sites for plastic flow initiation, generation of lattice and boundary defects and discontinuities of various types [9][10][11]. A pre-defined structural level of deformation is associated naturally with a free surface where deformation takes place first [12][13][14][15][16]. The nonlinearity of the deformation processes can be taken into account by considering an independent 2D subsystem (surface layer and internal interfaces) and a 3D crystalline subsystem (grain interior).…”

Surface Rebound of Relativistic Dislocations Directly and Efficiently Initiates Deformation Twinning

“…Such strongly correlated DT mode requires extremely stringent spatial and temporal coordination of twinning dislocations (the right type of partial dislocations on consecutive atomic planes one after another [8]). This is hardly possible by the conventional pole mechanism [9,10] due to the pristine nature of the deformation volume, nor by the generally believed thermally activated nucleation (TAN) [2,[5][6][7][11][12][13] due to possible long waiting time.In the following, we illustrate that while the first dislocation to initiate DT must come from a TAN event, subsequent twinning dislocations can be generated by dislocations running at speeds near the transverse sound speed (c t ). Specifically, twinning dislocations are generated successively on each and every consecutive atomic plane by a surfacerebound sustained (SRS) nucleation process, in a domino cascade fashion.…”

“…Recent advances in small-volume materials fabrication have created a remarkable category of metallic crystals that can retain pristine crystal structures on the length scale of 10 1 − 10 2 nanometers [1][2][3][4][5][6][7]. Deformation twinning (DT) has been shown to initiate in these metals at ultrahigh stresses (∼10 −2 G, where G is shear modulus) and on a very short time scale (≪0.01 s, the typical time resolution of state-of-the-art in situ microscopy imaging techniques) [2,[4][5][6], indicating strong spatial-temporal correlations in the underlying dislocation dynamics.…”