In situ observations of crack arrest and bridging by nanoscale twins in copper thin films

Kim, Seong-Woong; Li, Xiaoyan; Gao, Huajian; Kumar, Satish

doi:10.1016/j.actamat.2012.02.002

Cited by 83 publications

(35 citation statements)

References 31 publications

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“…This is another example of the interest of bimodal structures, here to arrest cracks. Nanotwins have also the potential to improve the tearing resistance by a crack blunting and bridging mechanisms, as shown by Kim et al on Cu films [405], or by forcing crack blunting, deflection, twinning/detwinning and slip transmission across the CTBs such as recently found in Ag films [406]. Note that in the study by Kim et al [405], they found, in agreement with the beginning of the message of this section, a transition between brittle intergranular fracture and a ductile mechanism assisted by the nanotwin bridging mechanism when increasing thickness above 40 nm.…”

Section: Damage and Fracture In Freestanding Small Scale Metallic Sysmentioning

confidence: 87%

“…Nanotwins have also the potential to improve the tearing resistance by a crack blunting and bridging mechanisms, as shown by Kim et al on Cu films [405], or by forcing crack blunting, deflection, twinning/detwinning and slip transmission across the CTBs such as recently found in Ag films [406]. Note that in the study by Kim et al [405], they found, in agreement with the beginning of the message of this section, a transition between brittle intergranular fracture and a ductile mechanism assisted by the nanotwin bridging mechanism when increasing thickness above 40 nm. Kumar et al [407] observed an unexpected phase transformation in 200 nm thick Al films with 60 nm grain size, owing to the extremely large stresses building up as a result of the absence of dislocation activity and diffusion mechanisms, with a significant toughening potential.…”

Section: Damage and Fracture In Freestanding Small Scale Metallic Sysmentioning

confidence: 87%

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Failure of metals III: Fracture and fatigue of nanostructured metallic materials

2016

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a b s t r a c tPushing the internal or external dimensions of metallic alloys down to the nanometer scale gives rise to strong materials, though most often at the expense of a low ductility and a low resistance to cracking, with negative impact on the transfer to engineering applications. These characteristics are observed, with some exceptions, in bulk ultra-fine grained and nanocrystalline metals, nano-twinned metals, thin metallic coatings on substrates and freestanding thin metallic films and nanowires. This overview encompasses all these systems to reveal commonalities in the origins of the lack of ductility and fracture resistance, in factors governing fatigue resistance, and in ways to improve properties. After surveying the various processing methods and key deformation mechanisms, we systematically address the current state of the art in terms of plastic localization, damage, static and fatigue cracking, for three classes of systems: (1) bulk ultra-fine grained and nanocrystalline metals, (2) thin metallic films on substrates, and (3) 1D and 2D freestanding micro and nanoscale systems. In doing so, we aim to favour cross-fertilization between progress made in the fields of mechanics of thin films, nanomechanics, fundamental researches in bulk nanocrystalline metals and metallurgy to impart enhanced resistance to fracture and fatigue in high-strength nanostructured systems. This involves exploiting intrinsic mechanisms, e.g. to enhance hardening and rate-sensitivity so as to delay necking, or improve grain-boundary cohesion to resist intergranular cracks or voids. Extrinsic methods can also be utilized such as by hybridizing the metal with another material to delocalize the deformation -as practiced in stretchable electronics. Fatigue crack initiation is in principle improved by a fine structure, but at the expense of larger fatigue crack growth rates. Extrinsic toughening through hybridization allows arresting or bridging cracks. The content and discussions are based on experimental, theoretical and simulation results from the recent literature, and focus is laid on linking microstructure and physical mechanisms to the overall mechanical behavior.

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Section: Damage and Fracture In Freestanding Small Scale Metallic Sysmentioning

confidence: 87%

Section: Damage and Fracture In Freestanding Small Scale Metallic Sysmentioning

confidence: 87%

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

2016

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“…Early studies on the fatigue behaviors of NC metals have revealed a nanoscale mechanism [2,3], i.e., vacancies coalesce into nanovoids at the GBs in front of a crack tip, and then, the main crack advances by linking with these nanovoids. Over the past few years, nanotwinned (NT) metals, a new type of hierarchical nanostructured material, have attracted enormous research attention [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In such materials, high-density nanoscale twins are introduced into the sub-micron-sized grains and act as sub-structures that can not only confine the dislocation segment length but also store the mobile dislocations during deformation [7].…”

Section: Introductionmentioning

confidence: 99%

Atomistic mechanisms of fatigue in nanotwinned metals

Zhou

Chen

2015

Acta Materialia

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“…1(a) showing the h1 1 0i M and h1 1 0i T crack edges in the adjoining matrix (M) and twin (T) crystals. Kim et al [18] and Zhou and Qu [19] performed molecular dynamics (MD) simulations of fracture in thick nanotwinned samples. They observed the damage and fracture processes, including crack blunting through dislocation emission, crack bridging by twin lamella, crack deflection by grain boundaries, and nanovoid formation at the intersections between grain boundaries and twin boundaries.…”

Section: Introductionmentioning

confidence: 99%

“…Singh et al [16] measured the fracture toughness and fatigue crack growth in nanotwinned Cu processed by electrodeposition, and showed that the presence of nanotwins enhanced both monotonic and cyclic crack growth resistances. Shan et al [17] and Kim et al [18] used the in situ transmission electron microscopy (TEM) to directly observe crack growth in nanotwinned Cu. Fig.…”

Section: Introductionmentioning

confidence: 99%

Fracture in a thin film of nanotwinned copper

Zeng

Lü

et al. 2015

Acta Materialia

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a b s t r a c tNanotwinned Cu exhibits an unusual combination of ultra-high strength and high tensile ductility. However, its fracture behavior and associated microscopic mechanisms remain largely unexplored.Here we study the fracture in a free-standing thin film of nanotwinned Cu using molecular dynamics (MD) simulations. For a pre-crack inclined to the twin boundary, MD simulations show a characteristic fracture mode of zigzag cracking, which arises due to periodic deflections of the crack path by twin boundaries. The mechanism of fracture involves the screw dislocation-mediated local thinning ahead of the crack, instead of cleavage fracture. Importantly, MD simulations show a unique fracture footprint of h1 1 0i-oriented crack edges, consistent with the previous experimental observation from in situ transmission electron microscopy. Our results reveal the toughening mechanisms by nanotwins and also have broader implications for understanding the mechanical failure of metallic thin films.

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In situ observations of crack arrest and bridging by nanoscale twins in copper thin films

Cited by 83 publications

References 31 publications

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Atomistic mechanisms of fatigue in nanotwinned metals

Fracture in a thin film of nanotwinned copper

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