Fatigue-induced grain coarsening in nanocrystalline platinum films

Meirom, Roi A.; Alsem, Daan Hein; Romasco, Amber L.; Clark, Trevor; Polcawich, Ronald G.; Pulskamp, Jeffrey S.; Dubey, Madan; Ritchie, Robert O.; Muhlstein, Christopher L.

doi:10.1016/j.actamat.2010.10.047

Cited by 56 publications

(30 citation statements)

References 31 publications

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“…On the contrary, Kumar et al [409] did not observe any formation of fatigue cracks after 10 million cycles in Al thin films when deformed cyclically with maximum applied strain equal to 0.4%. Meirom et al [342] measured the Da/DN versus DK response in 1 lm thick Pt films involving either very elongated columnar grains or multiple equiaxed grains along the thickness (these two morphologies exhibit almost identical uniaxial stress strain response), see also [410]. The fatigue crack resistance was found independent of the grain morphology.…”

Section: Fatiguementioning

confidence: 95%

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: Fatiguementioning

confidence: 95%

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

2016

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“…Further investigation indicated that tensile strains did not result from the thermoforming process, but instead were induced during insertion of the microwire mold into the preformed Parylene channel; electrodes that encountered compressive stresses did not exhibit any cracks [43]. It is important that mold-induced mechanical strains do not exceed the ultimate yield strains for the device materials (0.03 for thin film platinum [44]). In the case of these Parylene micro-cones, the strain limit was reached at a radius of curvature of ∼240 µm, obtained using finite element modeling (data not shown; fabricated cones had radii of 30-90 µm).…”

Section: Dmentioning

confidence: 99%

Formation of three-dimensional Parylene C structures via thermoforming

Kim

Chen

Gupta

et al. 2014

J. Micromech. Microeng.

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The thermoplastic nature of Parylene C is leveraged to enable the formation of three-dimensional structures using a thermal forming (thermoforming) technique. Thermoforming involves the heating of Parylene films above its glass transition temperature while they are physically confined in the final desired conformation. Micro and macro scale three-dimensional structures composed of Parylene thin films were developed using the thermoforming process, and the resulting chemical and mechanical changes to the films were characterized. No large changes to the surface and bulk chemistries of the polymer were observed following the thermoforming process conducted in vacuum. Heat treated structures exhibited increased stiffness by a maximum of 37% depending on the treatment temperature, due to an increase in crystallinity of the Parylene polymer. This study revealed important property changes resulting from the process, namely (1) the development of high strains in thermoformed areas of small radii of curvature (30-90 µm) and (2) ∼1.5% bulk material shrinkage in thermoformed multilayered Parylene-Parylene and Parylene-metal-Parylene films. Thermoforming is a simple process whereby three-dimensional structures can be achieved from Parylene C-based thin film structures with tunable mechanical properties as a function of treatment temperature.

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“…[37][38][39][40][41][42][43][44] Such mechanisms leading directly to plastic deformation were first experimentally shown in 1957 by Li et al 45,46 to be active during room temperature deformation of materials possessing low-angle GBs. Extensions to high-angle GBs where a dislocation-based description 47 is incomplete, however, have been the subject of more recent research.…”

Section: Introductionmentioning

confidence: 99%

The role of confinement on stress-driven grain boundary motion in nanocrystalline aluminum thin films

Gianola

Farkas

Gamarra

et al. 2012

Journal of Applied Physics

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The role of confinement on stress-driven grain boundary motion in nanocrystalline aluminum thin films 3D molecular dynamics simulations are performed to investigate the role of microstructural confinement on room temperature stress-driven grain boundary (GB) motion for a general population of GBs in nanocrystalline Al thin films. Detailed analysis and comparison with experimental results reveal how coupled GB migration and GB sliding are manifested in realistic nanoscale networks of GBs. The proximity of free surfaces to GBs plays a significant role in their mobility and results in unique surface topography evolution. We highlight the effects of microstructural features, such as triple junctions, as constraints to otherwise uninhibited GB motion. We also study the pinning effects of impurities segregated to GBs that hinder their motion. Finally, the implications of GB motion as a deformation mechanism governing the mechanical behavior of nanocrystalline materials are discussed. V C 2012 American Institute of Physics.[http://dx

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Fatigue-induced grain coarsening in nanocrystalline platinum films

Cited by 56 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

Formation of three-dimensional Parylene C structures via thermoforming

The role of confinement on stress-driven grain boundary motion in nanocrystalline aluminum thin films

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