Texture dependent strain rate sensitivity of ultrafine-grained aluminum films

Materials Research Letters

Ebner

Izadi

et al. 2016

Self Cite

We used a novel diffraction-based method to extract the local, atomic-level elastic strain in nanoscale amorphous TiAl films during in situ transmission electron microscopy deformation, while simultaneously measuring the macroscopic strain. The complementary strain measurements revealed significant anelastic deformation, which was independently confirmed by strain rate experiments. Furthermore, the distribution of first nearest-neighbor distances became narrower during loading and permanent changes were observed in the atomic structure upon unloading, even in the absence of macroscopic plasticity. The results demonstrate the capability of in situ electron diffraction to probe structural rearrangements and decouple elastic and anelastic deformation in metallic glasses.

Section: Methodsmentioning

confidence: 99%

Revealing anelasticity and structural rearrangements in nanoscale metallic glass films using in situ TEM diffraction

Materials Research Letters

Ebner

Izadi

et al. 2016

Self Cite

“…The BE ratio for the non-textured film was 0.27. For completeness, we also show the stress-strain response of another non-textured film at different strain rates [15] in Fig. 3b.…”

Section: Ex Situ Experimentsmentioning

confidence: 99%

“…In addition to grain size, texture has also been shown to significantly influence the mechanical behavior of UFG/NC metal films [13]- [16]. Experimental investigations on UFG Al films with similar thickness and mean grain sizes but different textures have revealed notable changes in flow stress and inelastic strain recovery during unloading [13], [15]. Similarly, it has been reported that the variation of texture in NC Ni foils leads to a distinct change of the yield stress and ultimate strength [8].…”

Section: Introductionmentioning

confidence: 99%

“…The primary objective of this study was to understand the deformation mechanisms in UFG Al films that have a random orientation of grains (no preferred texture). The study was motivated by recent experiments which showed that non-textured UFG Al films have an unusually large SRS exponent (m = 0.107), possibly caused by time dependent grain rotations [15]. Here, we used a combination of in situ and ex situ quasi-static, load-unload experiments to further explore the deformation behavior of such films.…”

Section: Introductionmentioning

confidence: 99%

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Grain rotations in ultrafine-grained aluminum films studied using in situ TEM straining with automated crystal orientation mapping

Izadi

Darbal²,

et al. 2017

Materials & Design

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In situ TEM straining allows probing deformation mechanisms of ultrafine-grained and nanocrystalline metals. While obtaining statistically meaningful information about microstructural changes using conventional bright-field/dark-field imaging or diffraction is time consuming, automated crystal orientation mapping in TEM (ACOM-TEM) enables tracking orientation changes of hundreds of grains simultaneously. We use this technique to uncover extensive grain rotations during in situ tensile deformation of a freestanding, ultrafine-grained aluminum film (thickness 200 nm, mean grain size 180 nm). During loading, both the fraction of grains that undergo rotations and the magnitude of their rotations increase with strain. The rotations are partially or fully reversible in a significant fraction of grains during unloading, leading to notable inelastic strain recovery. More surprisingly, the direction of rotation remains unchanged for a small fraction of grains during unloading, despite a sharp reduction in the applied stress. The ACOM-TEM measurements also provide evidence of reversible and irreversible grain/twin boundary migrations in the film. These microstructural observations point to a highly inhomogeneous and constantly evolving stress distribution in the film during both loading and unloading.

“…Therefore, the ability to robustly control the microstructure (mean size, orientation, size dispersion and spatial distribution of grains) of nanostructured films/coatings would enable us to optimize their mechanical properties and enhance their performance. Physical vapor deposition (PVD) processes, which are most commonly used to synthesize high quality nanostructured thin films, allow us to vary the texture [1] and mean grain size [2] by changing the film thickness, substrate, deposition rate or temperature [3]. Never- theless, in PVD-synthesized films it is difficult to decouple the mean grain size and thickness and there is little control over grain size dispersion or spatial distribution.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of thin films with highly tailored microstructures

Materials Research Letters

Rajagopalan

2018

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We report a new methodology to synthesize thin films with exceptional microstructural control via systematic, in-situ seeding of nanocrystals into amorphous precursor films. When the amorphous films are subsequently crystallized by thermal annealing, the nanocrystals serve as preferential grain nucleation sites and control their micro/nanostructure. We demonstrate the capability of this methodology by precisely tailoring the size, geometry and spatial distribution of nanostructured grains in structural (TiAl) as well as functional (TiNi) thin films. This synthesis methodology is likely to be applicable to other amorphously grown materials and enables explicit microstructural control in a wide spectrum of thin films/coatings. IMPACT STATEMENTThis paper describes a novel synthesis methodology to precisely tailor the microstructure of thin films and reveals the mechanisms underlying this methodology using in-situ TEM annealing experiments. ARTICLE HISTORY