Texture evolution in nanocrystalline iron films deposited using biased magnetron sputtering

Vetterick, G.; Baldwin, J. Kevin; Misra, Amit; Taheri, Mitra L.

doi:10.1063/1.4904077

Cited by 20 publications

(9 citation statements)

References 39 publications

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“…Fe films were sputter deposited on NaCl substrates and then floated onto molybdenum TEM grids. Details about the sputtering target, the sputtering process, purity of the films and the TEM sample preparation method are described elsewhere 28 , 35 . The films were then annealed in situ in a JEOL 2100 LaB 6 TEM using a Gatan heating stage at 873 K for 600 seconds (with a ramp rate of 30 degrees per minute), while monitoring the grain growth to achieve well-defined grain boundaries without eliminating the nanocrystalline microstructure.…”

Section: Methodsmentioning

confidence: 99%

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

El-Atwani

Nathaniel

Leff

et al. 2017

Sci Rep

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Crystal defects generated during irradiation can result in severe changes in morphology and an overall degradation of mechanical properties in a given material. Nanomaterials have been proposed as radiation damage tolerant materials, due to the hypothesis that defect density decreases with grain size refinement due to the increase in grain boundary surface area. The lower defect density should arise from grain boundary-point defect absorption and enhancement of interstitial-vacancy annihilation. In this study, low energy helium ion irradiation on free-standing iron thin films were performed at 573 K. Interstitial loops of a 0/2 [111] Burgers vector were directly observed as a result of the displacement damage. Loop density trends with grain size demonstrated an increase in the nanocrystalline (<100 nm) regime, but scattered behavior in the transition from the nanocrystalline to the ultra-fine regime (100–500 nm). To examine the validity of such trends, loop density and area for different grains at various irradiation doses were compared and revealed efficient defect absorption in the nanocrystalline grain size regime, but loop coalescence in the ultra-fine grain size regime. A relationship between the denuded zone formation, a measure of grain boundary absorption efficiency, grain size, grain boundary type and misorientation angle is determined.

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Section: Methodsmentioning

confidence: 99%

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

El-Atwani

Nathaniel

Leff

et al. 2017

Sci Rep

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“…The iron films were deposited using magnetron sputtering of high purity iron onto sodium chloride substrates at Los Alamos National Laboratory 50 . Physical vapor deposition, like many bottom-up production methods for nanocrystalline materials, can result in the formation of non-equilibrium grain boundaries, especially when performed at low temperatures.…”

Section: Methodsmentioning

confidence: 99%

Achieving Radiation Tolerance through Non-Equilibrium Grain Boundary Structures

Vetterick

Gruber

Suri

et al. 2017

Sci Rep

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Many methods used to produce nanocrystalline (NC) materials leave behind non-equilibrium grain boundaries (GBs) containing excess free volume and higher energy than their equilibrium counterparts with identical 5 degrees of freedom. Since non-equilibrium GBs have increased amounts of both strain and free volume, these boundaries may act as more efficient sinks for the excess interstitials and vacancies produced in a material under irradiation as compared to equilibrium GBs. The relative sink strengths of equilibrium and non-equilibrium GBs were explored by comparing the behavior of annealed (equilibrium) and as-deposited (non-equilibrium) NC iron films on irradiation. These results were coupled with atomistic simulations to better reveal the underlying processes occurring on timescales too short to capture using in situ TEM. After irradiation, NC iron with non-equilibrium GBs contains both a smaller number density of defect clusters and a smaller average defect cluster size. Simulations showed that excess free volume contribute to a decreased survival rate of point defects in cascades occurring adjacent to the GB and that these boundaries undergo less dramatic changes in structure upon irradiation. These results suggest that non-equilibrium GBs act as more efficient sinks for defects and could be utilized to create more radiation tolerant materials in future.

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“…In this work, in-situ irradiation was performed in a transmission electron microscope (TEM) on freestanding nanocrystalline Fe samples of less than 100 nm grain size. To form the nanocrystalline samples, Fe films was sputter-deposited on NaCl substrates [6]. TEM micrographs of the samples after annealing showed both equilibrium and non-equilibrium (high local strain manifested by strong extinction bands) boundaries adjacent to each other ( Figure.1), thus enabling the comparison between both boundary types.…”

mentioning

confidence: 99%

Effect of Grain Boundary Structure on Defect Absorption and Denuded Zone Formation in Irradiated Nanocrystalline Iron

et al. 2015

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The performance of nuclear materials in extreme environments poses important fundamental questions about the behavior of condensed matter under far-from-equilibrium conditions.[1] Nuclear materials are exposed to high heat flux and irradiation that alter their microstructure, mechanical properties, and performance.[2] To mitigate possible damage, the use of UltraFine (UF) and NanoCrystalline (NC) metals has been proposed, due to their high grain boundary densities that thus act as high defect and particle sinks, [3] and improve mechanical properties (strength and ductility).[4] While recent research has focused on the effect of grain boundary character [5] on the radiation tolerance, fundamental questions about the role of non-equilibrium grain boundaries in defect absorption in comparison with equilibrium grain boundaries have yet to be answered. Understanding the effect of the non-equilibrium boundary local strain in irregular defect absorption and denuded zone formation could be crucial in engineering polycrystalline materials of higher radiation tolerance that can sustain the severe environments of future nuclear reactor conditions. In this work, in-situ irradiation was performed in a transmission electron microscope (TEM) on freestanding nanocrystalline Fe samples of less than 100 nm grain size. To form the nanocrystalline samples, Fe films was sputter-deposited on NaCl substrates [6]. TEM micrographs of the samples after annealing showed both equilibrium and non-equilibrium (high local strain manifested by strong extinction bands) boundaries adjacent to each other ( Figure.1), thus enabling the comparison between both boundary types. The in-situ TEM irradiation experiments were performed using the i3TEM facility in the Department of Radiation Solid Interactions at Sandia National Laboratories. Crystallographic orientation microscopy (ACOM) was also performed via NanoMEGAS ASTAR precession diffraction (eg. Figure.2). Effect of defect absorption on grain boundary structure is studied through the in-situ irradiation/ACOM experiments. The findings provide fundamental aspects to be considered in engineering high radiation tolerant nanomaterials.

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Texture evolution in nanocrystalline iron films deposited using biased magnetron sputtering

Cited by 20 publications

References 39 publications

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

Achieving Radiation Tolerance through Non-Equilibrium Grain Boundary Structures

Effect of Grain Boundary Structure on Defect Absorption and Denuded Zone Formation in Irradiated Nanocrystalline Iron

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