The influence of solute on irradiation damage evolution in nanocrystalline thin-films

https://doi.org/10.1016/j.jnucmat.2020.152616Get rights and content

Highlights

  • Irradiation induced defect densities did not demonstrate an immediate correlation to grain size.

  • Sample composition was found to affect defect evolution in nanocrystalline systems.

  • Average defect cluster size ubiquitously decreases as grain size decreases.

  • Solute addition inhibits defect kinetics and impedes defect agglomeration, i.e. smaller defect cluster size.

Abstract

Grain boundaries (GBs) are considered sinks where mobile defects are attracted and annihilated thereby hampering irradiation damage accumulation. Nanocrystalline (NC) metals characteristically have greater densities of GBs relative to their coarse-grained counterparts hence they are postulated to provide enhanced resistance to irradiation damage.

The use of alloying as a means to impart synergistic properties such as corrosion resistance, increased toughness, or improved conductivity is well studied, yet the cooperative effects of solute addition and grain size in the nano-regime is not well understood. In this study, a combination of in situ ion irradiation, transmission electron microscopy (TEM), and automated crystal orientation mapping (ACOM) on model Ni, NiCr, Fe, and FeCr NC thin-films are used to provide experimental evidence that grain size and irradiation induced defect morphology (defect density and size) are not directly correlated due to defect agglomeration, annihilation at sinks, and saturation, while the addition of solute impedes defect mobility, altering the final damage state.

Introduction

The development of materials that can better withstand the operating environment within nuclear reactors is of critical importance for the longevity of existing reactors and the robustness of future nuclear energy systems [1]. Structural components in reactors are exposed to extreme conditions such as radiation and high temperatures often in aqueous surroundings, therefore, rugged alloys, such as stainless steels, are often selected for constituent materials due to the necessity of resistance to hardening, embrittlement, swelling, and corrosion [1,2]. Radiation damage fostered by extreme environments emerges in the form of irradiation-induced point defect production. These point defects can be mobile and are able to agglomerate, annihilate, and interact with other defects and interfaces; subsequently, the defect concentration and furthermore the material microstructure is incessantly in flux. High densities of radiation-induced defects can compromise the structural integrity of the material, substantially degrading the mechanical properties of components. Thus, it is a necessity to obtain a fundamental understanding of the evolution of irradiation-induced defects to develop radiation resistant materials.

Nanocrystalline (NC) materials have a large volume fraction of grain boundaries (GB) compared to their coarse grain analogs. GBs are considered sinks for irradiation-induced defects [3], [4], [5], [6], hence it is conjectured that NC metals should exhibit significant reductions in radiation damage as a result of the limited mean free path for migrating defects to travel and be absorbed within a NC matrix [7,8]. Early investigations utilizing transmission electron microscopy (TEM) and x-ray diffuse scattering determined that defect size and density increase with increasing irradiation damage dose [9], [10], [11]; furthermore, Sun et al. found that the density and diameter of dislocation loops in NC Ni was nearly half of those in coarse-grained Ni when irradiated with Kr ions up to 5 dpa [12]. From a positron annihilation spectroscopy experiment, Tsuchida et al. concluded that defect accumulation was suppressed in C ion irradiated NC Ni, whereas the vacancy concentration was enhanced during irradiation in coarse-grained Ni [13]. Simulations have also been used to investigate how collision cascades interact with GBs. Using atomic scale modeling techniques, Samaras et al. [14], [15], [16], [17] concluded that GBs in NC systems preferentially absorb interstitials leaving a defect structure primarily consisting of vacancies in the grain interior and in higher quantities than for equivalent cascades in a single crystal. Mechanistic insights concerning defect evolution explored by Bai and Uberuaga et al. [18,19], and Demkowicz et al. [20] reveal that GBs serve as reservoirs for collision cascade-produced interstitials. Energy barriers for interstitial migration are lowered by the interstitial-rich GBs, which efficiently emit interstitials and interact with nearby vacancies, thereby enhancing interstitial-vacancy recombination [21,22]. In a proceeding study, Jin et al. went on to show that the effect of GBs on defect annihilation was not limited to discrete vacancies but gave rise to a drastic decrease in the density of defect clusters in small grain spacings [23].

Several experimental and theoretical studies have examined the radiation resistance of NC materials, but discrete data on the trends of defect densities and defect sizes within the nano-regime is sparse and inconsistent. In a study by Rose et al. [24], NC Pd and ZrO2 irradiated with Kr ions exhibited consistent dramatic reductions in defect cluster densities as grain sizes decreased from 100 nm to below 50 nm, and no defect clusters were observed in NC grains of Pd <30 nm and ZrO2 <15 nm. Contrary to Rose's findings, in an experiment comparing ultrafine grain tungsten samples irradiated with Si, Cu, and W ions, El-Atwani et al. [25] found no clear trend in the data distribution relating defect density as a function of the grain size in the nano- and ultrafine regimes. Counterintuitively, there was a decreasing trend observed spanning from the ultrafine gain (200+ nm) to micron range. In a similar study on He irradiated NC Fe, El-Atwani found that the defect density demonstrated a slow increasing trend as a function of grain size in the NC regime and scattering at the regime transition from the NC to the ultra-fine regime [26]. They also confirmed the occurrence of loop coalescence by comparing defect density and size as a function of irradiation dose. Moreover, it has been conjectured that the rapid and efficient absorption of dislocations by GBs results in higher radiation tolerance in small grains due to higher interstitial storage at GBs and defect recombination in the grain interior [27]; nonetheless, the lack of consistent defect density trends in irradiation studies in the NC regime has been suggested to be an artifact of differences in the stability and mobility of defects [28].

To date, few studies have reported data correlating irradiation induced defect density and size to grain size, hence definitive answers of whether NC materials will exhibit enhanced radiation tolerance as grain size decreases remains unresolved [29]. In this study, the use of in situ TEM irradiation and ACOM (automated crystal orientation mapping) was employed to investigate the influence of irradiation on the microstructure of NC metals relating defect density and average defect size to grain size. Defect density and average size is examined as a function of grain size in four different materials: Ni and Fe were chosen as surrogate model fcc and bcc, respectively, metals for irradiation studies, and Ni-5%Cr and Fe-9%Cr (henceforward referred to as NiCr and FeCr) were examined to investigate the effect of solute atoms in the matrix. Our results show that the average defect size decreases as grain size decreases, although, there is no coherent trend correlating irradiation induced defect density to grain size due to defect agglomeration and saturation.

Section snippets

Experimental methods

NC Ni, NiCr (5 atomic percent Cr), Fe, and FeCr (9 atomic percent Cr) thin-films were prepared via physical vapor deposition onto NaCl substrates [30] then floated off onto 3 mm TEM grids. Thin-film composition was measured using XRF; the films had nominal thickness of ~100 nm, and an as-deposited average grain size of ~10 nm. Once on the TEM grids, the samples were annealed in vacuum using a Gatan 628 TEM heating holder to obtain desired grain size and refined grain structure while also

Microstructure type

The Ni, Fe, NiCr and FeCr thin-films were composed of randomly oriented grains with grain sizes ranging from 20 to 200 nm. The reported grain sizes are measured as the area of a polygon defined by the GBs of the given grain. The average grain size of the Ni was ~70 nm and ~35 nm for Fe. Though the NiCr and FeCr films were annealed at higher temperatures than the pure metal films, grain growth stabilized at a smaller size of ~50 nm and ~30 nm, respectively; this is attributed to the pinning

Conclusion

Similar to findings in coarse grain studies, sample composition was found to affect defect evolution in NC systems with more complex solid solutions exhibiting smaller defect clusters; however, the density of irradiation induced defects did not demonstrate an immediate correlation to grain size. An increasing trend in average defect cluster size as grain size increases is distinct for all sample compositions and doses, while the average defect density decreases with increasing damage dose. This

Credit author statement

James E. Nathaniel II, wrote the manuscript, conducted experiments, and analyzed data

Gregory A. Vetterick, conducted experiments and analyzed data

Osman El-Atwani, conducted experiments

Asher Leff, conducted experiments

Jon Kevin Baldwin, synthesized thin-film specimens

Pete Baldo, operated accelerator for irradiation

Marquis A. Kirk, Khalid Hattar, and Mitra L. Taheri, supervised study

Data availability

The raw data required to reproduce these findings can be made available upon request. The processed data required to reproduce these findings can be made available upon request.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

J.N. would like to express appreciation to Emily Hopkins for assistance with refining the manuscript. M.L.T., J.N., G.V., O.E., and A.L. acknowledge funding from the US Department of Energy (DOE) Basic Energy Sciences (BES) program under Grant DE-SC0008274. M.L.T. and J.N. also acknowledge funding in part from U.S. DOE, BES through contract DE-SC0020314. KH was also supported by the U.S. DOE BES Materials Science and Engineering Division, but under a separate FWP 15013170. Access to the in situ

References (66)

  • M. Samaras et al.

    Stacking fault tetrahedra formation in the neighbourhood of grain boundaries

    Nucl. Instruments Methods Phys. Res. B.

    (2003)
  • M. Jin et al.

    Radiation damage reduction by grain-boundary biased defect migration in nanocrystalline Cu

    Acta Mater

    (2018)
  • M. Rose et al.

    Instability of irradiation induced defects in nanostructured materials

    Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms.

    (1997)
  • O. El-atwani et al.

    In-situ TEM / heavy ion irradiation on ultra fi ne-and nanocrystalline-grained tungsten : Effect of 3 MeV Si, Cu and W ions

    Mater. Charact

    (2015)
  • O. El-atwani et al.

    Unprecedented irradiation resistance of nanocrystalline tungsten with equiaxed nanocrystalline grains to dislocation loop accumulation

    Acta Mater

    (2019)
  • K. Hattar et al.

    Concurrent in situ ion irradiation transmission electron microscope

    Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms.

    (2014)
  • R.E. Stoller et al.

    On the use of SRIM for computing radiation damage exposure

    Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms.

    (2013)
  • K.Y. Yu et al.

    In situ studies of irradiation-induced twin boundary migration in nanotwinned Ag

    Scr. Mater.

    (2013)
  • M.L. Jenkins

    Characterisation of radiation-damage microstructures by TEM

    J. Nucl. Mater.

    (1994)
  • J.E. Nathaniel et al.

    Toward high-throughput defect density quanti fi cation: A comparison of techniques for irradiated samples

    Ultramicroscopy

    (2019)
  • F. Bley

    Neutron small-angle scattering study of unmixing in FeCr alloys

    Acta Metall. Mater.

    (1992)
  • M.H. Mathon et al.

    A SANS investigation of the irradiation-enhanced a – a’ phases separation in 7 – 12 Cr martensitic steels

    J. Nucl. Mater.

    (2003)
  • D. Brimbal et al.

    Single- and dual-beam in situ irradiations of high-purity iron in a transmission electron microscope: Effects of heavy ion irradiation and helium injection

    Acta Mater

    (2014)
  • D.S. Aidhy et al.

    Point defect evolution in Ni, NiFe and NiCr alloys from atomistic simulations and irradiation experiments

    Acta Mater

    (2015)
  • M.W. Ullah et al.

    Damage accumulation in ion-irradiated Ni-based concentrated solid-solution alloys

    Acta Mater

    (2016)
  • S.A. Briggs et al.

    Observations of defect structure evolution in proton and Ni ion irradiated Ni-Cr binary alloys

    J. Nucl. Mater.

    (2016)
  • M. Jin et al.

    Thermodynamic mixing energy and heterogeneous diffusion uncover the mechanisms of radiation damage reduction in single-phase Ni-Fe alloys

    Acta Mater

    (2018)
  • C.M. Barr et al.

    Anisotropic radiation-induced segregation in 316L austenitic stainless steel with grain boundary character

    Acta Mater

    (2014)
  • T.S. Duh et al.

    Effects of Grain Boundary Misorientation on the Solute Segregation in austenitic stainless steels

    J. Nucl. Mater.

    (1998)
  • S. Watanabe et al.

    Sink effect of grain boundary on radiation-induced segregation in austenitic stainless steel

    J. Nucl. Mater.

    (2000)
  • N. Sakaguchi et al.

    Radiation-induced segregation and corrosion behavior on ∑3 coincidence site lattice and random grain boundaries in proton-irradiated type-316L austenitic stainless steel

    J. Nucl. Mater.

    (2013)
  • R. Zhu et al.

    The relationship between micro-structural evolution and deformation mechanisms for nanocrystalline Ni under high strain rate

    Mater. Sci. Eng. A.

    (2016)
  • C. Jiang et al.

    Effect of Grain Boundary Stresses on Sink Strength

    Mater. Res. Lett.

    (2014)
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