Irradiated Alloys Research Articles

Systematic study of radiation-induced segregation in neutron-irradiated FeCrAl alloys

This work systematically reports grain boundary radiation-induced segregation (RIS), and insights into RIS mechanisms, in FeCrAl alloys. Recently, FeCrAl alloys have received significant attention as direct replacement accident tolerant fuel (ATF) claddings for light water cooled nuclear reactors, because of their corrosion and high-temperature oxidation resistance characteristics. One degradation method not studied in detail is RIS, which could sufficiently alter grain boundary chemistry, potentially compromising the superior aqueous corrosion resistance. This study focuses on candidate ATF FeCrAl alloys C06M, C35M, C36M, and C37M that are neutron irradiated to 1.8 displacements per atom (dpa) at 357°C. Grain boundary Cr enrichment and Al depletion are observed in all irradiated alloys that span the 10-13 wt.% Cr and 5-6 wt.% Al composition space. Fe will either enrich or deplete at grain boundaries to balance the grain boundary composition. The Cr enrichment is attributed to interstitial diffusion, consistent with that in body centric cubic 9-12 wt.% Cr steels. The depletion of Al occurs through the same mechanisms as α−α′ phase partitioning previously observed in FeCrAl alloys. This study underscores the need for FeCrAl alloy design to consider RIS implications on corrosion and oxidation susceptibility.

Deformation dynamics of a neutron-irradiated aluminum alloy: An in situ synchrotron tomography study

To reveal the effects of long-term neutron irradiation on the mechanical behavior of nuclear materials, in situ quasi-static uniaxial tensile tests are conducted on an LT21 aluminum (Al) alloy from a decommissioned research reactor. Scanning/Transmission electron microscopy (SEM/TEM), and micro CT are first applied to characterize the microstructures of LT21 Al alloys aged naturally and neutron-irradiated for 30 years. In situ synchrotron micro computed tomography (CT) is adopted to characterize the deformation and damage dynamics of this LT21 Al. A new particle tracking analysis technique is proposed to quantify the displacement/strain fields and microstructural evolution (e.g., particle movement and pore growth) in the irradiated sample. Long-term irradiation induces considerable microstructural changes in the LT21 Al alloy, including the precipitation/aggregation of micron-sized Si particles and nanoscale Mg2Si particles. In addition, the size of pores and particles in the irradiated material appear considerably larger than that in the unirradiated material. During tension, the alloy undergoes elastic-plastic deformation followed by shear-dominated necking failure. The porosity and pore size exhibits an overall increase with increasing loading. Formation of new pores occurs in two modes, formation at the particle-matrix interfaces and random formation across the sample. For mode one, pores tend to nucleate at the top and bottom ends of a particle (relative to the loading direction). Formation of new pores and growth of initial and newly-nucleated pores occur simultaneously and contributes approximately equally to damage accumulation in the irradiated LT21 Al alloy before necking occurs. The deformation dynamics deepens our understanding of the aging of nuclear materials.

High Throughput Studies on Irradiated High Entropy Alloys

High Throughput Studies on Irradiated High Entropy Alloys

Towards Optimized Characterization of Dislocation Loops in Irradiated FCC Alloys Using On-Zone STEM Techniques

Towards Optimized Characterization of Dislocation Loops in Irradiated FCC Alloys Using On-Zone STEM Techniques

Emulation of neutron-irradiated microstructure of austenitic 21Cr32Ni model alloy using dual-ion irradiation

In this study, the capability of heavy-ion irradiation to emulate neutron irradiation was demonstrated on an austenitic 21Cr32Ni type ternary model alloy. The model alloy used in this study is chemically analogous but compositionally simpler than of alloy 800H, which is a candidate austenitic Ni alloy which has been proposed for use in Generation IV reactors.The microstructure of the 21Cr32Ni model alloy irradiated in the BOR-60 fast reactor to 17.1 dpa and 35 dpa at ∼380 °C was characterized using transmission electron microscopy (TEM). The 17.1 dpa BOR-60 irradiated microstructure was then compared with the microstructure of the same material developed under dual-ion (DI) irradiation using various He/dpa ratios between 0.1 and 16.6 appm He/dpa in the temperature range of 430 °C-500 °C. The results showed that both neutron and DI irradiation of 21Cr32Ni model alloy produced dislocations in the form of a dislocation network as well as {111}-type faulted dislocation loops, cavities, and radiation-induced Ni enrichment at radiation-induced sinks. When the dose and the He/dpa ratio were kept similar to those in neutron irradiation, DI irradiation of the 21Cr32Ni model alloy at 460 °C resulted in over-nucleation of small cavities and in a high density of faulted dislocation loops compared to those observed in the fast-neutron irradiated alloy of the same heat irradiated at ∼380 °C. The optimal condition for reproducing the neutron-irradiated microstructure was DI irradiation at 460 °C and 0.1 appm He/dpa. In that case, the faulted loop and cavity size distributions in the BOR-60 irradiated 21Cr32Ni model alloy samples closely matched with those measured in the DI irradiated 21Cr32Ni model alloy sample. The fact that the He/dpa is an order of magnitude smaller than the helium generation rate for fast neutron irradiation, stops over nucleation and allows for the development of a similar microstructure as for neutron irradiation.

The effect of helium on cavity swelling in dual-ion irradiated Fe and Fe-10Cr ferritic alloys

Ferritic-martensitic (FM) steels for in-vessel components in proposed fusion reactors are expected to suffer from high levels of displacement damage and helium (He) generation by neutron transmutation. However, a thorough understanding of the He synergistic effects on the cavity swelling in FM steels is still not well established. To gain fundamental insights into the He effect on cavity swelling, high purity Fe and Fe-10 wt.% Cr ferritic model alloys were irradiated with 8 MeV Ni ions and co-implanted He ions at 400 to 550 °C up to 30 displacements per atom (dpa) with He implantation rates of 0.1, 10 and 50 appm He/dpa. The current study focuses on the 50 appm He/dpa, 500 °C behavior vs. 0.1 and 10 appm He/dpa. Irradiation-induced defects, including cavities, dislocation loops, and dislocation networks were characterized using transmission electron microscopy (TEM). In the grain interior, a bimodal cavity size distribution was observed in the 10 and 50 appm He/dpa samples, but not for 0.1 appm He/dpa. Cavity swelling was maximized at intermediate He implantation rates of ∼10 appm He/dpa for both ion-irradiated Fe and Fe-10Cr alloys. The cavity swelling behavior as a function of He implantation rate appears to be controlled by the He/dpa-dependent variation of cavity sink strengths. Treating small bubbles as biased sinks for interstitial absorption can significantly increase the ratio of biased to unbiased sink strengths (Q) and results in maximized cavity swelling for a Q ratio close to one.

Deep learning object detection in materials science: Current state and future directions

Deep learning-based object detection models have recently found widespread use in materials science, with rapid progress made in just the past two years. Scanning and tunneling electron microscopy methods are among the most important and widely used characterization techniques for understanding fundamental materials structure–property-performance linkages from the micron to atomic scale. Dramatic increases in dataset size and complexity from modern electron microscopy instruments have necessitated the development and use of automated methods of extracting pertinent features of images. Here, the use of object detection in materials science, with a focus on the analysis of features in electron microscopy images, is reviewed. Key findings and limitations of recent seminal studies using object detection to characterize and quantify defects in irradiated metal alloys, segment and analyze micro and nanoparticles, find individual atoms at the nanoscale, and detect and track objects from in situ video are reviewed. Opportunities and challenges presently facing the materials community are highlighted, where discussion of best practices for model assessment and applicability are presented, along with the potential of improved model training with synthetic data. This review concludes with offering more speculative, forward-looking thoughts on the potential of the broader materials community to construct a living ecosystem integrating community-consensus curated data and validated models as tools to best inform application of object detection and segmentation models to specific materials domains.

An atom probe study on the Fe distribution in Zr-based alloys with different Fe content under high fluence neutron irradiation

In the present study, atom probe tomography was used to investigate the relationship between the distribution of Fe and other alloying elements and irradiation defects in irradiated zirconium alloys. The alloying element Fe, which is effective in increasing the corrosion resistance of fuel cladding materials, has low solubility in the Zr matrix phase and forms intermetallic precipitates during fabrication, but the distribution of Fe changes due to its dissolution into the matrix phase by neutron irradiation. The Fe atom map revealed that the dissolved Fe concentrated in the 〈a〉 dislocation loops, which is one of the irradiation defects in the Zr lattice, and formed spheroidal and ring-shaped Fe nanoclusters in the matrix phase. The ring-shaped Fe nanoclusters were widely observed in the matrix of the highly irradiated sample with high Fe content, and the distribution of dissolved Fe was affected by the Fe content and the neutron fluence. A stripe pattern of Fe distribution with these Fe nanoclusters lined up on the basal plane appeared after high fluence irradiation, and the stripe pattern was clear in the sample with higher Fe content. The dissolved Fe was retained in the matrix phase as nanoclusters, which could contribute to the corrosion resistance as well as the mechanism by Fe in the precipitates. Regarding the distribution of other alloying elements, Ni was observed in the same position as the spheroidal and ring-shaped Fe nanoclusters in the matrix phase. On the other hand, Cr was only observed as spheroidal Fe-Cr nanoclusters formed around the precipitates.

A data science approach for analysis and reconstruction of spinodal-like composition fields in irradiated FeCrAl alloys

A statistical method for the analysis of continuously distributed data representative of composition fluctuations in irradiated FeCrAl alloys acquired using Energy Dispersive X-ray Spectroscopy (EDS) method is presented. Using probability distribution functions, direct and cross-covariances between the elemental compositions, the effects of alloy composition and irradiation dose were investigated on the spatial distribution and length scale of composition fluctuations at the nanoscale. It was observed that, for neutron-irradiated FeCrAl alloys, the distribution of Fe and Cr followed a left-skewed and right-skewed distribution, respectively for all (average) alloy compositions and irradiation doses. The analysis also revealed enhanced spatial gradients in the elemental compositions at higher irradiation dose. Direct and cross-covariance estimates of the experimental data were also utilized for reconstruction of composition data through fitting it to a parametric form of the covariance functions. Linear Model of Coregionalization was used to determine the parameters of the covariance functions. Subsequently, a spectral method was utilized for simulating a realization of the alloy compositions. Close correspondence was observed between the experimental and the reconstructed data which was analyzed using probability distribution functions and covariance functions. Composition space of the experimental and reconstructed data and dislocation velocities as a function of applied stress and line directions over the entire composition maps were also examined.

Towards Quantitative Inference of Nanoscale Defects in Irradiated Metals and Alloys

Quantifying the population of nanoscale defects that are formed in metals and alloys exposed to extreme radiation environments remains a pressing challenge in materials science. These defects both fundamentally alter material properties and seed long-timescale performance degradation, which often limits the lifespan of engineering systems. Unlike ceramic and semiconducting materials, these defects in metals and alloys are not spectroscopically active, forcing characterization to rely on indirect measurements from which the distribution of nanoscale defects may be inferred. In this mini-review, different experimental methodologies which have been employed for defect inference are highlighted to capture the current state of the art. Future directions in this area are proposed, which, by combining data streams from multiple and complementary characterization methods in concert with multi-scale modeling and simulation, will enable the ultimate goal of quantifying the full spectrum of defects in irradiated metals and alloys.

Performance and limitations of deep learning semantic segmentation of multiple defects in transmission electron micrographs

Transmission electron microscopy (TEM) is a popular method for characterizing and quantifying defects in materials. Analyzing digitized TEM images is typically done manually, which is a time-consuming and potentially error-prone task that is not scalable to large dataset sizes, motivating development of automated methods for quantifying and analyzing defects in TEM images. In this work, we perform semantic segmentation of multiple defect types in electron microscopy images of irradiated FeCrAl alloys using a deep learning mask regional convolutional neural network (Mask R-CNN) model. We evaluate the performance of the model based on distributions of defect shapes, sizes, and areal densities relevant to informing physical modeling and understanding irradiated Fe-based materials properties. To better understand the performance and present limitations of the model, we provide examples of useful evaluation tests, which include a suite of random splits and dataset-size-dependent and domain-targeted cross-validation tests, exposing potential weak points in the model applicability domain. Our model predicts the expected irradiation-induced material hardening to within 10–20 MPa (about 10% of total hardening), on par with experimental error. Finally, we discuss the first phase of an effort to provide an easy-to-use, open-source object detection tool to the broader community for identifying defects in new images.

Helium interaction with solutes and impurities in neutron-irradiated nanostructured ferritic alloys: A first principles study

Density functional theory (DFT) calculations are performed to explore the binding between He and alloying solutes, impurities, and transmutation products expected in neutron irradiated nanostructured ferritic alloys (NFAs), here 14YWT is taken as an example. Elements that exhibit significant binding (attraction) with an interstitial He are: Y (binding energy = 0.46 eV), Mg (0.32), O (0.33), Ti (0.16), and C (0.15). Those that provide significant binding to a substitutional He are: O (1.44), Y (1.24), N (0.73), H (0.56), Mg (0.52), Ti (0.34), Si (0.34), C (0.33), Al (0.32), Ni (0.26), Ta (0.23), and Mn (0.16). The presence of these elements in Fe matrix could reduce the transport of He towards oxide particles, dislocations, and internal boundaries, and could promote He bubble nucleation in the matrix. For convenience, we compile existing binding energy data of He with Hen and HenV (He-vacancy) clusters. Dissociation pathway analysis reveals that, in general, the most likely dissociation of a HenV cluster is by a sequential emission of individual He atoms. Furthermore, larger bubbles are more prone to dissociation than smaller ones. In addition, we estimate the binding energy (segregation energy) of He in bulk Y2Ti2O7 (YTO) single crystal, YTO/Fe interface, and YTO particle embedded in Fe, with respect to interstitial He in Fe, from existing formation energies of He in these structures. We also compile available data of He binding with Fe self-interstitial atom (SIA), SIA clusters, and edge and screw dislocations. Note that given the absence of DFT data, the binding with SIA clusters and dislocations are gathered from simulations with empirical potentials. The data presented in this paper is important to inform multiscale simulations of He bubble accumulation.

Influence of thermomechanical exposure on the structure of hydrides in irradiated E110 alloy cladding pipes under the conditions of long-term dry storage of spent nuclear fuel

The penetration of atomic hydrogen into the cladding material of fuel elements of WWER-1000 reactors due to interaction with the coolant during operation can subsequently significantly reduce their plasticity characteristics with a decrease in temperature during long-term dry storage of spent nuclear fuel (SNF) due to the formation of brittle hydrides. The morphology of hydrides influenced by the hydrogen content, storage temperature and circumferential stresses plays a decisive role in the embrittlement of the fuel cladding material. Associated radial hydrides are of particular danger; they constitute the most favorable path for crack propagation.In the present work, thermomechanical tests of irradiated fuel claddings samples made of the E110 alloy were carried out, simulating normal and emergency conditions of long-term dry storage. It was shown that under the conditions considered, the formation of a significant amount of radially oriented hydrides was observed, leading to degradation of mechanical properties (embrittlement) fuel cladding.

Impact of nano-oxides and injected gas on swelling and hardening of 18Cr10NiTi stainless steel during ion irradiation

The radiation performance of 18Cr10NiTi-ODS steel with the addition of Y2O3-ZrO2 nano-oxides was compared with that of non-ODS 18Cr10NiTi austenitic steel in terms of radiation-induced hardening and cavity swelling. TEM observations were performed to evaluate the effect of grain refinement and nano-sized oxide precipitates on microstructural changes and radiation tolerance in specimens exposed to 1.8 MeV Cr3+ or 1.4 MeV Ar+ irradiations over a wide range of temperatures. Formation of homogenously distributed voids was observed in both alloys upon Cr3+ irradiation but the ODS steel exhibited a considerably broader temperature range of void formation and lower overall swelling. Cavity formation in steels irradiated with Ar+ showed a strong dependence on Ar/dpa ratio. Argon addition was found to enhance the nucleation of cavities, which act as point defects sinks that reduce void swelling. The largest swelling resistance was observed in the ODS steel due to the combined effect of mechanical alloying and Ar gas co-injection. The hardening behavior was investigated in both non-irradiated and Ar+ irradiated samples at room temperature and elevated temperatures by means of nano-indentation. Along with the strengthening effect of radiation-induced dislocations, gas-filled nano-cavities strongly contribute to the hardening of irradiated alloys with a tendency to increase the barrier strength of nano-cavities with decreasing cavity size. The ODS variant was found to be somewhat less susceptible to radiation hardening compared to non-ODS 18Cr10NiTi steel.

Void swelling of conventional and composition engineered HT9 alloys after high-dose self-ion irradiation

Ferritic/martensitic (F/M) steels are being considered as potential structural materials for next generation nuclear reactors, and variants of the alloy HT9 are some of the most promising candidates. In this study, two conventional and two composition engineered HT9 alloys were irradiated using 3.5 MeV Fe2+ up to 600 peak displacement-per-atom (dpa) at 450 ℃. Void swelling and microstructure evolution were characterized for each alloy and compared. The two conventional HT9 alloys (INL and ACO3) showed similar void swelling behavior due to their similar elemental composition and processing conditions. The INL HT9 exhibited a maximum of 2.4% swelling and the ACO3 HT9 showed a maximum of 2.8% swelling at 342 and 393 average local dpa, respectively. On the other hand, the two-composition engineered HT9 alloys with varying N contents (10 ppm for low N and 440 ppm for high N) showed disparate swelling behavior. The low N HT9 exhibited a maximum of 4.6% swelling, while the high N HT9 showed a maximum of 0.7% swelling at 342 average local dpa. Changes in the N content also affected Ni/Si rich G-phase formation. The low N HT9 showed a larger size and lower density of G-phase precipitates compared with the high N HT9 after 600 peak dpa irradiation. This study compares the void swelling behavior of the ion irradiated four current HT9 alloys to extremely high doses, with the void swelling data from neutron irradiated HT9 alloys. The comparison lends critical insights into how well these current alloys can withstand high neutron fluxes in future reactors, especially since the low N and high N HT9 alloys have never been exposed to such high doses before.

Quantitative characterization of frank loops and their effects on the plastic degradation in heavy ion irradiated alloy 800H

Alloy 800H has recently received significant attention owing to its potential applications in molten salt reactors. However, its irradiation tolerance and plastic degradation after irradiation are not well understood. In this study, Alloy 800H was irradiated by 3 MeV Cu+ ions with irradiation damage up to 10 dpa. The microstructure changes were characterized using two Rel-rods cases and weak beam dark field technology by performing transmission electron microscopy. The plastic mechanical properties before and after the irradiation were extracted from P-h curves derived by performing nanoindentation at loading rates of 0.05, 0.1, and 0.5 nm/s. The microscopy studies demonstrate that the characterization and evolution of the two variations of Frank loops are distinct and the 13⟨1‾11⟩ Frank loops firstly nucleate and coarsening. The nanoindentation results demonstrate that the measured yield stress increases with the increasing irradiation damage and decreasing loading rate. The good agreement on yield stress between the calculated and measured values suggests that using the characteristics of two variations of Frank loops to calculate the contribution of yield stress is appropriate. In addition, the decreasing measured values with increasing loading rate are attributed to the increased geometrically necessary dislocations, which are correlated with the indent size effect.

Irradiation and thermal effects on the mechanical properties and solute cluster evolution of Fe-Cu alloy

Fe-1.3at.% Cu alloys were irradiated at 563 K and 773 K to explore the irradiation and thermal effects on the mechanical properties and solute cluster evolution of Fe-Cu alloy. Nanoindentation and atom probe tomography were performed to characterize the hardness and distribution of the solute atoms. The results show that hardness of the alloy increases after irradiation at both temperatures and higher hardness increment is observed at 773 K. Cu clusters with a high number density are formed after irradiation. The volume fraction of the clusters increases from about 0.70% at 563 K to 2.80% at 773 K. These clusters contribute to the hardening of the irradiated alloys. Upon comparing the size and number density of these clusters at different temperatures with different doses of 0, 0.018 and 0.18 dpa, it’s found that although both irradiation and thermal effects enhance the precipitation of Cu atoms from the matrix, they have an opposite effect on the evolution of Cu clusters: thermal effect enhances the growth of stable Cu clusters, whereas irradiation primarily promotes the nucleation of the Cu clusters and decomposes the larger Cu clusters.

Enhancing the phase stability of TiNi intermetallic compound via nanocrystallization in an irradiated multicomponent vanadium alloy

Intermetallic compounds often have a low radiation tolerance due to the low recombination rate of radiation-induced defects. In the present work, we designed a novel multicomponent vanadium-based alloy (MVA), V34Ti25Cr10Ni30Pd1, containing a micron-scale TiNi matrix phase with VCr nanoprecipitates (NPs) and a micron-scale VCr matrix phase with TiNi NPs. The MVA was irradiated with 6 MeV Ti3+ ions with a radiation dose of 5×1015ions/cm2 at room temperature. Results indicated that the micron-scale intermetallic TiNi matrix along with VCr NPs inside both became amorphous, while the micron-scale VCr matrix including numerous intermetallic TiNi NPs both exhibited a high structural stability after ion irradiation. The intermetallic TiNi matrix becomes amorphous due to the accumulation of radiation-induced defects, and the intermetallic TiNi NPs in VCr matrix have a high stability of crystallographic structure due to high-density interfaces between NPs and matrix. These results indicate that the phase stability of TiNi intermetallic compound is increased after nanocrystallization. Besides, the discrepancy of two matrix phases including precipitates after ion irradiation, and the underlying mechanisms are discussed in detail in this work. This work gives a guidance for designing new vanadium alloys and intermetallic compounds with enhanced structural stability under ion irradiation.

Influence of proton irradiation on the microstructure and mechanical properties of Nb-1Zr-0.1C alloy

• Effect of proton irradiation on Nb-1Zr-0.1C alloy proposed for CHTR. • XRD line profile analyses of the data collected using synchrotron source. • Prediction of dislocation loop formation with XRDLPA and supported by TEM analysis. • Microstructure-mechanical property correlation by tensile and nanoindentation test. • Comparison of microstructure and mechanical properties with proton irradiated pure Nb . The microstructural evolution and corresponding changes in mechanical properties of proton irradiated Nb-1Zr-0.1C alloy have been studied as a function of irradiation dose. Different XRD line profile analyses (XRDLPA) have been carried out using synchrotron XRD data to evaluate the microstructural parameters. It is observed that coherent domain size decreases with an increasing microstrain within the domain as a function of dose. The dislocation density also increases and shows saturation at the highest dose. The Wilkens arrangement parameter decreases as a function of dose indicating the formation of correlated dislocations in the alloy matrix. Transmission electron microscopy (TEM) analysis confirms the presence of dislocation loops in the highest dose sample supporting the findings of XRDLPA. The strength and ductility of unirradiated and all irradiated samples have been evaluated as a function of dose. It is observed that the ductility reduces continuously along with increasing yield strength (YS) and ultimate tensile strength (UTS) as a function of dose. Nanoindentation was also carried out to measure the change in hardness of the alloy with dose. It is observed that the value of the nanohardness increases continuously from 1.74 GPa for the unirradiated sample to 2.43 GPa in the highest dose irradiated sample. Systematic changes are observed on the morphology of fracture surface as a function of dose. Signature of ductile failure is observed in the unirradiated sample whereas brittle failure is prominent in the irradiated samples with higher dose. The change in microstructure in terms of dislocation density is corroborated with the change in mechanical properties in terms of YS of the irradiated alloy. Contradistinction of the findings of Nb-1Zr-0.1C with those of pure Nb contemplated the role of the alloying additions, especially carbon, in governing the irradiation behaviour of the alloy.

Effect of Structural and Phase Changes under Relativistic Electron Pulsed Beam Irradiation on the Aluminum Alloys Micro-hardness

The paper studies the distinctive features of micro-hardness value changes in the zone of industrial aluminum alloy 1933 and alloy 1380 irradiated by the relativistic electron beam. The surface layer was modified under the relativistic electron beam injected along with the equal energy parameters. However, we have to claim that some physical and technological properties of the irradiated alloys layer came with some differences. The modified layer micro-hardness increased over 30% in 1933 aluminum alloy and decreased by 10% in 1380 aluminum alloy. The mechanisms affecting the metal material strengthening transformation after a pulsed electron beam application are analyzed. Thus it was established that one of the core impacts to increase the micro-hardness of 1933 aluminum alloy surface layer was fine MgO impurities being absent in the initial alloy and caused by the irradiation, whilst the micro-hardness of the irradiated layer of the 1380 aluminum alloy decreases due to the dissolution during irradiation of the strengthening phases, which were identified in the initial state.