Single crystals of transition metal carbides from group IV, TiC1-x and ZrC1-x, have been irradiated at room temperature (RT) with 1.2 MeV gold ions for various fluences in the range 2 x 10(14)-3 x 10(16) ions/cm(2) and polycrystals for fluences between 2 x 10(13) and 4 x 10(15) ions/cm(2). The irradiated samples were characterized by micro Raman spectroscopy. For this purpose, the evolution of main parameters of Raman spectra for both types of samples (band positions, shifts, and intensities, and optical over acoustical band area ratios) versus ion fluence are reported, and discussed. All acoustic and optical bands increase and broaden with fluence. Yet no amorphization is achieved under the highest fluence for both carbides. From the lowest fluence up to 10(15) ions/cm(2), point defects like interstitials and vacancies are created. The increasing number of carbon vacancies involves a local variation in stoichiometry accompanied by carbon release. For fluence above 10(15) ions/cm(2), extended defects like dislocation loops appear, as seen by TEM observations.

Transition-metal ultra-high temperature ceramics are promising materials for nuclear structural applications. However, an understanding of their response to high-temperature irradiation and helium is vastly limited. This paper presents a study of helium effects in zirconium carbide (ZrC) by performing room temperature 3 MeV He-3(+) ion irradiations up to 5 x 10(20) ions m(-2) (similar to 1.8 at.% at peak) and high temperature annealing (1273-1873 K), coupled with state-of-art characterization using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and nuclear reaction analysis (NRA). We reveal that ZrC is susceptible to irradiation damage in terms of helium bubble formation. After annealing at 1373 K, tiny bubbles (1-2 nm) formed aligned clusters which were highly over-pressurized, producing strain contrast in TEM. At 1773 K, significant bubble growth occurred. Additionally, at 1773 K, a combined TEM/SEM analysis revealed dramatic matrix damage due to helium-induced surface blistering. Underneath blister caps, the microstructure evolved into ultra-fine nano-scale grains similar to high burn-up structures observed in nuclear fuels, but consisting of numerous nano-cracks. We hypothesize that such structures are formed due to high gas pressure build-up and its subsequent release. This phenomenon initiated at the grain boundaries. Blister top surface consisted of inter-granular and trans granular cracks. NRA depth profiling revealed that helium was present as double peaks with major portion lying at the end-of-the-range (EOR) and the rest as TEM invisible clusters in a shoulder extending to the surface. ZrC started releasing helium after 1373 K. Helium release increased significantly at higher temperatures, with majority helium loss occurring from EOR rather than from near-surface regions. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Bare and Al2O3-coated austenitic steel samples are exposed to lead-fast-reactor\relevant corrosive conditions. Selective leaching of Ni, Mn and Cr is observed in bare samples exposed to high temperature stagnant lead (550 degrees C, 10(-8) wt.% oxygen, 1000 and 4000 h). By contrast, corrosion is not observed in either pristine (4000 h) or irradiated (1000 h) coated samples. Further characterization and testing methods include SEM, TEM, STEM, EDS, cyclic nanoimpact, microindentation, scratch, and thermal cycling. Overall, the results show that the coatings retain structural integrity under the conditions investigated, which is a crucial prerogative for corrosion protection with ceramic coatings.

The Reduced Activation Ferritic/Martensitic (RAFM) steels are promising structural materials for the first wall and blanket components of future fusion reactors. To obtain further insight into the temperature dependence of helium effects induced by 14 MeV energy neutroris under fusion like conditions, EUROFER97 was exposed to He+/Fe3+ dual-beam ion irradiation at the JANNUS laboratory at Saclay. The implantation was carried out at temperatures of 330 degrees C, 400 degrees C and 500 degrees C and induced a damage and helium concentration up to 26 dpa and 450 appm He, respectively. TEM microstructure analysis indicates a spatially homogeneous distribution of helium bubbles at 330 degrees C and 400 degrees C whereas a coexistence of homogeneous and heterogeneous nucleation of bubbles is found at 500 degrees C. An increasing mean bubble diameter and decreasing concentration of bubbles with rising irradiation temperature, as predicted by numerical results of a kinetic rate model for diffusion governed honlogeneous nucleation of helium bubbles, are mostly confirmed by the irradiation experiment. Furthermore, within the rate model two approaches for the determination of the thermodynamic properties of helium filled voids in alpha-iron are applied. With respect to the final bubble size distribution, the commonly used surface energy of a void in the iron matrix is compared to the "variable gap model" of [1], J. Nucl. Mater. 418 (2011), which includes additionally the interaction between the helium atoms themselves, the energy at the helium -iron interface and the elastic deformation of the iron matrix. (C) 2016 Published by Elsevier B.V.

The goal of this study was to understand the microstructural evolution of two industrial titanium alloys (grade 2 and 5) under irradiation in order to derive information for potential application in nuclear industry especially for internals in nuclear reactors. Ion irradiation conditions were chosen to obtain a homogeneous damage profile of a few dpa over 500 nm depth in six hours (corresponding to one irradiation day). The influence of both the dose and temperature was taken into account. A special attention paid to counting defects revealed an evolution with the dose, the temperature and the nature of the material. After 0.6 and 3 dpa irradiations at 450°C, using the JANNuS-Saclay facility, TEM characterization showed that a thin precipitation of rich vanadium β-phase occured in the a-phase of Ti6-4, in addition to the loops present in both materials.

AbstractAmong ion‐beam‐based analytical methods, the direct observation of nuclear reactions induced by highly energetic (MeV regime) charged particles is dedicated to the quantitative determination of volume distributions of light elements fromZ= 1 (H) toZ= 41 (Ga) in the near surface region of solids. In most cases, discrimination between their isotopes is enabled up to37Cl. The incident ions are generally protons, deuterons, helium‐3, or helium‐4 ions. Nuclear reactions induced by heavier ions are sometimes also used, mostly for hydrogen depth profiling. All these reactions are characterized by the prompt emission of charged particles (protons or helium‐4 ions) and/or γ‐rays. Nuclear reaction analysis (NRA), performed in ion millibeam or microbeam modes, is an efficient complement to charged particle‐induced X‐ray emission, Rutherford backscattering spectrometry, and elastic recoil detection methods. Its applications are all intended for either absolute quantification or tracing experiments. They cover a broad panorama from life sciences to cultural heritage artifacts, including metallurgy, Earth sciences, nanotechnology, and material science.

The lack of suitable materials solutions stands as a major challenge for the development of advanced nuclear systems. Most issues are related to the simultaneous action of high temperatures, corrosive environments and radiation damage. Oxide nanoceramics are a promising class of materials which may benefit from the radiation tolerance of nanomaterials and the chemical compatibility of ceramics with many highly corrosive environments. Here, using thin films as a model system, we provide new insights into the radiation tolerance of oxide nanoceramics exposed to increasing damage levels at 600 °C – namely 20, 40 and 150 displacements per atom. Specifically, we investigate the evolution of the structural features, the mechanical properties, and the response to impact loading of Al2O3 thin films. Initially, the thin films contain a homogeneous dispersion of nanocrystals in an amorphous matrix. Irradiation induces crystallization of the amorphous phase, followed by grain growth. Crystallization brings along an enhancement of hardness, while grain growth induces softening according to the Hall-Petch effect. During grain growth, the excess mechanical energy is dissipated by twinning. The main energy dissipation mechanisms available upon impact loading are lattice plasticity and localized amorphization. These mechanisms are available in the irradiated material, but not in the as-deposited films.

In this paper, the behavior of helium and its influence on the microstructure in polycrystalline titanium nitride (TiN) is studied by ion implantation technique, coupled with post-implantation annealing experiments between 1273 and 1873 K. The samples were implanted at room temperature with helium up to similar to 2.2, 0.25 and 0.07 at. % at the implantation peak, respectively. Helium induced bubble microstructure was characterized using transmission electron microscopy (TEM) which revealed the effect of annealing temperature and helium concentration on the evolution of the bubbles in the material. TEM analysis also revealed that no amorphisation occurred up to the maximum dose level of 0.8 dpa at room temperature, corresponding to the highest implantation level. The technique of nuclear depth profiling using nuclear reaction analysis (NRA) revealed the helium diffusion and retention behavior in the material at different annealing temperatures and helium concentration levels. A sharp increase in helium loss from TiN occurred after annealing beyond 1373 K for the highest helium level, whereas no loss occurred for the lowest implanted helium level. The effective activation energies of helium diffusion and release were estimated utilizing Fick's law of diffusion and 1st order kinetic law, respectively. A novel method of estimating pressure inside bubbles is discussed by utilizing the high-density equation of state, incorporating the experimentally determined helium density, deduced from coupling the result of helium concentration measurement from NRA and vacancy concentration measurement from the experimentally determined size and number density of bubbles from TEM. These results reveal that such kind of calculation technique can be utilized for bubbles formed at higher annealing temperatures. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

{110}-oriented yttria-stabilized zirconia single crystals have been implanted with low-energy C ions in an axial direction, at room temperature and at 550 °C. Room temperature ion implantation generated a damage layer that contains the expected dislocation loop clusters. Strikingly, the high temperature implantation produced zirconium oxycarbide nanoparticles (ZrCxOy) at a shallow depth in the yttria-stabilized cubic zirconia crystal, with a diameter in the range of 4–10 nm. Moreover, in the high concentration region of implanted C ions, between 100 and 150 nm below the surface, a number of large precipitates, up to 20 nm, were observed.

Single and dual-beam ion irradiations of silicon carbide (SiC) were performed to study possible Synergetic effects between Nuclear (S-n) and Electronic (S-e) Energy Losses. Results obtained combining Rutherford backscattering in channeling conditions, Raman spectroscopy, and transmission electron microscopy techniques show that dual-beam irradiation of SiC induces a dramatic change in the final sample microstructure with a substantial decrease of radiation damage as compared to single-beam irradiation. Actually, a defective layer containing dislocations is formed upon dual-beam irradiation (S-n&S-e), whereas single low-energy irradiation (S-n alone) or even sequential (S-n + S-e) irradiations lead to full amorphization. The healing process is ascribed to the electronic excitation arising from the electronic energy loss of swift ions. These results shed new light on the long-standing puzzling problem of the existence of a possible synergy between S-n and Se in ion-irradiation experiments. This work is interesting for both fundamental understanding of the ion-solid interactions and technological applications in the nuclear industry where recovery S-n/S-e effects may preserve the integrity of nuclear devices. (C) 2015 AIP Publishing LLC.

The response of zirconium carbide to heavy-ion irradiation at room temperature has been studied by Xray diffraction, ion channeling and transmission electron microscopy. Below 5 x 10(14) cm(-2), we observe a build-up of elastic strain with increasing fluences. At this threshold fluence the strain is released and important dechanneling appears as well as visible TEM damage. With increasing fluence, this damage is found to spread in the material deeper than the depth of direct damaging by the ion beam. These experimental observations are reproduced and explained by Density Functional Theory informed Rate Equation Cluster Dynamics simulations. Simulations show that the response of ZrC upon ion-irradiation is driven by the diffusion and clustering of interstitials. The two-step evolution seen in experiments stems from the growth of interstitial clusters with a concomitant starvation of the smallest clusters induced by the continuous accumulation of vacancies. The damaging of the material beyond the range of primary damage is driven by diffusion of interstitials. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The Oxide Dispersion Strengthened (ODS) materials are potential candidates as cladding tubes for Sodium-cooled Fast Reactors. The nano-oxides are finely dispersed within the grains and confer excellent mechanical properties to these alloys. Hence, assessing nano-particle stability under irradiation remains crucial to guarantee safe use of these materials. Although neutron irradiation remains a binding and challenging experimental study to conduct, difficulties can be overcome by ion beam processing. Ion beam processing of the ODS material allows to identify the radiation-induced Ostwald ripening as the mechanism governing the nano-particle response under irradiation. The result is the increase in size and a decrease in density of the finely dispersed Y_2Ti_2O_7 nano-particles. Under neutron irradiation, radiation-induced Ostwald ripening appears to be less effective since a slight growth of nano-particles is observed. Further, our approach shows that nanoparticle growth kinetics should scale as φ^1/3, φ being the radiation flux. This suggests that the low irradiation flux is at the origin of the slower growth kinetics of the neutron irradiated particles. Both neutron and ion irradiation induce a modification of the nanoparticles/matrix interfaces which are generally flat and sharp prior to irradiation and present steps after irradiation. This could alter the nano-particle coarsening during irradiation.

RAFM steels such as Eurofer-97 and Eurofer-ODS are potential structural materials for future fusion reactors. In order to study their resistance to the high energy neutrons they will be subjected to in this context, we have irradiated these materials in single-, dual- and triple-beam mode to 26 dpa at 400 degrees C. In single-beam mode (Fe ions only), both materials resist swelling but dislocation loops form. For dual- (Fe and He ions) and triple-beam (Fe, He and H) modes, the same dislocation loop microstructure is observed as for the single-beam mode, but small cavities form, aided by the presence of gases. Despite the formation of cavities, swelling is very low for the present conditions. The influence of ODS particles on swelling is briefly discussed. (C) 2015 Elsevier B.V. All rights reserved.

ODS materials constitute a new promising class of structural materials for advanced fission and fusion energy application. These Fe–Cr based ferritic steels contain ultra-high density of dispersion-strengthening nanoclusters conferring excellent mechanical properties to the alloy. Hence, guarantee the nanocluster stability under irradiation remain a critical issue. Nanoclusters are non-equilibrium multicomponent compounds (YTiCrO) forming through a complex nucleation pathway during the elaboration process. In this paper, it is proposed to observe the response of these nanoclusters when the system is placed far from equilibrium by means of ion beam. The results indicate that the Y, Ti, O and Cr atoms self-organized so that nanoclusters coarsened but maintain their non-equilibrium chemical composition. It is discussed that the radiation-sustained nanocluster metastability emerges from cooperative effects: radiation-induced Ostwald ripening, permanent creation of vacancies in the clusters, and fast Cr diffusion mediated by interstitials.

JANNUS (Joint Accelerators for Nanosciences and Nuclear Simulation), the unique triple beam facility in Europe, offers the possibility to produce three ion beams simultaneously for nuclear recoil damage and implantation of a large array of ions for well-controlled modeling-oriented experiments. The first triple beam irradiation was performed in March 2010. Along with irradiation developments, continuous efforts have been made to implement ex situ and in situ characterization tools. In this study, we set out the present status of the JANNUS facility of the Saclay site. We focus on the instrumentation used for conducting multi-ion beam irradiations and implantations as well as for characterizing bombarded samples. On-line control of irradiation parameters, in situ modification monitoring using Raman spectroscopy or ion beam induced luminescence, and ex situ characterization by ion beam surface analysis [Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), and elastic recoil detection analysis (ERDA)] of implanted samples are detailed. Some examples of single, dual, and triple beam irradiation configurations are presented. Access to the facility is provided by the French network EMIR for national and international users ( http://emir.in2p3.fr/ ).

Raman spectroscopy is an efficient technique for studying the evolution of microstructure of materials under irradiation. For that purpose, a Raman spectrometer has been recently installed at the JANNUS‐Saclay platform. In this paper, we describe the new setup for in situ experiments. These in situ experiments allowed following the microstructural evolution of different materials (SiC, ZrO2 and B4C) as a function of ion fluence on a single sample (either single crystal or polycrystalline ceramics) under the same irradiation conditions. Our results show that Raman spectroscopy is a versatile non‐contact technique for studying on‐line crystalline phase changes or amorphization of irradiated iono‐covalent solids. A detailed analysis of Raman spectra is provided for the three materials (SiC, ZrO2 and B4C) investigated in this study, revealing quite different behaviors upon irradiation. Basically, Raman spectroscopy gives insight on these evolutions at the level of bonds given by specific phonon modes, in good agreement with Rutherford backscattering channeling (RBS/C), X‐ray diffraction (XRD) or transmission electron microscopy (TEM) data, which provide information at a long‐range scale. Copyright © 2015 John Wiley & Sons, Ltd.

This work is an overview of the physical approaches required for characterizing and understanding the long-term evolution of ceramics under irradiation. Because this subject is complex and has many ramifications, we have chosen to address the problem by looking at the behavior of a number of key ceramics. In the first part of this work, we present the physical mechanisms responsible for the production of primary defects, pointing out the main differences between metals, semiconductors, and insulators. In part two, we attempt to show how devoted experimental techniques can combine with transmission electron microscopy and x-ray techniques to provide a clearer picture of the long-term evolution of the microstructure of ceramics under irradiation. The last part of this work is devoted to discussing different approaches to explain and describe the long-term behavior of irradiated ceramics.

The aim of this paper is to point out and to discuss some features extracted from the study of helium migration in nuclear materials performed during the last fifteen years using ion beam analysis (IBA) measurements.The first part of this paper is devoted to a brief description of the two main IBA methods used, i. e. deuteron induced nuclear reaction for 3He depth profiling and high-energy heavy-ion induced elastic recoil detection analysis for 4He measurement.In the second part, we provide an overview of the different studies carried out on model nuclear waste matrices and model nuclear reactor structure materials in order to illustrate and discuss specific results in terms of key influence parameters in relation with thermal or radiation activated migration of helium.Finally, we show that among the key parameters we have investigated as able to influence the height of the helium migration barrier, the following can be considered as pertinent: the experimental conditions used to introduce helium (implanted ion energy and implantation fluence), the grain size of the matrix, the lattice cell volume, the Young's modulus, the ionicity degree of the chemical bond between the transition metal atom M and the non-metal atom X, and the width of the band gap. (C) 2015 Elsevier B.V. All rights reserved.