Elevated Temperature Irradiation Research Articles

HICU PIE results of neutron-irradiated lithium metatitanate pebbles

Lithium metatitanate (Li2TiO3) pebbles were irradiated with neutrons within the HICU (High neutron fluence Irradiation of pebble staCks for fUsion) experiment to investigate their material properties and tritium release behaviour in a post-irradiation examination (PIE). The irradiation temperature is the most significant influence on the material. Besides a higher irradiation temperature, a higher initial Li–6 content tends to lead to an increased tritium generation resulting in the formation of the secondary lithium depleted phase Li4Ti5O12. A pre-compaction of the pebble bed does not have an apparent influence on the material properties. Tritium is released as semi-tritiated water and semi-tritiated hydrogen (HTO and HT) and its release is enhanced at elevated irradiation temperatures.

Post-irradiation examination of commercial tantalum alloys following neutron irradiation

Post irradiation examination of two commercial tantalum alloys (based on Ta-8 %W) revealed significant irradiation hardening following neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Tensile samples of commercial Ta alloys T-111 and ASTAR-811C were irradiated to a total neutron fluence (E > 0.1 MeV) in the range (2–4)x1021 n/cm2 (0.39–0.75 dpa) at an irradiation temperature near 900 °C. Tensile testing conducted at room temperature and at 800 °C revealed significant irradiation hardening under all test conditions. Samples that were tensile tested at room temperature exhibited brittle failure, whereas ductility was maintained for elevated temperature testing. The irradiation hardening and embrittlement noted for both alloys was attributed to irradiation-induced dislocation loop formation as confirmed through scanning transmission electron microscopy analysis. Corresponding energy dispersive x-ray spectroscopy revealed radiation-induced segregation of Hf in these loop populations. This Hf enrichment is shown to result in eventual co-precipitation of elongated (Hf,O)-rich precipitates along the dislocation loops. These results show that irradiation hardening is enhanced via irradiation-enhanced precipitation at elevated irradiation temperatures. Consequently, the minimum recommended operating temperature window for Ta alloys should be increased to account for observed hardening/embrittlement at irradiation temperatures as high as 900 °C (1,173 K).

Study of high temperature mechanical properties and irradiation behavior of Zr3Al alloy by Chen's lattice inversion EAM

An embedded atomic method based on Chen's lattice inversion (CLI-EAM) was developed for the Zr3Al binary alloy. The reliability of the potential function was established through calculations of fundamental properties of the Zr3Al binary alloy, including vacancy formation energy, elastic constants, and mechanical modulus. Utilizing the CLI-EAM model, the high-temperature mechanical behavior of the Zr3Al alloy was investigated, and comparisons were made with other existing EAM models and experimental data. The outcomes manifested the high temperatures augment disorder within the alloy lattice structure, culminating in the abatement of the maximum tensile strength of Zr3Al, but could still maintain a strength of 8 GPa at 700 K. Additionally, the mechanical performance of Zr3Al subjected to elevated temperature irradiation conditions was distinctly influenced by radiation-induced structural damage. The mechanical attributes of Zr3Al endured constancy under room temperature and 5 keV irradiation, and a substantial regression in both ultimate tensile strength and elongation was evident at 700 K. Finally, molecular dynamics simulations coupled with visual analysis elucidated the reasons for the divergence in the mechanical performances of irradiated systems at different temperatures. These findings could underscore the enhanced reliability of CLI-EAM potential model in dynamic simulations and microstructural evolution studies of Zr3Al alloys.

Tough and Photo-Plastic Liquid Crystal Elastomer with a 2-Fold Dynamic Linker for Artificial Muscles.

Liquid crystal elastomers (LCEs) have been optimized by combining cross-linkers and dynamic bonds to achieve a reversible actuation behavior comparable to living skeletal muscles. In this study, one unique type of segment with 2-fold dynamic properties was introduced into LCEs, which offered not only dynamic diselenide covalent bonds for thermo-/photoplasticity but also H-bond arrays for dynamic cross-linking and mechanical robustness. Besides self-healing, self-welding, and recyclability, the LCEs were reprogrammable with elevated temperature or intensive visible light irradiation. The resultant LCEs gave an actuation blocking stress of 1.96 MPa and an elastic modulus of 14.4 MPa at 80 °C. The actuation work capacity reached 135.2 kJ m-3. When incorporating the Joule electrode or photothermal materials, the LCEs could be programmed as the electricity-driven and photothermal artificial muscles and thereby promised the application both as a biomimetic artificial hand and as an energy collector from sunlight. Thus, the 2-fold dynamic LCEs offered the pathway of enabling the reversible actuation behavior comparable to living skeletal muscles and promising applications in sustainable actuators, artificial muscles, and soft robots.

Deuterium retention in W-Cr-Y alloy: Impact of the manufacturing method and helium presence

The retention of deuterium in tungsten-chromium-yttrium alloys, W-11.4Cr-0.6Y and W-10Cr-0.5Y, was investigated by means of in-situ thermal desorption spectroscopy (TDS). The first alloy was manufactured by field-assisted sintering technology (FAST), while W-10Cr-0.5Y alloy was produced by hot isostatic pressing followed by heat treatment (HIP+HT). Both alloys were irradiated with D3+ ions (670 eV/D) and a fluence of 1021 D/m2 at temperatures of 300, 600, 900 K. In the case of W-11.4Cr-0.6Y alloy, deuterium retention was investigated during sequential irradiation with helium (3 keV) and deuterium (670 eV/D) ions at room temperature with fluences of 1019–7 × 1022 He/m2 and 1021 D/m2, respectively.The material structure has a great influence on deuterium retention, as evidenced by the significantly increased deuterium trapping in W-11.4Cr-0.6Y alloy at both room and elevated irradiation temperatures due to the presence of high-energy trapping centers compared to W-10Cr-0.5Y alloy. In both alloys, the observed amount of deuterium released during TDS was higher than in pure tungsten.The general trend of helium influence on the deuterium retention in W-11.4Cr-0.6Y alloy is very similar to bare tungsten. Namely, deuterium retention increased until helium implantation reached a fluence of 1021He/m2, and then sharply decreased when the fluence exceeded this value.

Effects of Bias and Temperature on Interface-Trap Annealing in MOS and Linear Bipolar Devices

This article reviews the effects of applied bias and temperature on Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface-trap buildup and annealing rates. Electrical and spectroscopic methods are described to estimate interface-trap densities at oxidized Si surfaces, in MOS capacitors and transistors, and in linear bipolar devices. Illustrative results provide insights into the kinetics and energetics of interface-trap annealing. Interface traps in MOS and linear bipolar devices anneal much more easily at 0 V bias than at positive or negative applied bias. Hydrogen transport and reactions play critical roles in interface-trap buildup and annealing processes. The complex interplay between H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> diffusion and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> drift is illustrated via coupled experimental and theoretical studies. Interface-trap annealing imposes significant constraints on hardness-assurance techniques. Current MOS standard tests that incorporate accelerated aging at elevated temperature at worst case, static, positive bias enable successful assessment of MOS devices in low-dose-rate environments. However, it is not similarly possible to use elevated-temperature irradiation and/or annealing at worst case, 0 V bias to predict low-dose-rate response for linear bipolar devices and ICs. Temperature-switching during irradiation appears to be a promising approach to address this issue.

Analysis of trapping sites for deuterium in W–Cr–Y SMART alloy

Deuterium (D) retention in tungsten-chromium-yttrium (W–Cr–Y) alloy depending on the irradiation fluence of 1019–5 × 1021 D/m2 at various sample temperatures in the range of 300–900 K was investigated using in-situ thermal desorption spectroscopy (TDS). The irradiation was carried out using 2 keV D3+ ions (670eV/D). An increased D retention compared to that of pure polycrystalline W and additional high-temperature peaks were observed in TDS. The de-trapping energy of 2.21 ± 0.05 eV for these traps was determined by the Kissinger method using the series of experiment with different heating rates. The total D retention dropped down at elevated irradiation temperatures and was rather small at 900 K, but has a local maximum at about 700 K.

Distinct He-induced damage evolution in nickel-based alloys irradiated at elevated temperatures

The nickel-based alloy Inconel 617 and Alloy 800H have been envisaged as the leading candidate for the higher-temperature Molten Salt Reactors (MSRs) due to their superior high-temperature properties. To evaluate their potential applications, both alloys were irradiated by He ion at 750 and 850 °C with corresponding He ion fluence. Same irradiation tests were performed on Hastelloy N alloy to study its microstructure evolution at elevated irradiation temperature, as well as being the reference alloy to reveal candidate alloys irradiation tolerance. Transmission electron microscopy (TEM) reveals the depth distribution of irradiation induced He bubbles and Frank loops. The TEM graphs and quantitative analysis shows that when irradiated at 850 °C, the formation of precipitated clusters lead to denser and boarder distribution of He bubbles in Inconel 617, while the bubble-loop complexes form and contribute to larger volume fraction of He bubbles in Hastelloy N alloy. The nanoindentation technique is used to measure their mechanical changes, and the results show that the Alloy 800H has the lowest degree of irradiation induced hardening when irradiated at 850 °C, whereas that of all alloys irradiated at 750 °C are basically similar. Further, the yield strength increment is calculated and deviations between experimental and calculated values are caused by the formation of precipitated clusters in Inconel 617 and the selection of smaller obstacle strength in Hastelloy N alloy. By comparison, the Alloy 800H demonstrates a greater potential to function as the structural material for higher-temperature MSRs due to smaller volume fraction and better resistance to irradiation induced hardening.

Layer dissolution in accumulative roll bonded bulk Zr/Nb multilayers under heavy-ion irradiation

The heavy-ion irradiation behavior of bulk zirconium-niobium multilayered composites was investigated up to large doses. Multilayers with an average individual layer thicknesses ranging between 15 and 80 nm were synthesized by accumulative roll bonding technique. The irradiation was performed with a defocused 7 MeV Zr2+ ion beam at 500 °C. The maximum dose achieved was ∼145 dpa at the depth of ∼1.5 μm from the irradiated surface. Sub-surface microstructural damage and the chemical redistribution were characterized by transmission electron microscopy and energy dispersive spectroscopy, respectively. Irrespective of the layer thicknesses, the irradiation condition caused layer instability and the extent of damage varied with the dose levels. Doses lesser than ∼60 dpa caused layer fragmentation and greater than ∼60 dpa resulted in layer dissolution. The chemical mixing of layers occur to a depth of ∼1 μm, consuming multiple bi-layer periods. Despite the elevated irradiation temperature (500 °C) and a slightly positive heat of mixing (+6 kJ/mol), no phase separation was observed and single-phase was retained in the mixed region. The results demonstrate that chemical mixing was facilitated by the liquid phase miscibility of Zr and Nb, which propelled the interdiffusion within the thermal spikes towards mixing.

HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY STUDY OF CRYSTALLOGRAPHY AND MORPHOLOGY OF TiC PRECIPITATES IN ARGON IRRADIATED 18Cr10NiTi STEEL

This work encompasses identification of the crystal structure and analysis of the TiC precipitates in 18Cr-10Ni-Ti austenitic stainless steel under Ar-ions irradiation. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) are used. Orientation relationship of TiC particles in surrounding matrix are indicated by HRTEM and diffraction patterns. The size of the precipitates is found to be critical: the coherency of TiC is kept at the interfaces when the precipitate is in the stage of nucleation, whereas the growth of precipitate up to 10 nm can lead to the loss of coherency in the austenitic steel. The findings suggest that the incoherent precipitate-matrix interface is an important point defect sink and contributes to inert gas bubble formation at elevated irradiation temperatures.

In-situ TEM investigation of 30 keV he+ irradiated tungsten: Effects of temperature, fluence, and sample thickness on dislocation loop evolution

In-situ irradiations with 30 keV He+ were performed on tungsten in an investigation of the influences of irradiation temperature and fluence, pre-existing dislocation and sample thickness on dislocation loop evolution including interaction, density and size. Dislocation loops with b = 1/2<111> and b =<100> were found to form in tungsten during irradiation. The ratio of 〈100〉 loops was obviously affected by irradiation temperature, fluence, sample thickness and pre-existing dislocation lines. The interaction between high density helium clusters could stimulate the formation of 〈100〉 loops in irradiated W, which was verified by Molecular Dynamic (MD) simulations. In addition, the driving force for the 〈100〉 loop formation should also be attributed to the reaction of two 1/2<111> loop variants driven by long-time and elevated temperature irradiation. The pre-existing dislocation lines were found to have a profound effect on the size, density and Burgers vector of dislocation loops. Additionally, irradiation-induced defects were likely to be absorbed by the surface sinks of thin foil during ion irradiation, resulting in the formation of a denuded zone near the surface. The in-situ observation of irradiation defect evolution will lead to an improved fundamental understanding of irradiation damage process of tungsten serviced in fusion reactor.

A modified accelerated testing method of ELDRS in extreme-low dose rate irradiation

Low dose rate radiation induced gain degradation in bipolar devices is considered to be the primary threat to the spacecraft reliability and service life. In order to examine the radiation tolerance of bipolar devices, it is recommended to use 10 m rad(Si)/s as the typical dose rate in the standards MIL-STD-883G. There is lack of solid study to prove the dose rate is sufficient enough low. Our latest experiment results showed that the enhanced low dose rate sensitivity (ELDRS) effects was not saturated at 10 m rad(Si)/s. To examine the reliability of bipolar devices in extreme low dose rate environment below 10 m rad(Si)/s in short time, we proposed a modified accelerated testing method of ELDRS effects in extreme-low dose rate irradiation based on elevated temperature irradiation and temperature-switching during irradiation, which is helpful to get quantified results in the whole low dose rate range.

The stability of γ′ precipitates in a multi-component FeCoNiCrTi0.2 alloy under elevated-temperature irradiation

Precipitation hardening by γ′ precipitates is an effective strengthening mechanism for designing novel high-entropy alloys (HEAs). The stability of these γ′ precipitates under elevated temperature irradiation is a major concern for their application in nuclear industry. In the present study, a γ′-strengthened FeCoNiCrTi0.2 HEA is irradiated using 6.4 MeV Fe3+ ions at 400 °C, 500 °C and 600 °C, respectively. After irradiation, transmission electron microscopy (TEM) and atom probe tomography (APT) has characterized the structural and compositional stability of the γ′ precipitates. The results show that the ordered L12 structure of γ′ precipitate is susceptible to the radiation damage, whereas their basic compositional features can sustain up to ∼13 dpa at these temperatures. APT reveals that the dissolution of γ′ precipitates start from the surface of the precipitates at the early stage of irradiation. Dissolution and disordering of the precipitates are dependent on the irradiation dose and temperature. APT also shows that small Ni and Ti-rich clusters form after irradiation at elevated temperatures. The behavior of γ′ precipitates under irradiation is believed to be controlled by two competing factors, displacement damage and radiation enhanced diffusion. Both can influence the radiation induced disordering/dissolution and reprecipitation.

The role of Ti and TiC nanoprecipitates in radiation resistant austenitic steel: A nanoscale study

This work encompasses an in-depth transmission electron microscopy and atom probe tomography study of Ti-stabilized austenitic steel irradiated with Fe-ions. The focus is on radiation induced segregation and precipitation, and in particular on how Ti and TiC affect these processes. A 15-15Ti steel (grade: DIN 1.4970) in two thermo-mechanical states (cold-worked and aged) was irradiated at different temperatures up to a dose of 40 dpa. At low irradiation temperatures, the cold-worked and aged materials evolved to a similar microstructure dominated by small Si and Ni clusters, corresponding to segregation to small point defect clusters. TiC precipitates, initially present in the aged material, were found to be unstable under these irradiation conditions. Elevated irradiation temperatures resulted in the nucleation of nanometer sized Cr enriched TiC precipitates surrounded by Si and Ni enriched shells. In addition, nanometer sized Ti- and Mn-enriched G-phase (M6Ni16Si7) precipitates formed, often attached to TiC precipitates. Post irradiation, larger number densities of TiC were observed in the cold-worked material compared to the aged material. This was correlated with a lower volume fraction of G-phase. The findings suggest that at elevated irradiation temperatures, the precipitate-matrix interface is an important point defect sink and contributes to the improved radiation resistance of this material. The study is a first of its kind on stabilized steel and demonstrates the significance of the small Ti addition to the evolution of the microstructure under irradiation.

Direct matter disassembly via electron beam control: electron-beam-mediated catalytic etching of graphene by nanoparticles

We report electron-beam activated motion of a catalytic nanoparticle along a graphene step edge and associated etching of the edge. The catalytic hydrogenation process was observed to be activated by a combination of elevated temperature and electron beam irradiation. Reduction of beam fluence on the particle was sufficient to stop the process, leading to the ability to switch on and off the etching. Such an approach enables the targeting of individual nanoparticles to induce motion and beam-controlled etching of matter through activated electrocatalytic processes. The applications of electron-beam control as a paradigm for molecular-scale robotics are discussed.

Influence of Irradiation Temperature on Oxidative and Network Properties of X-Ray Cross-Linked Vitamin E Stabilized UHMWPE for Hip Arthroplasty.

Previous studies have shown that increased cross-link density, reduced free radicals, and increased antioxidant grafting resulting from electron-beam irradiation at elevated temperatures improved the wear performance and the oxidative stability of vitamin E blended UHMWPE. The current study explores the impact of elevated irradiation temperature on vitamin E blended UHMWPE using X-ray. We hypothesize that the effects of temperature would be similar to those observed after electron-beam irradiation due to the relatively high dose rate of X-rays. Two X-ray doses of 80 and 100 kGy and two irradiation temperatures, that is, room temperature and 100°C were considered. The reference was Vitelene®, a vitamin E stabilized polyethylene cross-linked with 80 kGy by e-beam at 100°C. Oxidation index and oxidation induction time, as well as cross-link density, gel fraction, and trans-vinylene index, were determined, as the oxidative and network properties are decisive for the long-term implant performance. Gel fraction and oxidation induction time were significantly improved subsequently to warm irradiation in comparison with the material irradiated at room temperature. In conclusion, X-ray irradiation at elevated temperatures resulted in an increase of cross-linking and oxidative resistance of vitamin E stabilized polyethylene comparable to those of e-beam irradiated UHMWPE.

High-Temperature Nano-Indentation Creep of Reduced Activity High Entropy Alloys Based on 4-5-6 Elemental Palette.

There is a strong demand for materials with inherently high creep resistance in the harsh environment of next-generation nuclear reactors. High entropy alloys have drawn intense attention in this regard due to their excellent elevated temperature properties and irradiation resistance. Here, the time-dependent plastic deformation behavior of two refractory high entropy alloys was investigated, namely HfTaTiVZr and TaTiVWZr. These alloys are based on reduced activity metals from the 4-5-6 elemental palette that would allow easy post-service recycling after use in nuclear reactors. The creep behavior was investigated using nano-indentation over the temperature range of 298 K to 573 K under static and dynamic loads up to 5 N. Creep stress exponent for HfTaTiVZr and TaTiVWZr was found to be in the range of 20–140 and the activation volume was ~16–20b3, indicating dislocation dominated mechanism. The stress exponent increased with increasing indentation depth due to a higher density of dislocations and their entanglement at larger depth and the exponent decreased with increasing temperature due to thermally activated dislocations. Smaller creep displacement and higher activation energy for the two high entropy alloys indicate superior creep resistance compared to refractory pure metals like tungsten.

Monoclonal Antibody Dimers Induced by Low pH, Heat, or Light Exposure Are Not Immunogenic Upon Subcutaneous Administration in a Mouse Model

The presence of protein aggregates is commonly believed to be an important risk factor for immunogenicity of therapeutic proteins. Among all types of aggregates, dimers are relatively abundant in most commercialized monoclonal antibody (mAb) products. The aim of this study was to investigate the immunogenicity of artificially created mAb dimers relative to that of unstressed and stressed mAb monomers. A monoclonal murine IgG1 (mIgG1) antibody was exposed to low pH, elevated temperature, or UV irradiation to induce dimerization. Dimers and monomers were purified via size-exclusion chromatography. Physicochemical analysis revealed that upon all stress conditions, new deamidation or oxidation or both of amino acids occurred. Nevertheless, the secondary and tertiary structures of all obtained dimers were similar to those of unstressed mIgG1. Isolated dimers were administered subcutaneously in Balb/c mice, and development of antidrug antibodies and accumulation of follicular T helper cells in draining lymph nodes and spleens were determined. None of the tested dimers or stressed monomers were found to be more immunogenic than the unstressed control in our mouse model. In conclusion, both dimers and monomers generated by using 3 different stress factors have a low immunogenicity similar to that of the unstressed monomers.

Effect of elevated temperature irradiation on bipolar devices for space application

ABSTRACTThe application of elevated temperature irradiation for simulating of low dose rate degradation in bipolar devices was considered. The analysis was performed in the framework of the conversion model, which enables to estimate the radiation degradation at any dose rate, temperature and total dose numerically. The possibility of application of the conversion model for the numerical estimation of radiation-induced increase of LM111 input current under low dose rate radiation impact was demonstrated experimentally. A test method using four-stage elevated single temperature irradiation was proposed. The ability of temperature-switching approach for simulation of enhanced low-dose-rate sensitivity was estimated and discussed.

Temperature-Switching During Irradiation as a Test for ELDRS in Linear Bipolar Devices

A temperature-switching irradiation (TSI) sequence has been developed that is based on a first-principles understanding of interface-trap buildup and annealing. The dynamics of interface-trap buildup and annealing during elevated temperature irradiation are described in detail to provide background, context, and enhanced understanding of the TSI method. The method is shown to be a practical and conservative test for enhanced low-dose-rate sensitivity (ELDRS) in linear bipolar devices and ICs. Examples of TSI sequences are shown for target doses up to 200 krad(Si), a range of great practical interest for space applications. The method can be adapted for higher dose applications via similar approaches. Devices that do not exhibit ELDRS respond similar to TSI and high-dose-rate irradiation.