High Irradiation Resistance Research Articles

Complex precipitation behavior in a Co-free high entropy alloy during aging

High entropy alloys (HEAs) demonstrate high strength, thermal stability, and irradiation resistance, making them desirable for applications in nuclear reactors and other harsh environments. Many existing HEAs contain cobalt (Co), which makes them unsuitable for nuclear applications due to the long-term activation of Co. A previously studied Co-free alloy, (Fe0.3Ni0.3Mn0.3Cr0.1)88Ti4Al8, exhibits high strength but compromised ductility due to its network of brittle precipitates upon aging. This work investigates the formation mechanism and evolution of the precipitates, including L12 (Ni3Ti type, ordered face-centered cubic structure), B2 (NiAl type, ordered body-centered cubic structure), and Chi (FeCr-rich ordered α-Mn structure), in this alloy at 650 °C, the aging temperature that yields the alloy’s peak strength after 120 hours. Using ex-situ scanning electron microscopy, transmission electron microscopy, and atom probe tomography, the precipitates were characterized in terms of their composition, morphology, and crystal structure at various aging times. In addition, synchrotron-based, in-situ X-ray diffraction was used to probe the evolution of precipitates in the bulk during key phases of in-situ aging. The L12 precipitates exhibit complex growth and coarsening behavior – their coarsening starts after just 24 hours, and competition between the L12 and B2 phases arises after 72 hours leading to a decrease in L12 volume fraction. Conversely, B2 and Chi precipitates exhibit delayed nucleation and growth, and do not form in observable quantities until after 24 hours. Once formed, however, these precipitates quickly dominate the microstructure, with >50 % volume fraction after 120 hours, leading to the previously observed mechanical properties. This study provides a foundational understanding of the evolution of multi-precipitate structures in HEAs and guides future alloy development and optimization by tailoring the precipitates.

Recent Research on SiC/SiC Composites for PWR

Silicon carbide (SiC) continuous fiber reinforced SiC matrix composites (SiC/SiC) are considered as promising candidates for pressurized water reactor (PWR) due to their small neutron capture cross-section, excellent high temperature strength and irradiation resistance, etc. SPICRI have been working on the R&D of SiC/SiC composites cladding tubes for the last decade. This report will show the recent research in material development, properties and irradiation response of SiC/SiC composites. Several critical issues to be solved for PWR fuel cladding applications, such as mechanical properties, hermeticity, thermal properties and irradiation resistance are discussed here.

Investigating helium ion irradiation resistance in additively manufactured austenitic stainless steels

Additive manufacturing (AM) enables the rapid fabrication of complex shapes using engineering materials such as austenitic stainless steels and can imbue them with high irradiation resistance for use in reactor components. This is attributed to their refined grain structure and high grain boundary area. In this study, austenitic stainless steels (type 304) fabricated via direct energy deposition (DED) and powder bed fusion (PBF) techniques were irradiated with 5 MeV He ions to an approximate dose of 0.6 dpa at 300°C; subsequently, they were characterized through electron microscopy and the micro tensile testing. The results revealed that austenitic stainless steels manufactured using AM methods exhibited outstanding mechanical performance. The high performance of austenitic stainless steels fabricated through the DED technique can be attributed to their high tensile strength and excellent ductility elongation. This excellent performance is believed to be caused by the low stacking fault energy and the corresponding martensite formation during deformation. In particular, it was found that better mechanical properties were maintained even after helium irradiation, which is an important result obtained from the micro-tensile test. Even a small variation in the chemical composition and sub-microstructure of AM materials could result in improved irradiation tolerances.

Thermal and mechanical characterization of under-2-µm-thick AlCrNbSiTi high-entropy thin film

High-entropy alloys (HEAs) exhibit extraordinary physical properties such as superior strength-to-weight ratios and enhanced corrosion and oxidation resistance, making them potentially useful in energy storage and generation industries. However, thermal and mechanical properties of HEAs with various compositions vary significantly. Furthermore, these properties have rarely been investigated simultaneously owing to material or instrumentation limitations. Herein, we synthesize an HEA (AlCrNbSiTi) coating with a thickness of less than 2 μm. We customize a frequency-domain photothermal testing system to characterize the thermal and mechanical properties of the proposed coating with high accuracy. Owing to the large mixing enthalpy of the Al-Ti, Nb-Si, and Ti-Si pairs in the coating, its hardness and elastic modulus are 15.2 and 254.7 GPa, respectively, which are higher than those of previously reported HEAs. The thermal conductivity of the AlCrNbSiTi coating is characterized to be 2.90 W·m−1·K−1, within the expected range and well explained by the free-electron consistency diversity and phonon scattering from the amorphous structure. Additionally, the coating exhibits adequate wear performance, with a wear rate of 5.4 × 10−8 mm3·N−1·m−1. This relatively low thermal conductivity, combined with extraordinary mechanical properties, makes the proposed material an excellent candidate as a protective coating material for nuclear reactor components which require high strength, irradiation resistance, and thermal protection.

Microstructure and mechanical properties of a nanoscale-precipitate-strengthened reduced-activation refractory complex concentrated alloy

Reduced-activation refractory complex concentrated alloys (RARCCAs) are promising for nuclear industrial applications due to their high strength, corrosion resistance, and irradiation resistance. However, the poor phase stability of the matrix and formation of a brittle second phase result in a poor strength-ductility balance. A novel Ti0.5Hf0.25Ta0.25 RARCCA with a single bcc (body-centered cubic) phase possessing excellent strength and ductility synergy is successfully developed in this study by deliberately combining the “d-electron” method and the empirical parameters calculation. The yield and tensile strengths are 903 and 929 MPa, respectively, with an excellent ductility of approximately 22%. A new type of ω precipitate with a small size (∼1.7 nm) is introduced, contributing to a strength increment of approximately 150 MPa through shearing mechanism without sacrificing ductility. Dislocation slip dominates the deformation during tension at room temperature.

Semiconductor Detector Study for Detecting Fusion Neutrons using Geant4 Simulations

Accurate neutron flux measurements in fusion reactors are essential, in order to determine the feasibility and progress of the reaction as well as for safety issues. Semiconductor neutron detectors exhibit promising characteristics for operation in the extreme environmental conditions of fusion reactors. Silicon, Diamond and Silicon Carbide are the most studied and anticipated materials for constructing detectors with high efficiency and irradiation resistance. The ITER fusion reactor is expected to run D-D plasma measurements in the near future, so the detection of 2.45 MeV neutrons with appropriate detectors is of great and immediate importance. In the present work the study of 2.45 MeV neutrons interactions with a silicon, diamond and silicon carbide detector was made, using GEANT4 [1] simulations, in order to compare their response. An experimental study will follow at the neutron production facility of the TANDEM accelerator of the I.N.P.P. of the NCSR “Demokritos”, with detectors provided by CIVIDEC Instrumentation GmbH, so the geometry of the simulations was built accordingly. A quasi-monoenergetic neutron beam of 2.45 MeV was produced through 3H(p,n) reactions in a TiT target. Due to the low cross section of the reaction, biasing techniques were implemented in the simulation to increase the counting rate and thus producing realistic results. These biasing techniques were studied, with various tests and the parameters affecting the choice of the biasing factor are shown and discussed.

Effective self-healing behavior of nanocrystalline-amorphous laminated alloy under irradiation

An extensive investigation on the microstructural evolution of nanocrystalline–amorphous laminated alloys (NALAs) by molecular dynamics simulations and mechanistic analysis have been conducted to apprehend the interplay of complex phenomena governing structural changes in this alloy under neutron irradiation. It was discovered from the evolution profiles of free volumes, atomic unfilled spaces, and irradiation-induced vacancies that the profound structural response of the NALA was orchestrated by the rapid and spontaneous recovery of free volumes that indicate a self-healing ability in the amorphous zone, while the phenomenon of geometric atomic reconstitution in local structures governs the effective self-healing capacity for annihilated nanocrystal regions. Furthermore, a distinctive, self-migration/diffusion capture dynamics for the annihilation of defects by phase boundaries was discovered as an effective self-healing mechanism in NALAs. These findings will potentially facilitate the development of advanced nuclear materials with high irradiation resistance.

High charge collection efficiency detector based on plasma purified high-quality diamond

Diamond radiation detector is an ideal choice for the next-generation radiation detection in harsh environments, due to its small size, high irradiation resistance and fast response. However, high-purity single crystal diamond is hard to be prepared at the high growth rate due to the inevitable impurity incorporation. In this paper, based on the high-quality high-temperature/high-pressure (HPHT) single crystal diamond substrate, detector-grade single crystal diamonds material with high purity and low defect density were epitaxially grown at growth rate of about 4 μm/h by using plasma environment purification technology. It showed that the full width at half maximum of X-ray rocking curve of high-quality single crystal diamond could reach 0.007°, there was no nitrogen related impurity in PL spectrum, and the substitutional nitrogen content estimated by UV absorption spectrum was less than 10 ppb. After metallization and packaging process, the diamond detectors were prepared and the detector response under irradiation with 241 Am α-particles was realized. For the sample with fewer dislocations, the charge collection efficiency and energy resolution of this detector were 86.8 % and 7.85 % for electrons, and 96.7 % and 2.48 % for holes. The product of mobility and lifetime of electrons and holes were 1.7 × 10 −4 cm 2 V −1 and 3.7 × 10 −4 cm 2 V −1 , respectively. The high performances of the detector indicate that the current diamond detector can meet the application requirements of commercial diamond detectors. • Detector-grade diamond was prepared by plasma environment purification technology. • The high-purity single crystal diamond was grown at growth rate of about 4 μm/h. • The diamond detector with charge collection efficiency of 96.7 % was realized. • The products of mobility and lifetime of electrons and holes were 1.7 × 10 −4 and 3.7 × 10 −4 cm 2 V −1 .

Effect of addition of Nb on phase stability of equiatomic CrFeMoV alloy

Multiprincipal alloys with better high temperature properties and irradiation resistance are being explored as potential candidates for nuclear applications. This work is aimed at investigating the effect of Nb addition on the phase stability of CrFeMoV alloy. Microstructure of the as cast CrFeMoNbV alloy showed a dendritic morphology. Microsegregation in the cast alloy has been understood on the basis of partition coefficient and difference in melting point of the constituent elements. Structural analysis through Precession Electron Diffraction (PED) and 3D Automated Diffraction Tomography (ADT-3D) showed the formation of HCP intermetallic Laves phase of Fe2Nb type in a BCC matrix. The formation of this dual phase structure has been understood through in depth empirical calculations and CALPHAD simulations. Addition of Nb is shown not only to increase the lattice strain through increase in atomic size difference, but also increases the enthalpy contribution, which favors the formation of intermetallic Laves phase.

Study on irradiation effects of refractory bcc high-entropy alloy

• Refractory HEAs exhibit high thermal stabilities after heat-treatment. • The irradiation hardening of MoNbTaTiW is smaller than that of MoNbTaTi. • Refractory HEAs have higher irradiation resistance than pure tungsten. We developed body-centered cubic refractory high-entropy alloys, MoNbTaTi, MoNbTaW, and MoNbTaTiW, and explored their microstructure, and mechanical properties in order to develop a new high-irradiation resistance material suitable for fusion reactor components. Three HEAs were annealed at 1200 °C for 48 h to form single face BCC alloys, while MoNbTaW was also annealed at 1500 °C. SEM inspection and EDS mapping have both validated this result. The Vickers hardness of three HEAs was investigated, and the stable results indicate that they are all stable at elevated temperatures. Three HEAs are ion irradiated with 6.4 MeV Fe 3+ at a temperature of 500 °C, and the irradiation hardening is examined using nanoindentation. In comparison to pure tungsten, the three HEAs exhibit increased resistance to irradiation.

Kr ion irradiation study of polymer‐derived SiFeOC–C–SiC nanocomposite

AbstractThis study focuses on the pyrolysis and ion irradiation behaviors of polymer‐derived SiFeOC–C–SiC ceramic. The pyrolyzed material is composed of SiO2 and SiOC (amorphous), carbon (amorphous and turbostratic), and Fe3Si and β‐SiC (nanocrystalline). Irradiation was carried out at both room temperature and 600°C using 400 keV Kr ions with fluences of 4 × 1015 and 1 × 1016 ions cm−2, respectively. The Fe3Si and SiC nanocrystals are stable against irradiation up to 3 displacement per atom (dpa) at room temperature and up to 12 dpa at 600°C. The SiOC tetrahedrals show phase separation and minor carbothermal reduction. The high irradiation resistance and the dense, defect‐free amorphous microstructure of SiFeOC–C–SiC after prolonged irradiation demonstrate its great potential for advanced nuclear reactor applications.

The microstructure and radiation resistance of fine-grained W-0.3 wt%Y2O3 prepared by nano in-situ composite exposed to low-energy and high‑flux helium plasma

Tungsten is facing extremely harsh irradiation environmental challenges as plasma-facing materials. In this work, W-0.3 wt%Y2O3 composites fabricated by nano in-situ composite method were subjected to He plasma irradiation with 60–80 eV and 2.88 × 1022–2.3 × 1026 m−2. The microstructure, morphology, and phase evolution on the surface before and after irradiation were systematically investigated. Besides, the damage behavior and mechanism were initially analyzed. Results show that the nano-scaled Y2O3 with the size of 40–350 nm dispersed uniformly at the grain boundary and within grains of matrix, and part of it formed orientation relationship of [1̅11] (1̅1̅0) W (bcc) // [011] (400) Y2O3 (bcc) with W to significantly improve the phase interface. Surprisingly, there is a semi-coherent relationship between W matrix and Y2O3 phase. Simultaneously, the fine-grained W-0.3Y2O3 composites reveals excellent resistance to He plasma irradiation. As the irradiation dose increases, the surface morphology evolves from smooth to roughening, micro-bulges, rod-shaped and swelling, however, no nano-fuzz are observed when the irradiation dose was up to 2.3 × 1026 m−2. Besides, the chemical constitution and phase composition on surface is unchanged. Moreover, the dislocation lines, loops and rafts are observed by TEM on the surface layer, but no He bubble is formed. The high irradiation resistance may be attributed to the formation channels to release He, which can provide a strategy and idea for designing anti-irradiation W materials.

Studies on the design and properties of FeCrVTix medium-entropy alloys for potential nuclear applications

The materials' issue is one of the main bottlenecks restricting the development of nuclear energy systems. Based on the requirements of low activation, high-temperature thermal stability, high strength, high ductility, high thermal conductivity, irradiation resistance, corrosion resistance and other characteristics, the FeCrVTix medium-entropy alloys (MEAs) were designed for the working under extreme environments of the advanced nuclear energy systems. Here, thermodynamic calculation and coupling with the selection of low activation and functional elements and phase composition estimation, to MEAs are shown in the effort to design this kind of modern advanced alloy materials. Meanwhile, a kind of FeCrVTix (x=0, 0.05, 0.1, 0.2, 0.3) MEAs, as a model material, was prepared by arc melting and its above-mentioned properties were investigated. The results show that FeCrVTix MEAs have excellent properties and quite match the previous expected design, which have great potential for nuclear applications as structural materials. Most importantly, this novelty and proven method of alloy design based on the target requirements and configuration entropy has been proven to be correct and feasible, providing a new way for the design and rapid screening of new materials.

Cooperation between microporous frameworks and micron-sized channel in crystals for excellent chromate removal

The vitrification process represents an effective method for high-level radioactive waste disposal, but CrO42- can form crystalline spinels within the glass to cause the secondary leak of radioactive waste. Porous materials are widely used for trapping CrO42-, but the unsatisfied adsorbing capacity and poor selectivity of reported materials make CrO42- enrichment to be a challenging issue. Herein, a rarely hollow single-crystalline MOF (1) with ordered macro-micropores of 13 μm and 8.6 Å was obtained, exhibiting high N2 adsorption of 339.2 cm3/g and large BET surface area of 1150 m2/g. Cooperation effect between microporous frameworks and micron-sized channels in crystals endows 1 with excellent chromate removal capacity of 609 mg/g, which is a record value known to date among the anion-exchange materials for CrO42- removal. The kinetic analysis revealed that such adsorption was a pseudo-second-order adsorption process. Framework 1 possessed high pH stability and irradiation resistance, can repeatedly absorb/desorb CrO42- to some degree. More importantly, sample 1 can maintain its high CrO42- adsorption capacity after 400 kGy β irradiation, offering the promising application for CrO42- disposal in high-level radioactive waste.

Pulsed electric current joining of oxide-dispersion-strengthened austenitic steels

The solid-state joining of oxide-dispersion-strengthened (ODS) austenitic steels was achieved using a pulsed electric current joining (PECJ) process. Microstructures of the austenitic grain structures and oxide dispersions in the joint areas were characterized using electron microscopy. Negligible grain growth was observed in austenitic grain structures, while slight coarsening of oxide dispersions occurred at a short holding time. The mechanisms of the PECJ process may involve three steps that occur simultaneously, including the sintering of mechanical alloying powders in the bonding layer, formation of oxide dispersions, and bonding of the mechanical alloying powders with the base alloy. The high hardness and irradiation resistance of ODS alloys were retained in the joint areas. This research revealed the fundamental mechanisms during the PECJ process, which is beneficial for its potential applications during the advanced manufacturing of ODS alloys.

An optimization method of position resolution for gaseous thermal neutron detection based on time information

Micro Pattern Gaseous Detector (MPGD) is a promising and competitive technology for thermal neutron imaging, due to its many advantages such as high counting rate, low mass, irradiation resistance, and excellent position resolution. In order to further improve spatial resolution, a vertex reconstruction of neutron conversion tracks can be employed. Moreover, the accompanying γ-ray background also has a significant impact on the detector performance. In this work, a detector for thermal neutron detection was developed based on GEMs, with a B4C-coated Mylar foil as the converter. Track reconstruction and vertex correction were achieved with additional use of the information of each signal. The rising time and energy were utilized to improve the track reconstruction furthermore. Finally, the spatial resolution was improved to 0.23 mm from 1.01 mm significantly for thermal neutron detection.

Nano-amorphous layers improve the helium swelling resistance of a CAC-type nanocomposite

Numerous studies pay more attention to the heterophase interfaces of nanocomposites due to their effective sinks for radiation-induced point defects and traps for helium. An amorphous structure with excessive free volume also possesses high He solubility and irradiation resistance, but its effect on helium irradiation of the nanocomposites is not clear. Here, the helium irradiation effect of a crystalline/amorphous/crystalline sandwich structured W/Amorphous/Cu nanocomposite (W/A/Cu) is investigated. The results show that helium swelling resistance of a W/A/Cu nanocomposite is enhanced after introducing an amorphous layer due to strong sink strength of the crystalline/amorphous-W(Cu)/A interface and high He solubility of amorphous layers. This result sheds light on the design of radiation-tolerant materials for advanced nuclear reactor applications.

Effect of Oxygen Content on Microstructure and Tensile Properties of a 22Cr-5Al ODS Steel.

The high tensile strength and irradiation resistance of oxide dispersion strengthened (ODS) ferritic steels is attributed to the ultrafine and dispersed oxides within the matrix. The high content of oxygen and yttrium is critical for the formation of dense Y-rich oxides. However, only few studies have reported the effect of oxygen content on the microstructure and mechanical properties of ODS steels. Herein, we employed gas atomization reactive synthesis to prepare pre-alloy powders and then hot isostatic pressing (HIP) to consolidate two 22Cr-5Al ODS steels with different oxygen content. Our results showed Y-rich precipitates at and near grain boundaries of the as-HIPed alloys. Moreover, with the oxygen content increasing from 0.04 to 0.16 wt%, more precipitates precipitated in the as-HIPed alloy, and the ultimate tensile strength of the alloy was improved. However, increasing the oxygen content to 0.16 wt% led to formation of stripe and chain precipitates at and near grain boundaries, which caused a partial intergranular fracture of the as-HIPed alloy.

Constructing high-performance radiation-resistant ternary YSZ-MgO-CNT nanocomposites via tailored nanostructures

Developing long-lifetime bulk-form ceramic-based materials with high irradiation resistance is crucial for advanced nuclear systems. Here, we incorporated carbon nanotubes (CNTs) into yttria-stabilized zirconia (YSZ) and magnesia (MgO) nanocrystals to fabricate bulk YSZ-MgO-CNT nanocomposites with abundant ternary nanostructures by spark plasma sintering. To understand the role of tailored ternary nanostructure on irradiation, we investigated the microstructure and mechanical properties evolutions of the YSZ-MgO-CNT nanocomposites irradiated by multi-energy He+ ions at high temperature to different fluences. Compared with the single-phase YSZ and ultrafine-grained YSZ-MgO composites, the YSZ-MgO-CNT nanocomposites possessed higher ability to manage irradiation-induced He bubbles/defects via the defect-interface interactions of proposed “loading-unloading” and “loading-transporting-unloading” mechanisms for controlling the dynamical behaviors of He atoms/defects in the CNT-doped ternary nanostructures, thereby presenting more stable microstructure and better performance in resisting irradiation hardening. This work provides insight into the design of advanced inert matrix nuclear fuel and new nuclear waste management materials.

Research progress of the preparation of high entropy alloy coatings by spraying

In the 1990s, Ye, a scholar from China, broke the routine with a creative idea of the concept of high entropy alloys (HEAs). Since then, new alloys, which breached the traditional concept of “primary component”, have caught great attention of scientists at home and abroad. Due to their excellent properties such as high hardness, strength, wear resistance, corrosion resistance, thermal resistance, and irradiation resistance, HEAs have been considered as a new generation of thermal spray materials with immense potential for industrial applications. Previous studies show similar or even better properties of HEA coatings compared to those of the HEA block. The preparation of the coatings has become the key point since then. Spraying is one of the common methods on preparing HEA coatings, including conventional methods such as plasma spraying, supersonic flame spraying, high-velocity arc spraying, and cold spraying. With their own advantages and disadvantages, appropriate spraying methods and parameters should be selected according to different matrix and spraying materials, which will be discussed in this paper. First, the theoretical basis of the HEAs were introduced. Next, starting from different thermal spraying processes, the research and development status of plasma spraying, supersonic flame spraying, high-velocity arc spraying, and cold spraying on the preparation of HEA coatings were reviewed. Raw material selection, preparation process optimization, performance research, coating post-treatment, and other aspects of the above four thermal spraying techniques to prepare HEA coatings were systematically summarized. Finally, the three problems of limited existing thermal spraying techniques for preparing HEA coatings, limited thermal spraying materials, and aimless design of HEA coatings were proposed. Moreover, three future development issues of new thermal spraying techniques and optimization of existing techniques were discussed along with the development of high entropy ceramics, high entropy amorphous alloys, high entropy composite materials, and other new thermal spray materials. Finally, an HEA database was established to prepare HEA coatings using the concept of material genome to solve the three problems.