Nanomechanical testing of ODS steels irradiated with 1 MeV/amu heavy ions

Heavy ion beams with high damage production rate are widely used to evaluate radiation tolerance of promising nuclear reactor materials, such as oxide dispersion strengthened (ODS) alloys, including their mechanical properties. Since typical ion projected ranges do not exceed 1 micron, nanoindentation technique is the most convenient method for examination of irradiated materials. In present work we report data on radiation hardening of several ODS steels irradiated with 107 MeV Kr and 167 MeV Xe ions. Some samples were irradiated trough the special Al-foil filter in order to obtain the unfolding damage profile on the surface. The post-irradiation testing steels included conventional nanoindentation measurements and CSM for determination of possible size effects associated with indentation size effect as well as soft surface effect. Swift heavy ion induced changes in microstructure evolution were studied by transmission electron microscopy (TEM). It was found that hardening of the ODS steels irradiated with krypton and xenon ions of fission fragment energy for damage dose about 1 dpa level is in the range 5-25% (figure 1). TEM examination have revealed complete amorphization of carbide and (Y,Ti) oxide particles in ferritic matrices as a result of multiple amorphous latent track overlapping. At the same time no dissolution of nano-oxide particles was observed. This implies that radiation hardening is not due to changes in morphology of nanoparticles

Iron-filled multiwalled carbon nanotubes surface-functionalized with paramagnetic Gd (III): A candidate dual-functioning MRI contrast agent and magnetic hyperthermia structure

The authors are grateful for the financial support from the Engineering and Physical Science Research Council, UK

The influence of helium-induced defects on the migration of strontium implanted into SiC above critical amorphization temperature

The presence of radiation-induced defects and the high temperature of implantation are breeding grounds for helium (He) to accumulate and form He-induced defects (bubbles, blisters, craters, and cavities) in silicon carbide (SiC). In this work, the influence of He-induced defects on the migration of strontium (Sr) implanted into SiC was investigated. Sr-ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 1016 Sr-ions/cm2 at 600°C (Sr-SiC). Some of the Sr-SiC samples were then co-implanted with He-ions of 21.5 keV to a fluence of 1 × 1017 He-ions/cm2 at 350°C (Sr + He-SiC). The Sr-SiC and Sr + He-SiC samples were annealed for 5 h at 1,000°C. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Rutherford backscattered spectrometry (RBS). Implantation of Sr retained some defects in SiC, while co-implantation of He resulted in the formation of He-bubbles, blisters, and craters (exfoliated blisters). Blisters close to the critical height and size were the first to exfoliate after annealing. He-bubbles grew larger after annealing owing to the capture of more vacancies. In the co-implanted samples, Sr was located in three regions: the crystalline region (near the surface), the bubble region (where the projected range of Sr was located), and the damage region toward the bulk. Annealing the Sr + He-SiC caused the migration of Sr towards the bulk, while no migration was observed in the Sr-SiC samples. The migration was governed by “vacancy migration driven by strain fileds.

Reversible Magnetization of Ferrite-Garnet Film by Polarized Light

The effect of low-powered polarized light on magnetic characteristics of ferrimagnetic garnet films has been studied at room temperatures by means of magneto-optical Faraday effect. A local magnetization of the film, occurred under the illumination, was carried out in the direction determined by orientation of polarization vector. The effect, accompanied by the domain structure reconstruction, caused also changes of the mechanical strain and dichroism. The spectral, polarization, amplitude and temperature dependences were investigated in order to explain the origin of such a photomagnetic effect. Peculiarities of the effect and their correlation with parameters of the films and illuminated light are discussed in terms of the developed early models, based on light induced recharging of the polarization-sensitive anisotropic centres. The additional magnetostriction mechanism is assumed to be responsible for displaying of the observed phenomena

Congruent patterns of genetic divergence revealed by allozymes and sequencing supports the existence of high levels of gene flow in a burrowing freshwater crab

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TEM Study of Helium Porosity Formation in ODS Ferritic Alloys during Post-Irradiation Annealing

Секция 2. Радиационные эффекты в твердом теле = Section 2. Radiation Effects in SolidsTransmission electron microscopy has been applied to study the formation of helium porosity both in conventional ferritic steel AISI410S and in two oxide dispersion strengthened (ODS) ferritic alloys: experimental ODS Cr16 steel and advanced ODS EP450 steel considered as promising structural materials for fuel cladding. The samples were implanted with low-energy helium ions at room temperature and annealed at temperature of 1073 K (0.6T m ) for 30 minutes. TEM investigation after such heat treatment has revealed a bimodal size distribution of helium bubbles in AISI410S and ODS Cr16 steels: large-sized bubbles with a large total volume were found in vicinity to grain boundaries (GBs), dislocations or outer surface, while small bubbles were observed inside of grain interiors (GIs). At the same time, helium bubbles in EP450 steel were found to be uniformly distributed throughout the grain body. It is suggested that helium bubble migration and coalescence in ODS EP450 is significantly accelerated due to its permanent cold-hardened state in comparison with two other steels. It is shown that presence of dispersed nano-oxides in ODS alloys does not have a noticeable effect on gas swelling in studied ODS alloys

TEM Study of Helium Porosity Formation in ODS Ferritic Alloys during Post-Irradiation Annealing

Секция 2. Радиационные эффекты в твердом теле = Section 2. Radiation Effects in SolidsTransmission electron microscopy has been applied to study the formation of helium porosity both in conventional ferritic steel AISI410S and in two oxide dispersion strengthened (ODS) ferritic alloys: experimental ODS Cr16 steel and advanced ODS EP450 steel considered as promising structural materials for fuel cladding. The samples were implanted with low-energy helium ions at room temperature and annealed at temperature of 1073 K (0.6T m ) for 30 minutes. TEM investigation after such heat treatment has revealed a bimodal size distribution of helium bubbles in AISI410S and ODS Cr16 steels: large-sized bubbles with a large total volume were found in vicinity to grain boundaries (GBs), dislocations or outer surface, while small bubbles were observed inside of grain interiors (GIs). At the same time, helium bubbles in EP450 steel were found to be uniformly distributed throughout the grain body. It is suggested that helium bubble migration and coalescence in ODS EP450 is significantly accelerated due to its permanent cold-hardened state in comparison with two other steels. It is shown that presence of dispersed nano-oxides in ODS alloys does not have a noticeable effect on gas swelling in studied ODS alloys

High-Energy Heavy Ion Tracks in Nanocrystalline Silicon Nitride

At present, silicon nitride is the only nitride ceramic in which latent ion tracks resulting from swift heavy ion irradiation have been observed. Data related to the effects of SHIs on the nanocrystalline form of Si3N4 are sparse. The size of grains is known to play a role in the formation of latent ion tracks and other defects that result from SHI irradiation. In this investigation, the effects of irradiation with high-energy heavy ions on nanocrystalline silicon nitride is studied, using transmission electron microscopy techniques. The results suggest that threshold electronic stopping power, Set, lies within the range 12.3 ± 0.8 keV/nm to 15.2 ± 1.0 keV/nm, based on measurements of track radii. We compared the results to findings for polycrystalline Si3N4 irradiated under similar conditions. Our findings suggest that the radiation stability of silicon nitride is independent of grain size