Effects of oxygen concentration and irradiation defects on the oxidation corrosion of body-centered-cubic iron surfaces:A first-principles study

Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by the adsorption/solution of oxygen atoms on/under body-centered-cubic(bcc) iron surfaces, and diffusion of oxygen atoms on the surface and in the near-surface region. Energetic results indicate that oxygen atoms prefer to adsorb at hollow and long-bridge positions on the Fe(100) and(110) surfaces, respectively. As the coverage of oxygen atoms increases, oxygen atoms would repel each other and gradually dissolve in the near-surface and bulk region. As vacancies exist, oxygen atoms are attracted by vacancies, especially in the near-surface and bulk region. Dynamic results indicate that the diffusion of O atoms on surfaces is easier than that into near-surface, which is affected by oxygen coverage and vacancies. Moreover, the effects of oxygen concentration and irradiation on oxygen density in the near-surface and bulk region are estimated by the Mc Lean’s model with a simple hypothesis.

Temperature-dependent synergistic evolution mechanism of rhenium and irradiation defects in tungsten-rhenium alloys

We have systemically investigated the synergistic evolution of rhenium(Re)and irradiation defects in tungsten(W)-Re alloys under different temperatures and irradiation doses using object Kinetic Monte Carlo method.Our results revealed the underlying mechanism for the transition of Re effect on W from beneficial to harmful during the Re-defects evolution with the increase of irradiation dose,in which tem-perature always plays a critical role.On the one hand,Re will significantly promote the defect annihila-tion at low irradiation doses and high temperatures,thereby effectively reducing their sizes and number densities.This is due to the formation of stable Re-SIAs complexes that can be eliminated by the mobile vacancy-type defects,whereas the transition of the migration pattern of SIAs only plays a weak role in the defect recombination in W-Re system.On the other hand,with the increase of irradiation dose,Re will aggregate to form Re-rich clusters or even precipitates.Interestingly,the formation mechanism of Re-rich clusters is also dependent on temperature.At low temperatures,the interstitial-mediated mech-anism plays a crucial role in the Re-rich cluster formation,while at high temperatures,both SIA-type and vacancy-type defects will act as the transport carriers of Re to promote their clustering.Accordingly,the critical conditions for the transition of Re from beneficial to harmful and the formation of Re-rich clusters at different tem peratures and irradiation doses are given with the help of the phase diagram.Our work presents the temperature dependence of the synergy of Re and irradiation defects in W-Re in fusion-relevant environment,which provides a good reference for the development of radiation-resistant materials and the prediction of W performance in fusion reactors.

The effects of fast neutron irradiation on oxygen in Czochralski silicon

The effects of fast neutron irradiation on oxygen atoms in Czochralski silicon （CZ-Si） are investigated systemically by using Fourier transform infrared （FTIR） spectrometer and positron annihilation technique （PAT）. Through isochronal annealing, it is found that the trend of variation in interstitial oxygen concentration （[Oi]） in fast neutrons irradiated CZ-Si fluctuates largely with temperature increasing, especially between 500 and 700℃. After the CZ-Si is annealed at 600℃, the V4 appearing as three-dimensional vacancy clusters causes the formation of the molecule-like oxygen clusters, and more importantly these dimers with small binding energies （0.1-1.0eV） can diffuse into the Si lattices more easily than single oxygen atoms, thereby leading to the strong oxygen agglomerations. When the CZ-Si is annealed at temperature increasing up to 700℃, three-dimensional vacancy clusters disappear and the oxygen agglomerations decompose into single oxygen atoms （O） at interstitial sites. Results from FTIR spectrometer and PAT provide an insight into the nature of the [Oi] at temperatures between 500 and 700℃. It turns out that the large fluctuation of [Oi] after short-time annealing from 500 to 700℃ results from the transformation of fast neutron irradiation defects.

Microstructure evolution of T91 steel after heavy ion irradiation at 550℃

Fe-Cr ferritic/martensitic(F/M)steels have been proposed as one of the candidate materials for the Generation IV nuclear technologies.In this study,a widely-used ferritic/martensitic steel,T91 steel,was irradiated by 196-MeV Kr^(+)ions at 550℃.To reveal the irradiation mechanism,the microstructure evolution of irradiated T91 steel was studied in details by transmission electron microscope(TEM).With increasing dose,the defects gradually changed from black dots to dislocation loops,and further to form dislocation walls near grain boundaries due to the production of a large number of dislocations.When many dislocation loops of primary a0/2<111>type with high migration interacted with other defects or carbon atoms,it led to the production of dislocation segments and other dislocation loops of a0<100>type.Lots of defects accumulated near grain boundaries in the irradiated area,especially in the high-dose area.The grain boundaries of martensite laths acted as important sinks of irradiation defects in T91.Elevated temperature facilitated the migration of defects,leading to the accumulation of defects near the grain boundaries of martensite laths.

Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO_2 single crystals

Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO2 single crystals（SCs）.To tune their magnetism,Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively.The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO2.Meanwhile,a new CuO-like species present in the sample was found to be dissolved after the post-irradiation.Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions,while these ions are directly involved in boosting the absorption in the visible region.

Atomistic Insights into the Irradiation Resistance of Co-Free High Entropy Alloy FeMnNiCr

We have investigated the displacement cascade irradiation resistance behavior of a cobalt-free high entropy alloy FeMnNiCr using molecular dynamics simulations.The results show that defects in FeMnNiCr form in small clusters,and their migration is significantly inhibited,leading to a higher defect recombination rate and a lower number of residual defects compared to Ni.Additionally,FeMnNiCr exhibits a longer thermal peak life and lower thermal conductivity compared to Ni,providing a longer time for defect migration and combining.The migration of defect clusters in FeMnNiCr displays three-dimensional properties,attributed to its high chemical disorder.After prolonged irradiation,defects in FeMnNiCr stabilize as small clusters,whereas point defects in Ni tend to form large defect clusters and evolve into dislocations.Considering the feature of absence of the element cobalt,our results imply that FeMnNiCr has great potential in application in nuclear energies.

Infrared studies of vacancy-oxygen-related complexes in electron-irradiated Czochralski-silicon

The oxygen-related defects in CZ silicon during electron irradiation(1.5 MeV)and subsequent annealing in the range of 150-600℃were investigated by means of FTIR.In the electron irradiation CZ-Si,vacancy-oxygen complex is one of the dominant defects and its concentration is proportional to electron dose but not related to oxygen concentration.In this work,it was focused on the identification of the weak band at 860 cm^(-1)which was originated from asymmetrical stretching vibrations of an oxygen atom in the negative VO complex.It exhibits the same thermal stability with neutral VO band at 830 cm^(-1).In addition,the intensity of 889 cm-1 band has never been observed to exceed that of the A-center,implying that only a partial transformation of VO into VO_(2)does occur.

Damage Characteristics of TiD_2 Films Irradiated by a Mixed Pulsed Beam of Titanium and Hydrogen Ions

Titanium deuteride is an important nuclear material used in the field of nuclear technology, and further research is needed into TiD2 films irradiated by pulsed ion beams of the vacuum arc discharge with hydrogen. In the current study, these irradiated TiD2 films have been investigated using scanning electronic microscopy and slow positron annihilation techniques. Both the thermal effect and irradiation defects of TiD2 films were studied, following their irradiation with mixed pulsed ion beams of titanium and hydrogen ions. It is found that the thermal effect is trivial on the irradiated surfaces, and the dominant effect is irradiation defects which can be enhanced by repetitive shots and is characterized by the inner diffusion of irradiation defects.

TEM Foil Preparation from Irradiated Metallic Materials： A Practical Approach

This paper focuses on work related to post irradiation examination of 300-series austenitic stainless steel taken from reactor vessel internals of PWR. High neutron irradiation dose in NNP＇s leads to a degradation of microstructure of the material in a nano-metric scale. Hence, it is important to characterize the irradiated materials to understand the physical basis of the degradation mechanisms. Microstructural characterization of neutron-irradiated materials by TEM requires enhanced sample preparation methodologies, which commonly needs general improvements regarding particular experiment to be performed. In this study, the authors have developed methodology specialized in 1 mm TEM thin foil preparation from a deformed shank of a broken miniaturized tensile specimen. TEM foil size in current studies is smaller than standard because of the small shank diameter and high radioactivity of the studied material. The reduction of the TEM foil radioactivity to minimum is crucial to perform EDX chemical analysis and to increase the EDX detector lifetime. This paper describes whole process from bulk sample handling, including remote-controlled material cutting in shielded hot-cells and disc polishing in glow-boxes, up to the final procedure of electrolytic-polishing of electron transparent 1 mm TEM foils. Eventually, results of TEM microanalysis of radiation-induced defects were present.