Search

• Oxide film was formed after 350 °C/10 MPa water corrosion. • An obvious increment of S value was observed in irradiated & corroded specimens. • Irradiation promoted the production and accumulation of corrosion-related defects. • Corrosion-related defects induced the formation of cracks on the dense oxide films. To understand irradiation accelerated the corrosion behavior further, the early-stage aqueous corrosion-related behavior was investigated in heavy ion irradiated P92 ferritic/martensitic alloy by multiple characterization techniques. The oxide film was formed at 350 °C/10 MPa water for 80 h. The surface morphology of irradiated specimen was different from that of unirradiated specimen. Many grains were fused together in irradiated specimen. Doppler broadening spectroscopy of slow positron beam shows that the existence of irradiation defects could accelerate the production and accumulation of corrosion-related defects in the deeper region of the oxide film. [ABSTRACT FROM AUTHOR]

The formation of helium bubble precursors, i.e., helium-vacancy complexes, was investigated for Fe9Cr alloy, which was uniformly irradiated by using 100 keV helium ions with fluences up to 5 × 10 16 ions/cm 2 at RT, 523, 623, 723, and 873 K. Helium-irradiation-induced microstructures in the alloy were probed by positron annihilation technique. The results show that the ratio of helium atom to vacancy (m/n) in the irradiation induced He m V n clusters is affected by the irradiation temperature. Irradiated at room temperature, there is a coexistence of large amounts of He m V 1 and mono-vacancies in the sample. However, the overpressured He m V n (m > n) clusters or helium bubbles are easily formed by the helium-filled vacancy clusters (He m V 1 and He m V n (m ≈ n)) absorbing helium atoms when irradiated at 523 K and 823 K. The results also show that void swelling of the alloy is the largest under 723 K irradiation. [ABSTRACT FROM AUTHOR]

We have studied the effect of isothermal annealing on the evolution of the open-volume defect and the Cu precipitate in deformed Fe0.15Cu, Fe0.3Cu and Fe0.6Cu alloys. Using the coincidence Doppler broadening, positron annihilation lifetime and the S-W couples, the evolution of local electronic circumstance around the annihilation sites, open-volume defects and interaction between open-volume defects and Cu precipitates were measured as a function of the isothermal annealing temperatures. Cold rolling deformation induced an obvious increment in S parameters due to the formation of open-volume defects. Annealing not only resulted in gradual recovery of open-volume defects and Cu thermal precipitation, but also promoted the combination and interaction between defects and Cu precipitates. The interaction between open-volume defects and Cu precipitates was revealed clearly by the view point of S-W relationship. The S-W interaction for the different Cu m V n complexes was also calculated theoretically by MIKA-Doppler, which supports our experimental observations qualitatively. The results indicate that open-volume defects were formed first after cold rolling, followed by the Cu precipitation and recovery of open-volume defects, Cu precipitates recovered at the end. It is interesting that the trajectory of (S, W) points with increasing annealing temperature formed a similar closed “Parallelogram” shape. It is benefit for revealing the behavior of Cu thermal precipitation and their evolution in various Cu-bearing steels under thermal treatment. In addition, we also investigated the Cu content effect on the Cu precipitation in FeCu alloys, and the Cu precipitate phenomenon was enhanced in higher Cu content alloys. [ABSTRACT FROM AUTHOR]

The Fe1.0Cu alloy was irradiated by 2 MeV Fe ions to a peak dose of 0.06dpa, 0.45dpa and 1.35dpa, respectively. The irradiation evolution of Cu precipitates in Fe1.0Cu alloy was studied at various depths by positron annihilation spectroscopy. The values of the S parameters directly indicate the formation of vacancy clusters. The S-W relationship showed that Cu n V m complexes (n > m) dominated the microstructure in the track region. Vacancy clusters and Cu n V m complexes (n < m) were the main defect types in the damage region. There finding were supported by the results of the performed theoretical calculations. The coincidence Doppler broadening showed that the Cu precipitates formed easily at a low irradiation dose, and that the irradiation-induced Cu precipitation was enhanced by the increase of the irradiation dose in the track region. We showed that the Cu precipitates finally reach a steady-state morphology under multiple active processes. [ABSTRACT FROM AUTHOR]

Well-annealed 316L stainless steel was first cold rolled to 10% and 20% reductions in thickness and then irradiated by 50 keV He+to a dose of 1 × 1020He+/m2at room temperature. Thermal desorption spectroscopy was used to investigate the helium desorption behaviour at different helium trapping states. The results showed that high-density dislocations had stronger inhibitory effect for helium desorption at temperatures from 800 to 1200 K. Positron annihilation Doppler broadening spectroscopy measurements were used to investigate the distribution of helium irradiation-induced defects. TheS–Eand ΔS–Eplots clearly demonstrated that the helium irradiation-induced defects were trapped and restricted in motion by dislocations. The interaction between dislocations and helium irradiation-induced defects in deformed 316L stainless steel was investigated. [ABSTRACT FROM PUBLISHER]

Transmutation helium may causes serious embrittlement which is considered to be due to helium from clustering as a bubble in materials. Suppression of transmutation helium can be achieved by introducing trapping sites such as dislocations and impurities in materials. Here, effects of intentionally-induced dislocations and hydrogen on helium migrate and release behaviors were investigated using thermal desorption spectrometry (TDS) technique applied to well-annealed and cold-worked Fe9Cr alloys irradiated by energetic helium/hydrogen ions. Synchronous desorption of helium and hydrogen was observed, and the microstructure states during helium release at different temperatures were analyzed. High thermally stable He n D type complexes formed in cold-worked specimens, resulting in the retardation of helium migration and release. The existence of hydrogen will strongly affect the thermal helium desorption which could be reflected in the TDS spectrum. It was confirmed that hydrogen retained in the specimens can result in obvious delay of helium desorption. [ABSTRACT FROM AUTHOR]

We irradiated three 9Cr alloys: Fe9Cr model alloy, reduced-activation ferritic/martensitic (RAFM), and advanced oxide dispersion strengthened ferritic (RAFM-ODS) alloys, with 100keV He ions at 723K to the peaked concentration of 6500 appm (low helium level) and 65000 appm (high helium level), respectively. The question of helium-driven swelling in Fe9Cr, RAFM, and RAFM-ODS alloys was investigated by multiple characterizations. Homogeneous helium bubbles, main in the form of V m He n (n < m), nucleated on different sinks, producing swelling behavior and dominating the microstructures of irradiated Fe9Cr, RAFM, and RAFM-ODS steels. The consequent swelling rate values in Fe9Cr, RAFM, and RAFM-ODS were ∼ 0.15% (1.33%), ∼ 0.058% (0.83%), and ∼ 0.048% (0.73%) in the low (high) levels, respectively. The RAFM-ODS steel exhibits better tolerance to helium bubble swelling and superior grain size stability than Fe9Cr and RAFM, which is manifested by the smaller average sizes and the lower number densities of bubbles. It can be attributed that the oxides in RAFM-ODS steel could provide more effective helium trapping sites that sequester the helium into smaller bubbles and away from the precipitate-matrix interfaces and grain boundaries. In addition, the existence of high density of oxide particles could also delay desorption peaks of helium atoms from RAFM-ODS steel compared to RAFM and Fe9Cr. [ABSTRACT FROM AUTHOR]

Fe–0.6%Cu alloy was irradiated with H ions to 0.1 dpa, and then annealed for 30 min from 150 °C to 500 °C. We focused the evolution of Cu precipitates in irradiated Fe–0.6%Cu alloy after the isochronal annealing from the perspective of positron annihilation. The ΔW parameters after thermal annealing (400 °C and 500 °C) were much larger than that induced by 0.1 dpa H irradiation. Annealing could promote the aggregation of the Cu-vacancy complexes, and form the Cu cluster–vacancies complexes. When the vacancy-like defects recovered around 500 °C, it meant the formation and growing of the defect-free Cu precipitates. [ABSTRACT FROM AUTHOR]

Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He2+irradiation, (ii) H+irradiation and (iii) He2+irradiation followed by H+irradiation, at temperature 450 °C. The presences of vacancy defects, represented by ∆SHe+Hparameter, induced by sequential irradiations was larger than the sum of defects, ∆SHeparameter + ∆SHparameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy. [ABSTRACT FROM AUTHOR]

The correlation between Cu precipitates and vacancy-like defects in three Fe–Cu model alloys, Fe–0.15%Cu, Fe–0.3%Cu and Fe–0.6%Cu, irradiated at 400 °C with hydrogen ions at doses from 0.045 to 0.45 dpa, were revealed by positron annihilation spectroscopy. The formation of vacancy-like defects surrounded by tiny Cu precipitates induced the increment of the S and W parameters after irradiation. The peak value of the relative W parameter (ΔW/W), as the high momentum information on Cu precipitates, located in the track region and decreased with irradiation dose increased from 0.045 dpa to 0.45 dpa. The information on high momentum depended on the coverage fraction of the defects by Cu atoms. The effect of the irradiation dose, the irradiation depth and the Cu content on the Cu coverage fraction of the defects has been investigated in the present work. [ABSTRACT FROM AUTHOR]

P92 alloy, a candidate structural material for supercritical water reactors, was irradiated with 1 MeV Fe ions at 1, 3, and 7 dpa at room temperature, 300, 450, and 550°C. Slow positron beam Doppler broadening spectroscopy was used to characterize the evolution of the open-volume defects. Irradiation of the Fe9Cr alloy at 300°C induced an unexcepted phenomenon in which the S parameter decreased with an increasing irradiation dose; the phenomenon was ascribed to the pinning effect of Cr on dislocation loops, which promoted the recovery of vacancies. Whereas the reduction in the S parameter was generally inhibited in the P92 alloy. These distinctions are related to the evolution of vacancies. We show that the migration of vacancies hindered by C atoms is mainly related to carbon–vacancy complexes in the P92 alloy at approximately 300°C. As the irradiation temperature increased, the complexes gradually dissociated, and the vacancies were captured and annihilated with interstitial atoms. A better understanding of the evolution of vacancies is helpful for investigating irradiation swelling. [ABSTRACT FROM AUTHOR]

The effect of annealing on V m H n complexes and Cu precipitate behaviours in hydrogen ion irradiated Fe and Fe–0.3%Cu alloys was investigated by positron annihilation spectroscopy using a slow positron beam. The results of S parameters indicated that the room temperature irradiation was benefit for the formation of the V m H n complex compared to the elevated temperature irradiation. The S – W results confirmed the formation of Cu precipitates in Fe–0.3%Cu even at the irradiation dose of 0.1 dpa. The formation of the evident S value peaks in the damage region after annealing treatment suggested that the V m H n complexes were broken and a larger of hydrogen atoms were escaping. The residual vacancy defects would migrate towards both the surface region and the opposite direction with the increasing annealing temperature. [ABSTRACT FROM AUTHOR]

The reduced activation martensitic steel was irradiated with 250 keV He 2+ to 3000 appm and 130 keV H + to 15,000 appm alone and in sequence at 450 °C. The S – W curve obtained by the positron beam Doppler broadening spectra reveals that (He, H)–V complexes were induced by irradiation. The S parameters show that the H irradiation can decrease defects by forming H–V complexes. The He irradiation can form He–V complexes and the sequentially implanted H can accelerate the formation of (He, H)–V complexes. Hardening induced by He+H sequential irradiation is greater than that by He or H ion irradiation alone, suggesting synergistic effects of He and H on defects and hardening. [ABSTRACT FROM AUTHOR]

Abstract: Alloy 718 is a nickel-base superalloy whose strength derives from γ′(Ni3(Al,Ti)) and γ″(Ni3Nb) precipitates. The evolution of the precipitates in alloy 718 irradiated with argon ions at elevated temperature were examined via transmission electron microscopy. Selected-area electron diffraction indicated superlattice spots disappeared after argon ion irradiation, which showing that the ordered structure of the γ′ and γ″ precipitates became disordered. The size of the precipitates became smaller with the irradiation dose increasing at 290°C. [Copyright &y& Elsevier]

The irradiation-induced precipitates in argon ion-irradiated austenitic stainless steel at 550°C were examined via transmission electron microscopy. The selected-area electron diffraction patterns of precipitates indicated unambiguously that the precipitates were Cr23C6 carbides. It was observed directly for the first time that irradiation-induced Cr23C6 precipitates formed at dislocation loops in austenitic stainless steel, and coarsened with increasing irradiation dose. [ABSTRACT FROM AUTHOR]

Abstract: In present work, the irradiation damage in nickel-base alloy C-276 irradiated with Ar-ions was studied. Specimens of C-276 alloy were subjected to an irradiation of Ar-ions (with 120keV) to dose levels of 6 and 10dpa at 300 and 550°C, respectively. The size distributions and densities of dislocation loops caused by irradiation were investigated with transmission electron microscopy. Irradiation hardening due to the formation of the loops was calculated using the dispersed barrier-hardening model, showing that irradiation hardening was greatest at 300°C/6dpa. The microstructure evolution induced by Ar-ion irradiation (0–10dpa) in nickel-base alloy C-276 has been studied using a multi-scale modeling code Radieff constructed based on rate theory, and the size of dislocation loops simulated by Radieff was in good agreement with the experiment. [Copyright &y& Elsevier]

Abstract: Irradiation damage in P92 ferritic/martensitic steel irradiated by Ar+ ion beams to 7 and 12dpa at elevated temperatures of 290°C, 390°C and 550°C has been investigated by transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The precipitate periphery (the matrix/carbide interface) was amorphized only at 290°C, while higher irradiation temperature could prevent the amorphization. The formation of the small re-precipitates occurred at 290°C after irradiation to 12dpa. With the increase of irradiation temperature and dose, the phenomenon of re-precipitation became more severe. The voids induced by irradiation were observed after irradiation to 7dpa at 550°C, showing that high irradiation temperature (≥ 550°C) was a crucial factor which promoted the irradiation swelling. Energy dispersive X-ray analysis revealed that segregation of Cr and W in the voids occurred under irradiation, which may influence mechanical properties of P92 F/M steel. [Copyright &y& Elsevier]

This paper investigated oxide film of P92 steel in 300 °C/10 MPa water at different corrosion time. The surface morphology, phase structure and micro-defects were investigated by scanning electron microscope, X-ray diffraction and positron annihilation spectroscopy. The results reveal the formation of double oxide film, the outer oxide film was mainly composed of magnetite and the inner oxide film was composed of magnetite and FeCr spinel. The positron annihilation lifetimes spectra shows that the average size of defects increases with the increase of corrosion time. Doppler broadening spectroscopy of slow positron beam indicates that the outer oxide film structure was relatively dense in the initial stage of corrosion. The inner oxide film was characterized with relative loose structure due to the increase of defects size and density. [ABSTRACT FROM AUTHOR]

In the fusion reactors, plasma facing materials (PFMs) will be bombarded by large amounts of energetic particles, including helium (He) atoms. These metal-insoluble He atoms are prone to self-trapping or are trapped by vacancies, dislocation cores or grain boundaries, aggregating to form high concentration He bubbles which leads to serious degradation of the PFMs' properties. Studying the initial stages of He-defect interactions becomes increasingly important because it not only helps us understand the formation mechanism of He bubbles but also provides insight to help design new irradiation-resistant PFMs. In this work, we used the positron annihilation Doppler broadening spectroscopy (DBS) and secondary ion mass spectrometry (SIMS) to explore the evolutions of the interactions between vacancy-type defects and He and the retention of He in the nanochannel W film irradiated with 190 keV He+ ions to different fluences under different temperatures. It is found that the presence of a nanochannel structure accelerates the release of He from the film even at low irradiation fluences, and the release of He is significantly enhanced at higher fluences, thus inhibiting or delaying the formation of large He-vacancy clusters in the nanochannel W film. Both irradiation fluence and temperature have significant influence on the formation and evolution of He-vacancy clusters, and the evolution of these microstructure also causes hardness changes. • The nanochannel structures facilitate He release from the film even at relatively low fluences. • Combined the advantage of DBS and SIMS methods to explore the evolution of helium-vacancy complex. • The fluence and temperature have great influence on the evolution of vacancy-type defects, He retention and hardness. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of interaction between H and He ions on micro-defects in Fe9Cr alloy, well-annealed Fe9Cr alloy were pre-damaged firstly with 1 MeV Ni ions to a dose of 3.4 × 1013/cm2, and then irradiated with single (H or He) ion beam and sequential (H/He or He/H) ions beam. The irradiation were performed with 50 keV H ions, 80 keV He ions with doses of 1 × 1016/cm2 and 2 × 1015/cm2 at 723 K, respectively. Results of slow positron beam show that the S parameter decreased obviously after single (H or He) ions beam irradiation compared to the pre-damaged specimen, which indicate H or He (H n or He n) clusters deposit at the damage area caused by Ni ion irradiation and they occupy vacancy sites (V m), resulting in the formation of numerous H n V m or He n V m clusters. The S parameter induced by He/H ions sequential irradiation didn't change significantly compared to that by single He ion irradiation. However, obvious increment of the S parameter induced by H/He ion sequential irradiation is higher than that induced by singe H ion irradiation. The binding energy of H n V m He is larger than He n V m H, and it is difficult for subsequent H ions irradiation to decompose the He n V m complexes. [ABSTRACT FROM AUTHOR]

Abstract The aim of investigating the annealing effect induced by helium/hydrogen ion irradiation on the micro-defects of ferritic/martensitic (FM) steel is to gain a basic understanding on the development of fusion reactor components. In this study, 250 keV He2+ and 130 keV H+ were used for irradiation. Then, micro-defects were annealed isochronally between 423 K and 673 K, and were monitored by the slow positron beam Doppler broadening technique. The results revealed that the He ions implanted into the steels combined with vacancies to form He n V m clusters, and were likely to grow and form overpressured He n V m clusters by thermal activation. The S-W line of the irradiated specimen deviated the line segment, which indicates the formation of overpressured He n V m clusters in the He-irradiated steel. Moreover, the ΔS-E curves indicate residual vacancies that were induced by He-irradiation at 723 K and later migrated toward the bulk of the sample at 423 K. Subsequently, the vacancies tended to migrate to the sample surface as the annealing temperature increased. The S parameter of the He+H-irradiated sample was much larger than that of all other samples, owing to the synergy effect of H and He. After annealing at 423 K, the H-V clusters decomposed and the hydrogen atoms in the He+H-irradiated sample escaped from the surface leaving a large number of vacancies. [ABSTRACT FROM AUTHOR]

Here we demonstrate that the performance of TiO 2 electrodes for photoelectrochemical water oxidation can be effectively enhanced through oxygen vacancy doping. The ion irradiation is a simple method to introduce oxygen vacancies on the surface and into the interior of TiO 2 for making oxygen-deficient titania (TiO 2-x ). The TiO 2-x thin films exhibit obvious increase in the performance of photoelectrochemical water splitting under light irradiation. The photoconversion efficiency η of the TiO 2-x photoanode is 0.5-fold higher than that of the pristine TiO 2 photoanode, which benefits from the introducing of oxygen vacancies produced by ion irradiation. While the irradiation-induced titanium vacancies act as trapping centers for charge carriers and decrease the photoelectrochemical performance of the samples. Positron annihilation spectroscopy (PAS) was used to study the type of the formed vacancies. Combining experimental with theoretical study, this study demonstrates that ion irradiation technique combing with thermal annealing could be an effective way to enhance the performance of photoanode for water splitting. [ABSTRACT FROM AUTHOR]

Ab initio calculations are implemented to investigate the structural and helium diffusion behaviour in Fe 6.25 at.% Cr binary alloys based on FCC–Fe. Our simulation results confirmed that the increase of Cr contents in the AFM phase is beneficial to strengthen the shear deformation resistance and hardness of the alloys, and also leads to greater lattice distortion. The presence of Cr atoms accelerates the migration of mono-helium atoms between tetrahedral and octahedral gaps in varying degrees, but greatly impedes the migration of helium atoms between tetrahedral interstitials or within the main lattice. The tetrahedral model is more stable than the octahedral model by 0.213 and 0.433 eV under the AFM and NM phase, respectively. The stability of the helium gap models depends on the electrostatic interaction between helium and surrounding metal atoms, and impurity atoms and magnetism do not directly affect its stability. There is a strong bonding interaction between Fe and Cr atoms, and the presence of interstitial helium atom results in net charge redistribution. This study provides valuable information for the interpretation of complex experimental phenomena. [ABSTRACT FROM AUTHOR]

High-energy resolution core-level spectroscopies, including a group of different techniques to obtain element-specific information of the electronic structure around an absorption site, have become powerful tools for studying the chemical state, local geometric structure, and the nature of chemical bonding. High-resolution x-ray absorption and x-ray emission spectroscopies are well-established experimental techniques but have always been limited by the number of emitted photons and the limited acceptance of solid angles, as well as requiring high energy stability and repeatability for the whole experimental setup. A full-cylindrical x-ray spectrometer based on flexible HAPG (highly annealed pyrolitic graphite) mosaic crystals is an effective solution for the above issues. However, large-area HAPG remains expensive and is often not easy to access. Here, we present an alternative approach by using segmented single crystals (Si and Ge) with different orientations instead of the HAPG as a dispersive element. The proposed method drastically improved the energy resolution up to 0.2–2 eV in the range of 2–10 keV. High-pressure x-ray emission and resonant x-ray emission spectra are presented to demonstrate the capabilities of the instrument. The new design is particularly suitable for high-resolution spectroscopy applications at fourth-generation synchrotron radiation sources or free-electron lasers. [ABSTRACT FROM AUTHOR]

An element analysis method, coincidence Doppler broadening spectroscopy of slow positron annihilation, was employed to detect helium in ion-irradiated Fe9Cr alloys. Spectra with higher peak to background ratio were recorded using a two-HPGe detector coincidence measuring system. It means that information in the high-momentum area of the spectra can be used to identify helium in metals. This identification is not entirely dependent on the helium concentration in the specimens, but is related to the structure and microscopic arrangement of atoms surrounding the positron annihilation site. The results of Doppler broadening spectroscopy and transmission electron microscopy show that vacancies and dislocations were formed in ion-irradiated specimens. Thermal helium desorption spectrometry was performed to obtain the types of He traps. [ABSTRACT FROM AUTHOR]

In this work, we studied the evolution of vacancy-like defects and the formation of brittle precipitates in a reduced-activation V−Cr−Mn medium-entropy alloy. The evolution of local electronic circumstances around Cr and Mn enrichments, the vacancy defects, and the CrMn3 precipitates were characterized by using scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and positron annihilation spectroscopy. The microstructure measurements showed that the Mn and Cr enrichments in the as-cast sample significantly evolved with temperature, i.e., from 400 °C, the Cr/Mn-segregated regions gradually dissolved into the matrix and then disappeared, and from 900 °C to 1000 °C, they existed as CrMn3 precipitates. The crystallite size of the phase corresponding to CrMn3 precipitates was about 29.4 nm at 900 °C and 43.7 nm at 1000 °C. The positron annihilation lifetime results demonstrated that the vacancies mediated the migration of Cr and Mn, and Cr and Mn segregation finally led to the formation of CrMn3 precipitates. The coincidence Doppler broadening results showed that the characteristic peak moved to the low-momentum direction, due to an increase in the size of the vacancy defects at the interface and the formation of CrMn3 precipitates. [ABSTRACT FROM AUTHOR]

In order to study the microstructural evolution of the He + irradiated FeCrNi model alloy, 140 keV He + ions were implanted into the specimen with the fluence of 1 × 10 15 ions/cm 2 at room temperature. Positron annihilation spectroscopy was used to characterize the evolution of micro defects during isochronal annealing between 423 and 873 K. The decrease of the S parameter between 573 and 623 K has been associated to the annihilation of vacancy clusters, which were not trapped by helium atom. While the decline of the S parameter between 773 and 823 K in the damage region might be caused by the dissociation of He n V m clusters. The dissociated vacancy clusters were unstable and annihilated rapidly, which decreases the concentration of vacancy defects. [ABSTRACT FROM AUTHOR]

The evolution of microstruture for Fe16.7Cr14.5Ni model alloy and 316 stainless steel irradiated with 140 keV He ions were studied by Positron annihilation spectroscopy. The fluences were 1 × 10 16 and 5 × 10 16 He ions/cm 2 . The irradiation temperature was room temperature and 573 K, respectively. The variation of S parameter-incident positron energy profile indicated that large amount of vacancy-type defects formed after He ion irradiation. Meanwhile, helium atoms deposited in bulk and certain amount of He-vacancy complexes were formed. The vacancy-type defects could be the major defects in track region and He-vacancy complexes would be the main defects in cascade region. The vacancy-type defects could migrate and aggregate to form vacancy clusters and even microvoids at elevated temperature irradiation. The diffusion mechanism of helium atoms might be changed at different irradiation temperature. [ABSTRACT FROM AUTHOR]

Microstructure of 9Cr–WVTiN reduced-activation martensitic steels with two different Ti concentrations irradiated with Fe + , He + and H + at 300 °C was studied with transmission electron microscopy. Small dislocation loops were observed in the irradiated steels. The mean size and number density of dislocation loops decreased with the increase of Ti concentration. The segregation of Cr and Fe in carbides was observed in both irradiated steels, and the enrichment of Cr and depletion of Fe were more severe in the low Ti-concentration 9Cr–WVTiN steel. [ABSTRACT FROM AUTHOR]

Irradiation structural damage (e.g., radiation tracks, amorphous layers, and vesicles) is widely observed in lunar soil grains. Previous experiments have revealed that irradiation damage is caused by the injection of solar wind and solar flare energetic particles. In this study, cordierite and gabbro were selected as analogs of shallow and deep excavated lunar crust materials for proton irradiation experiments. The fluence was 1.44 ± 0.03 × 1018 H+/cm2, which is equivalent to 102 years of average solar wind proton implantation on the Moon. Before and after irradiation, structural damage in samples is detected by slow positron annihilation technology (PAT), Doppler broadening (DB) measurement, focused ion beam (FIB), and transmission electron microscopy (TEM). The DB results showed the structural damage peaks of irradiated gabbro and cordierite were located at 40 and 45 nm. Hydrogen diffused to a deeper region and it reached beyond depths of 150 and 136 nm for gabbro and cordierite, respectively. Hydrogen atoms occupied the original vacancy defects and formed vacancy sites—hydrogen atom complexes, which affected the annihilation of positrons with electrons in the vacancy defects. All of the DB results were validated by TEM. This study proves that the positron annihilation technique has an excellent performance in the detection of defects in the whole structure of the sample. In combination with TEM and other detection methods, this technology could be used for the detection of structural damage in extraterrestrial samples. [ABSTRACT FROM AUTHOR]

• Fe 2 AlB 2 samples were exposed to varying He fluences, energy, and temperatures. • Room temperature (RT) irradiation triggers notable changes: a-lattice expands 0.3 %, and c-lattice contracts 0.07 %. • An embedded amorphous layer formed after irradiation at RT. • No cracks are formed after irradiation, making Fe 2 AlB 2 more promising for nuclear application compared to Ti 3 SiC 2 and Ti 2 AlC. Layered carbides and borides, blending ceramic and metallic characteristics, present compelling prospects for future nuclear reactor applications due to their complex nanolaminate crystal structure. To explore the behavior of Fe 2 AlB 2 under different conditions, helium irradiation is conducted across saturation fluences and under different annealing and irradiation temperatures. Room temperature (RT) irradiation causes some changes: a-lattice expands 0.3 %, c-lattice contracts 0.07 %, and an embedded amorphous layer into the matrix is formed. 400 °C annealing keeps an amorphous structure whereas 800 °C annealing fully recrystallizes with bubble growth. Increasing the irradiation temperature to 400 °C with the same fluence, smaller bubbles form without an amorphous layer, indicating defect recombination depends on helium attachment to vacancies. Under irradiation at 700 °C, faceted bubbles develop exclusively within Fe 2 AlB 2 , with no such bubbles in Al 2 O 3. These faceted bubbles align themselves along (110) planes. Simultaneously, irradiation prompts tangled dislocations within the damaged layer, fostering the congregation of polygonal bubbles along grain boundaries (GBs) and creating denuded areas at GBs. Fe 2 AlB 2 demonstrates remarkable oxidation resistance under high-temperature irradiation, maintaining surface stability without the cracks seen in ion-irradiated Ti 3 SiC 2 and Ti 2 AlC at RT. Fe 2 AlB 2 shows promise for use in reactors operating at temperatures above 500 °C due to its resilience to irradiation. Further investigation is warranted for its application in reactors operating in environments exceeding this threshold temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

Microstructural evolution of super-clean reduced-activation martensitic steels irradiated with single-beam (Fe+) and sequential-beam (Fe+ plus He+) at 350°C and 550°C was studied. Sequential-beam irradiation induced smaller size and larger number density of precipitates compared to single-beam irradiation at 350°C. The largest size of cavities was observed after sequential-beam irradiation at 550°C. The segregation of Cr and W and depletion of Fe in carbides were observed, and the maximum depletion of Fe and enrichment of Cr occurred under irradiation at 350°C. [ABSTRACT FROM AUTHOR]

A synergistic effect between the helium and hydrogen elements exists in fusion reactors materials. To explore its microscopic mechanism, this paper meticulously investigates the H and He action for vacancy-like defects in pure Fe and Fe9Cr alloys by using first-principles calculations. The He and H vacancy-like defects were performed within atomistic simulations in body-centered cubic Fe and Fe9Cr alloys. Via analyzing the structures of the clusters, we find that He atoms in the VacHe n H m clusters are more energetically favorable to occupy the center of the vacancy and the H atoms will attach to the free surface. Based on the comprehensive analysis of the vacancy trapping energy, vacancy formation energy, formation volumes, and the electron density maps, He elements play a more dominant role within the H/He synergistic effect, while H elements aggravate the bubble growth. There is no evident chemical bonding between He and H atoms. Concerning the Cr atoms, the Cr-He possesses the strongest repulsive energy within the considered diatomic molecules. The Cr element could weaken the aggregation and reduce the diffusion barriers of the vacancies, thus inhibiting the growth of vacancy-like defects to some extent. These results would help to provide insights into the synergistic effect of He and H for vacancy-like defects in Fe9Cr alloy. [ABSTRACT FROM AUTHOR]

A comprehensive investigation was conducted to explore the impact of helium on dislocation loops in RAFM steel. This was achieved by employing three types of dual-beam irradiations, which include simultaneous dual-beam irradiation with Ar++He+, sequential dual-beam irradiation with Ar+/He+ and He+/Ar+. In addition, single-beam irradiation with Ar+ and He+ were also performed for reference. The irradiation temperature is 723 ± 5 K. The evolutions of dislocation loop were characterized by transmission electron microscopy (TEM). After He+ irradiated to 0.005 dpa, high-density loops with an average size of 4.3 nm were observed. The main mechanism for the formation of the loops at such a low damage dose should be attributed to the process of the ejection of self-interstitial atoms triggered by He clusters. Significantly, in the RAFM steel exposed to Ar++He+ irradiation, the dislocation loops exhibit a significantly larger average size compared to those resulting from Ar+/He+ and He+/Ar+ irradiation. The loop density produced by He+/Ar+is the largest, and the loop density produced by Ar+/He+ is the smallest. The order of the amount of self-interstitial atoms (loops) caused by three types of dual ion beam irradiation is Ar++He+ > He+/Ar+ > Ar+/He+. [ABSTRACT FROM AUTHOR]

• Helium diffusion and desorption behavior was researched by DBS and TDS measurements. • Helium atoms combining with dislocation change the distribution of electron density. • Helium atoms trapped by dislocations form relatively stable complexes. • Dislocations inhibit the helium radiation damage. Suppression of transmutation helium can be achieved by introducing trapping sites such as dislocation and grain boundary in nuclear materials. In order to understand role of dislocations in helium irradiation effect in metal, positron annihilation spectroscopy and thermal desorption measurements were performed to study the interaction of helium atoms with dislocation in deformed Fe-9 wt.Cr alloys irradiated by 10 keV helium ions. The formation of irradiation defects and the thermal stability of helium-defect complexes are discussed. Analyzing the parameters of positron spectrum, the introduced dislocations will change the positron parameters of irradiated samples, which demonstrate that the dislocation has changed normal irradiation effects. Judging from thermal desorption spectrum, we can see the helium desorption peak of the deformed sample is ahead of well-annealed sample. [ABSTRACT FROM AUTHOR]

The evolution of defects with isochronal annealing between 373 and 1273 K in 316L stainless steels, irradiated by helium ions at room temperature (RT), has been studied by the slow positron Doppler broadening spectroscopy (DBS). The results showed that with annealing temperature between RT and 673 K, the S parameters of sample were maintained. It indicates that below 673 K, on the one hand, some vacancies introduced by irradiation were gathered to form vacancy clusters and on the other hand, some vacancies migrated and recovered. From 773 K to 1073 K, there was continuous growth of He n V m cluster, resulting in rapid increasing of S parameter. After 1073 K, unstable He n V m clusters dissociated into vacancies and He atoms. The vacancies were vanished rapidly, which decreases the concentration of vacancy defects, leading to decline of S parameter. [ABSTRACT FROM AUTHOR]

Positron annihilation technology is a nondestructive detection technique to study the microscopic defects in materials. It is well known that the micro defects will redistribute the charge in materials. In this paper, the charge density of helium in iron was calculated by the Vienna Ab initio Simulation Package (VASP) and the positron annihilation parameters were obtained by Doppler program. The results demonstrated that different types of defects in materials will cause a great variety in charge density, which lead to the change of positron annihilation parameters. In a vacancy cluster containing 6 monovacancies, the positron annihilation lifetime decreases rapidly once the number of helium is greater than the number of vacancies. [ABSTRACT FROM AUTHOR]

To provide a basic understanding of the synergy effect of hydrogen and helium on structural materials for future advanced nuclear systems, the vacancy-type defects in SIMP steel induced by separate and sequential H and He implantation at room temperature was investigated using positron annihilation Doppler broadening spectroscopy (DBS) and transmission electron microscopy (TEM). The DBS results indicated that, when implanted by H and He separately, the ΔS parameter of the H-implanted sample was greater than that of He, although the damage level (that is, the displacement per atom) induced by H was lower than that induced by He. This could indicate that He is more easily trapped by vacancy than H and prefers to occupy the center of the vacancy. When sequentially co-implanted by He and H, whatever the implantation sequence, the ΔS parameter was lower than that of H-only implantation. In addition, the ΔS parameter of sequential He + H implantation was greater than that of H + He implantation when the dose of H was sufficiently high. Combined with the TEM results, the synergistic effects of He and H on vacancy-type defect evolution are discussed. [ABSTRACT FROM AUTHOR]

Abstract This study aims to investigate the effects of temperature and dose on the vacancy-defect evolution in 304L stainless steel irradiated by the triple beam of Ni, H, and He ions below 673 K, which is relevant to water-cooled nuclear energy facilities. The irradiation experiments were performed simultaneously using 150-MeV Ni ions whose energy was degraded by passing through a tantalum foil of 8.5-μm thick, 100-keV H ions, and 200-keV He ions at 473, 523, 573, 623, and 673 K, respectively. The irradiation-induced microstructures in the steel were probed by the slow positron beam technique. The results show that the S parameter of the irradiated sample decreases as the temperature increases, and the S parameter of the high-dose irradiated sample decreases further. We explained the results by analyzing the structure of the defects in the irradiated samples at various temperatures and the effects of the annealing effect. In addition, the analysis of the S W plots reveals the transition of the helium-vacancy cluster to the overpressured He m V n (m > n) cluster under the influence of temperature and irradiation dose. [ABSTRACT FROM AUTHOR]

REFERENCE 1 Z. Guo, Y. Zhang, W. Xu, S. Jin, X. Gan, H. Zhang, D. Chen, and Q. Jia, "A von Hamos full-cylindrical spectrometer based on striped Si/Ge crystal for advanced x-ray spectroscopy", Rev. Sci. Instrum. Erratum: "A von Hamos full-cylindrical spectrometer based on striped Si/Ge crystal for advanced x-ray spectroscopy" [Rev. Sci. Instrum. The letter "X" should be lowercase, so the correct name is "Shuoxue Jin.". [Extracted from the article]

The purpose of the study detailed in this paper is to investigate the evolution of microstructural defects in the Fe‐9Cr binary alloy induced by isochronal annealing from 373 to 1223 K. Positron annihilation lifetime spectroscopy (PALS), Doppler broadening spectroscopy (DBS), positron annihilation lifetime calculation, and transmission electron microscope (TEM) are used to analyze and characterize the change of defect concentration, defect type and the micro‐morphology in the Fe‐9Cr alloy as a function of the annealing temperature. The experimental results showed that, a large number of vacancies and dislocations were found to exist in the untreated Fe‐9Cr alloy. The monovacancy (186.2 ps) in the Fe‐9Cr alloy migrated during annealing from room temperature to 573 K. The annealing temperature at 773 K produce aggregation of dislocations and the formation of dislocation networks, as well as their heterogeneous distribution. When the temperature is further increased to 1073 K, most of the vacancies and dislocations are recovered and a bcc‐fcc phase transmition occurred in Fe‐9Cr model alloy. The dislocation density is continuous decreased with the increase of annealing temperature, the recovery is obvious from 773 K annealing to 1073 K annealing in Fe‐9Cr alloy. [ABSTRACT FROM AUTHOR]

Fe-Cu systems, model alloys of nuclear reactor pressure vessel (RPV) steels, heat treatments by annealing and quenching, are studied by the positron annihilation technique and high-resolution SEM. The different effect of annealing and quenching on the formation of Cu precipitates was discussed. The ultrafine Cu precipitates, which are formed in Fe- x wt.% Cu ( x = 1.0 and 1.5) alloys after thermal annealing, are observed clearly and no obvious Cu precipitates were found in the quenched alloys. The annealing temperature has an effect on the concentration of Cu precipitates, which leads to a change of the proportion of positron annihilation in the Cu precipitates, and this can be reflected by the change of the W parameters. Positron annihilation Doppler broadening spectroscopy results show that Cu precipitates formed during annealing at 1173 K still exist when the annealing temperature is higher than 1453 K. SEM measurements were used to observe the size and the distribution of Cu precipitates in the samples, after using different annealing temperature. [ABSTRACT FROM AUTHOR]

Abstract: Si1− x Co x magnetic semiconductors were prepared by implanting 200keV Co ions into p-type Si(100) wafer at room temperature, followed by 600–900°C annealing. Room temperature ferromagnetism was observed in all samples and saturation magnetization was enhanced after 900°C annealing, for which nano-sized (several nm to 50nm) CoSi2 precipitates were present. It was found that the formation of CoSi2 phase could play an important role in the enhancement of ferromagnetism. [Copyright &y& Elsevier]

The nucleation and growth of the helium bubble in the structure material usually were subjected to temperature in a thermodynamic environment. In this study, Y-bearing oxide dispersed strengthened (ODS) ferritic/martensitic steels were used as the research material. The Y-bearing ODS steel samples with a thickness of 30 microns were irradiated successively by helium ions with three energies of 300 keV, 400 keV and 550 keV at room temperature and 450°C respectively. Firstly, the evolution of defects caused by H e + irradiation is analyzed by using slow positron beam Doppler broadening spectroscopy (DBS) in positron annihilation spectroscopy technology (PAS). The formation and growth of helium bubbles are deduced from the changes in the concentration of vacancy-type defects. The increase in the size of the helium bubbles at high temperatures leads to a certain distortion of the crystal lattice, which is also verified by analyzing the grazing incidence X-ray diffraction (GIXRD) patterns. The characterization of radius and concentration of helium bubbles in samples irradiated at room temperature and 450°C have been studied by Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM). The results showed that the intensity (I) ~ q-vector (q) curves of samples vary with irradiation temperature over ranges of 0.13 ≤ q ≤ 4.6 nm−1, which is attributed to the growth of helium bubbles at different irradiation temperature. It is found that the average size of helium bubbles under room temperature irradiation is about 1.78 nm, and the size distribution is narrow, while at the irradiation temperature of 450°C, the size of helium bubbles increases to 2.9 nm, and the size distribution is wider. This result is also verified from the TEM analysis. Besides, the shape of helium bubbles was assumed roughly and tends to spherical with higher temperatures. [ABSTRACT FROM AUTHOR]

To investigate the influence of transmutation rhenium on the irradiation-induced defects in tungsten, H+ and He+ irradiation of 50 keV with a fixed fluence of 1 × 1016 atoms·cm−2 were conducted on W x Re (x =0, 3, 5 and 25 wt.%) alloys, respectively. Doppler Broadening Spectroscopy and Coincidence Doppler Broadening Spectroscopy both based on slow positron beam were employed in the current work to characterize the depth distribution and the chemical surroundings of the irradiation-induced defects. The results showed that under 723K irradiation, Re addition suppressed the accumulation of vacancy-type defects compared with pure W. This suppression was enhanced by increasing Re content in W. An obvious Re-related peak from (7-28) × 10−3 m 0 c was observed in CDB spectra of well-annealed W-Re alloys. The irradiation effect led to the height deviation of Re-related peak. The decrease of the Re-related peak could be attributed to the formation of irradiation-induced defects in irradiated samples, and the reduction of positron annihilation fraction with core electrons of Re. [ABSTRACT FROM AUTHOR]

The spatial relationship between helium bubbles and dislocation loops was observed in detail by TEM in RAFM steel irradiated with 100 keV helium ion to a fluence of 1 × 1021 He+ • m−2 at 723 K. Two families of dislocation loops were observed, with b = ± <010> and b = ± <100>, and habit planes of (010) and (100), respectively. The striking observation is that all of the loops were decorated with helium bubbles. Meanwhile, bubbles are determined to be located inside the loop plane through the investigation using different g -vectors under zone axes of [111], [001] and [011]. [ABSTRACT FROM AUTHOR]

The microstructural evolution of dilute Al–Ag alloys in its early aging stage and at low temperatures ranging from 15 K to 300 K was studied by the combined use of Positron annihilation lifetime spectroscopy (PALS), high resolution transmission electron microscopy (HRTEM), and positron annihilation Coincidence Doppler broadening (CDB) techniques. It is shown that at low temperatures below 200 K, an Ag–vacancy complex is formed in the quenched alloy, and above 200 K, it decomposes into Ag clusters and monovacancies. Experimental and calculation results indicate that Ag clusters in Al–Ag alloys can act as shallow trapping sites, and the positron trapping rate is considerably enhanced by a decreasing measurement temperature. [ABSTRACT FROM AUTHOR]

GaN grown by metal-organic chemical vapour deposition on the sapphire substrate was implanted with 3 MeV Fe10+ ions to fluences of 1 × 1013 to 5 × 1015 ions/cm2 at room temperature. The change of magnetic property with the implantation fluence was measured by vibrating sample magnetometer. The structural features, including implantation-induced interstitials and vacancies, were studied by a combination of Raman spectroscopy, photoluminescence spectroscopy, transmission electron microscopy and positron annihilation technology. The ferromagnetic behaviour was observed in the as-grown sample, and the saturation magnetization reached the maximum after the Fe implantation to a fluence of 5× 1013 ions/cm2. With increasing fluence, it decreased to be even smaller than that of the as-grown sample. The possible reasons are discussed. • Magnetic and structural properties of Fe-implanted GaN were investigated.. • The N vacancies and dislocations can retard the Fe activation at Ga sites. • Defect annealing would improve the saturation magnetization of Fe-implanted GaN. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations have been implemented to investigate the helium trapping effect in multi-vacancies, and the stability and energetics of He n V m complexes (n = 0–6, m = 0–4). The existence of Cr inhibits the capture of helium atoms in multiple vacancies to some extent. A stronger helium self-trapping aggregation than that in pure iron was found in Fe–Cr alloys. In the early stage of nucleation, the He n V m complexes with higher density in Fe–Cr alloys provide more annihilation sites for the irradiation induced recombination of Frankel pairs, and have higher irradiation swelling resistance than pure iron. A new mechanism has been found that the possibility of the formation of helium-vacancy complexes depends on the helium atoms (n) or vacancies (m). Our simulation results corroborate that when the n/m ratio tends to increase, there is spontaneous emission of helium atoms or self-interstitial atoms (SIAs), and it is difficult to grow helium-vacancy-type complexes in Fe–Cr alloys, which provides necessary information for explaining complex experimental phenomena. • The existence of Cr inhibits the capture of helium atoms in multiple vacancies. • A stronger helium self-trapping aggregation was found in Fe–Cr alloys. • Fe–Cr alloys have better irradiation swelling resistance. • It is difficult to grow helium-vacancy-type complexes in Fe–Cr alloys. [ABSTRACT FROM AUTHOR]

The behavior of helium in reduced-activation ferritic/martensitic steels was investigated systematically with positron annihilation Doppler broadening measurement and thermal desorption spectroscopy. Specimens were irradiated with helium ions with different energies to various fluences at different temperatures. A threshold fluence was observed above which the rate of formation and growth of helium bubbles dramatically increased. Irradiation at higher temperature could suppress the formation and growth of HenVm clusters with low binding energies and enhance that of helium bubbles and HenVm clusters with high binding energies. Different changes of S parameters were observed in various depth after the irradiation temperature was increased from 523 K to 723 K. Irradiation of 18 keV-He+ enhanced the growth of HenVm clusters and helium bubbles compared with 100 keV-He+ irradiation. A possible mechanism is discussed. [ABSTRACT FROM AUTHOR]