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Yoshida M., Nishibata I., Matsuda T., et al., Journal of Applied Physics, 132(7), 075101 (2022) https://doi.org/10.1063/5.0083511, This study aims to investigate the influence of the pulse duration on the mechanical properties and dislocation density of an aluminum alloy treated using dry laser peening (DLP), which is a laser peening technique that uses ultrashort pulsed laser-driven shock wave to eliminate the need for a sacrificial overlay under atmospheric conditions. The results of the micro-Vickers hardness test, residual stress measurement, and dislocation density measurement demonstrate that over a pulse duration range of 180 fs to 10 ps, the maximum peening effects are achieved with a pulse duration of 1 ps. Moreover, the most significant DLP effects are obtained by choosing a pulse duration that achieves a laser intensity that simultaneously generates the strongest shock pressure, suppresses optical nonlinear effects, and realizes the least thermal effects, which weaken the shock effects. Shock temperature calculations based on thermodynamic equations also suggest that a laser intensity driving a shock pressure less than 80 GPa, as in the case of a pulse duration of 1 ps in this study, maintains the solid state of the material throughout the process, resulting in significant DLP effects.

Prediction of material performance in fusion reactor environments relies on computational modelling, and will continue to do so until the first generation of fusion power plants come on line and allow long-term behaviour to be observed. In the meantime, the modelling is supported by experiments that attempt to replicate some aspects of the eventual operational conditions. In 2019, a group of leading experts met under the umbrella of the IEA to discuss the current position and ongoing challenges in modelling of fusion materials and how advanced experimental characterisation is aiding model improvement. This review draws from the discussions held during that workshop. Topics covering modelling of irradiation-induced defect production and fundamental properties, gas behaviour, clustering and segregation, defect evolution and interactions are discussed, as well as new and novel multiscale simulation approaches, and the latest efforts to link modelling to experiments through advanced observation and characterisation techniques. MRG, SLD, and DRM acknowledge funding by the RCUK Energy Programme [grant number EP/T012250/1]. Part of this work has been carried out within the framework of the EUROFusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. JRT acknowledges funding from the US Department of Energy (DOE) through grant DE-SC0017899. ZB, LY,BDW, and SJZ acknowledge funding through the US DOE Fusion Energy Sciences grant DE-SC0006661ZB, LY and BDW also were partially supported from the US DOE Office of Science, Office of Fusion Energy Sciences and Office of Advanced Scientific Computing Research through the Scientific Discovery through Advanced Computing (SciDAC) project on Plasma-Surface Interactions. JMa acknowledges support from the US-DOEs Office of Fusion Energy Sciences (US-DOE), project DE-SC0019157. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the US Department of Energy (DOE) under contract DE-AC05-76RL01830. YO and YZ were supported as part of the Energy Dissipation to Defect Evolution (EDDE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under contract number DE-AC05-00OR22725. TS and TT are supported by JSPS KAKENHI Grant Number 19K05338.

A study of high-temperature defect recovery has been carried out for W-5 wt% Ta alloy, irradiated with 2 MeV W+ ions at 500 °C, up to 1.2 dpa. After post-irradiation annealing at 1200 °C for 15 min, the damage microstructure evolved from a random distribution of small loops to a mixture of large loops, dislocation lines and voids. The average size of loops increased by a factor of ∼4, up to 17.7 nm, whereas the number density dropped by an order of magnitude, to ∼5.3 × 1021 m−3. Only loops with b = ½ were observed and they were identified to be exclusively interstitial type. This is in sharp contrast with the presence of ∼25% vacancy type ½ loops in the as-irradiated condition. Voids were formed as a result of accelerated vacancy/vacancy-cluster migration at 1200 °C, achieving an average size of ∼2.5 nm and a high density of ∼5.1 × 1022 m−3. The role of tantalum is discussed. Furthermore, the high-temperature defect recovery in W-5Ta after self-ion (this work) and proton irradiations (Ipatova et al., 2017) are compared, based on which the possible influence of hydrogen upon defect evolution is discussed. Keywords: High-temperature, Defect recovery, Self-ion irradiation, W-5Ta

We succeeded in improving the fatigue properties of friction stir welded 7075-T73 aluminum alloy, e.g., prolonging the fatigue life at lower stress amplitude as compared to the base metal, using femtosecond laser peening, which was performed in air without any overlays such as a protective coating and plasma confinement medium, which are necessary for conventional nanosecond laser peening. The results of the plane bending fatigue tests with a stress ratio of R= -1 demonstrated that femtosecond laser peening enhanced the fatigue strength of the friction stir welded specimen at 106 cycles by approximately 15 MPa compared with that of the base metal, and prolonged the fatigue life of the friction stir welded specimen under cyclic loading at a stress amplitude of 200 MPa by approximately 3.7 times compared with that of the base metal. We suggest that dislocation generation, which occurs behind the shock front under femtosecond-laser-driven shock compression owing to its large shock amplitude, induces surface hardening and compressive residual stresses in a near-surface volume. They prevent the initiation of fatigue cracks on the surface of the specimen, resulting in improved fatigue properties.

High-temperature damage evolution in pure W and W-5Re has been studied by combining transmission electron microscopy and in-situ irradiations with 10 keV He+ ions. The irradiations covered a temperature range of Tirr = 773–1473 K and a fluence range of (4.5–15) × 1019 He+/m2. In pure W, detailed characterizations have shown that damage evolution is highly dependent upon the foil thickness. Regions of thickness

Vacancy diffusion is fundamental to materials science. Hydrogen atoms bind strongly to vacancies and are often believed to retard vacancy diffusion. Here, we use a potential-of-mean-force method to study the diffusion of vacancies in Cu and Pd. We find H atoms, instead of dragging, enhance the diffusivity of vacancies due to a positive hydrogen Gibbs excess at the saddle-point: that is, the migration saddle attracts more H than the vacancy ground state, characterized by an activation excess ΓHm ≈ 1 H, together with also-positive migration activation volume Ωm and activation entropy Sm. Thus, according to the Gibbs adsorption isotherm generalized to the activation path, a higher μH significantly lowers the migration free-energy barrier. This is verified by ab initio grand canonical Monte Carlo simulations and direct molecular dynamics simulations. This trend is believed to be generic for migrating dislocations, grain boundaries, and so on that also have a higher capacity for attracting H atoms due to a positive activation volume at the migration saddles.

Formyl peptide receptor 2 (FPR2) agonists can stimulate resolution of inflammation and may have utility for treatment of diseases caused by chronic inflammation, including heart failure. We report the discovery of a potent and selective FPR2 agonist and its evaluation in a mouse heart failure model. A simple linear urea with moderate agonist activity served as the starting point for optimization. Introduction of a pyrrolidinone core accessed a rigid conformation that produced potent FPR2 and FPR1 agonists. Optimization of lactam substituents led to the discovery of the FPR2 selective agonist 13c, BMS-986235/LAR-1219. In cellular assays 13c inhibited neutrophil chemotaxis and stimulated macrophage phagocytosis, key end points to promote resolution of inflammation. Cardiac structure and functional improvements were observed in a mouse heart failure model following treatment with BMS-986235/LAR-1219.

The purpose of the present study was to verify the effectiveness of dry laser peening (DryLP), which is the peening technique without a sacrificial overlay under atmospheric conditions using femtosecond laser pulses on the mechanical properties such as hardness, residual stress, and fatigue performance. After DryLP treatment of the laser-welded 2024 aluminum alloy, the softened weld metal recovered to the original hardness of base metal, while residual tensile stress in the weld metal and heat-affected zone changed to compressive stresses. The fatigue life almost doubled at a stress amplitude of 180 MPa and increased by a factor of more than 50 at 120 MPa. As a result, DryLP was found to be more effective for improving the fatigue performance of laser-welded aluminum specimens with welding defects at lower stress amplitudes., 本研究の目的は、ドライレーザーピーニング(DryLP)の有効性を検証することである。DryLPは、大気条件下でフェムト秒レーザーパルスを使用して、加工合金中の硬度,残留応力,疲労性能などの機械的特性を改善するピーニング技術である。レーザー溶接された2024アルミニウム合金にDryLP処理を施すと軟化した溶接金属は母材の元の硬度に回復し、溶接金属と熱影響部の残留引張応力は圧縮応力に変わった。疲労寿命は180MPaの引張圧縮試験でほぼ2倍になり、120MPaでは50倍以上増加した。以上から、DryLPは低応力振幅での溶接欠陥のあるレーザー溶接アルミニウム試験片の疲労性能を改善するのにより効果的であることを明らかにした。

We demonstrate the emission of nanometre-sized defect clusters from an isolated displacement cascade formed by irradiation of high-energy self-ions and their subsequent 1-D motion in Au at 50 K, using in situ electron microscopy. The small defect clusters emitted from a displacement cascade exhibited correlated back-and-forth 1-D motion along the [−1 1 0] direction and coalescence which results in their growth and reduction of their mobility. From the analysis of the random 1-D motion, the diffusivity of the small cluster was evaluated. Correlated 1-D motion and coalescence of clusters were understood via elastic interaction between small clusters. These results provide direct experimental evidence of the migration of small defect clusters and defect cascade evolution at low temperature.

To better understand the thermal stability of dislocation loops formed by long-term neutron irradiation in reactor pressure vessel (RPV) steels, in-situ scanning transmission electron microscopy (STEM) observation was performed for a surveillance test specimen of a European pressurized water reactor (PWR). The surveillance test specimen was neutron irradiated to a fluence of 8.2 × 1023 neutrons•m−2. A membrane sample from the surveillance test specimen was annealed at 673 K and 723 K for 30 min using a heating holder, and the same area was in-situ observed under STEM. After annealing, dislocation loops with Burgers vectors of ½ 〈111〉 and 〈100〉 were quantitatively examined. When annealing temperature increased from 673 K to 723 K, the number of dislocation loops decreases, whereas the size of them becomes larger. Correspondingly, the proportion of 〈100〉 dislocation loops changes from 27% to 45%. The ratio of 〈100〉 to ½ 〈111〉 loops increases with annealing temperature rising. The evolution process of dislocation loops during annealing at 723 K was in-situ observed and analyzed to shed light on the transformation mechanism of dislocation loops going from ½ 〈111〉 to 〈100〉. It is the first time to directly observe that two ½ 〈111〉 dislocation loops collide with each other and coalesce to form a 〈100〉 dislocation loop. Moreover, small ½ 〈111〉 dislocation loops could be absorbed by large 〈100〉 dislocation loops, whereas the Burgers vector of 〈100〉 loops remained unchanged. Dislocation decoration occurs during annealing due to the interaction between dislocations and loops. The dislocations decorated by loops are pretty stable during the continuous annealing process, which is well explained by molecular dynamics simulation.

Ascospiroketal B was isolated from a marine-derived fungus as a structurally unique polyketide possessing a rare tricyclic core including 5,5-spiroketal-γ-lactone. An asymmetric total synthesis of ent-ascospiroketal B was achieved using an original synthetic route. The synthesis included the stereoselective construction of 5,5-spiroketal for ascospiroketal B and stereocontrolled construction of a quaternary asymmetric carbon by rearrangement of a trisubstituted epoxide.

Nanocrystalline materials are expected to have improved radiation resistance as the high density of grain boundary area is thought to act as an effective sink for radiation-induced defects. However, continued absorption of defects can alter the structure of grain boundaries and/or enhance their mobility, eventually leading to microstructural degradation in the form of grain coarsening, thus negating their initial radiation tolerance. Hence, an ideal microstructure might be one with a mix of boundaries that are effective sinks and limit grain coarsening. We show through in situ electron irradiation experiments, however, that this is an insufficient condition. Our observations indicate that even a high density of low energy coherent twin boundaries, supposedly stabilizing the microstructure against grain coarsening, can be a detriment in that it biases the mobility of vacancies accumulating during irradiation thereby resulting in preferential void nucleation near twin boundaries. These observations highlight the fact that radiation induced grain boundary migration depends greatly on the topology of the grain boundary network and that the migration of high-angle grain boundaries can be hindered when coordinated at triple junctions composed of at least two low-energy boundaries, e.g., coincidence site lattice boundaries.

Defect microstructures formed in ion-irradiated metals, for example iron or tungsten, often exhibit patterns of spatially ordered nano-scale dislocation loops. We show that such ordered dislocation loop structures may form spontaneously as a result of Brownian motion of loops, biased by the angular-dependent elastic interaction between the loops. Patterns of spatially ordered loops form once the local density of loops produced by ion irradiation exceeds a critical threshold value., 6 pages, 5 figures

The effects of precipitated deuterium, helium, and solute elements on the thermal stability of dislocation loops associated with the glissile motion in the Fe–9Cr–2W ferritic alloy have been studied by in situ TEM observations performed during the post-annealing of the specimens irradiated with the ions of these materials or high-energy electrons. It has been found that dislocation loops formed by helium ion irradiation survive even at higher temperatures, which indicate pinning effects of helium bubbles on dislocation loops. In contrast, the dislocation loops formed by deuterium ion irradiation exhibit 1-D glide motion and disappear at comparatively lower temperatures than those in the case of the loops formed by electrons irradiation. It is suggested that the loops could start to glide owing to reducible effects of precipitated deuterium atoms on the precipitation of alloy elements on the loop dislocations, which was accompanied by the removal of precipitated deuterium from loop dislocations.

Helium bubble production in tungsten has been studied combining transmission electron microscopy and in situ irradiations with 10 keV He+ ions. The irradiations were carried out at four temperatures (773 K, 1073 K, 1273 K, 1473 K), and were held at intervals of (0.45; 0.9; 1.2; 1.5) × 1020 He+/m2 for each temperature. Based on detailed analyses of bubble size, population and spatial distributions, their correlations with irradiation temperature and helium fluence were established. Helium-to-vacancy ratios were also deduced from these data. During high temperature equilibrium, the ratio was close to 3.

The dynamic behaviour of atomic-size disarrangements of atoms—point defects (self-interstitial atoms (SIAs) and vacancies)—often governs the macroscopic properties of crystalline materials. However, the dynamics of SIAs have not been fully uncovered because of their rapid migration. Using a combination of high-voltage transmission electron microscopy and exhaustive kinetic Monte Carlo simulations, we determine the dynamics of the rapidly migrating SIAs from the formation process of the nanoscale SIA clusters in tungsten as a typical body-centred cubic (BCC) structure metal under the constant-rate production of both types of point defects with high-energy electron irradiation, which must reflect the dynamics of individual SIAs. We reveal that the migration dimension of SIAs is not three-dimensional (3D) but one-dimensional (1D). This result overturns the long-standing and well-accepted view of SIAs in BCC metals and supports recent results obtained by ab-initio simulations. The SIA dynamics clarified here will be one of the key factors to accurately predict the lifetimes of nuclear fission and fusion materials.

The rate equation approach is useful for semi-quantitatively simulating long-term processes of accumulation or recovery of lattice defects in crystalline materials upon irradiation or annealing. This approach has been developed and applied to a large number of systems, including 3D or 1D migrating self-interstitial atoms (SIAs) and 1D migrating SIA clusters. The dimensionality of the migration of mobile species significantly affects the forms of the reaction rate. For reactions related to 1D migrating SIAs and clusters, only their reactions with stationary traps have been considered. However, the reactions between 1D migrating SIAs (or clusters) cannot be ignored, especially for processes in metals, in which the most stable configuration of an SIA is the crowdion, under electron and ion irradiations at comparatively high dose rate. In the present study, we use the object kinetic Monte Carlo (KMC) method to find the approximate form of the reaction rate between 1D migrating SIAs. For this purpose, we exami...

Hydroxyapatite materials are potentially useful for biomedical application, especially as vehicles for functional molecules. Structural control of bulk apatite materials, such as in the fabrication of hollow microspheres or porous structures, has been studied for this purpose. However, control of the internal structure of the source apatite crystal itself is still a challenge. Here, we show that small organic molecules incorporated in apatite crystals act as porogens which control the porous structure of apatite single crystal. The presence of amino acid under apatite synthesis conditions leads to firm bindings and encapsulation of the amino acid in apatite single crystals. Amino acid elimination by heating or electron beam irradiation enhances the pore formation in apatite single crystal. Moreover, incorporation of an acidic amino acid in apatite induces peapod like nanotubes in apatite single crystals. This study suggests the potential of using small organics for nano-structural control of apatite single crystals which would be valuable for enhancing drug loadings or modulating material digestion in vivo .

The effect of the crystalline quality of ultrathin Co films on perpendicular exchange bias (PEB) has been investigated using a Au/Co/Au/α-Cr 2 O 3 thin film grown on a Ag-buffered Si(1 1 1) substrate. Our investigation is based on the effect of the Au spacer layer on the crystalline quality of the Co layer and the resultant changes in PEB. An α-Cr 2 O 3 (0 0 0 1)layer is fabricated by the thermal oxidization of a Cr(1 1 0) thin film. The structural properties of the α-Cr 2 O 3 (0 0 0 1) layer including the cross-sectional structure, lattice parameters, and valence state have been investigated. The fabricated α-Cr 2 O 3 (0 0 0 1) layer contains twin domains and has slightly smaller lattice parametersthan those of bulk-Cr 2 O 3 . The valence state of the Cr 2 O 3 (0 0 0 1) layer is similar to that of bulk Cr 2 O 3 . The ultrathin Co film directly grown on the α-Cr 2 O 3 (0 0 0 1) deposited by an e-beam evaporator is polycrystalline. The insertion of a Au spacer layer with a thickness below 0.5 nm improves the crystalline quality of Co, probably resulting in hcp-Co(0 0 0 1). Perpendicular magnetic anisotropy (PMA) appears below the Neel temperature of Cr 2 O 3 for all the investigated films. Although the PMA appears independently of the crystallinequality of Co, PEB is affected by the crystalline quality of Co. For the polycrystalline Co film, PEB is low, however, a high PEB is observed for the Co films whose in-plane atom arrangement is identical to that of Cr 3+ in Cr 2 O 3 (0 0 0 1). The results are qualitatively discussed on the basis of the direct exchange coupling between Cr and Co at the interface as the dominant coupling mechanism.

The activation energy for the long-range intrinsic migration of self-interstitial atoms (SIAs) in metals, , is an important physical quantity closely associated with microstructural evolution upon energetic particle irradiation. The values for various metals have been widely investigated through recovery experiments on specimens irradiated at low temperatures upon thermal annealing, and the values have been estimated from the dependence of measured quantities of the specimens on the annealing temperature. On the other hand, the dependence of measured quantities on irradiation temperature is also expected to reflect the values. It is of importance to compare the values obtained by these two different kinds of experiments. However, no systematic studies have been carried out along the latter line. In this study, the number densities of SIA clusters formed in tungsten upon high-energy electron irradiation are directly measured as a function of the irradiation temperature using high-voltage electron microscop...

The dynamic behavior of nanoscale prismatic dislocation loops can significantly affect the microstructural variation in crystalline materials upon processes such as plastic deformation and high-energy particle irradiation. Using in situ transmission electron microscopy, this study experimentally demonstrates a reaction which follows the collision between two loops with different Burgers vectors in α-iron. Even after the formation of the junction, the reaction progresses further, unlike conventional reactions between dislocations of macroscopic length, and the larger loop finally absorbs the smaller one.

In this study, electron-irradiation-induced phase transformations between alumina polymorphs were investigated by high-resolution transmission electron microscopy. It was found that the electron-irradiation-induced α → κ′ phase transformation occurred in the alumina under 100 keV electron irradiation. It is likely that the knock-on collision between incident electrons and Al3+ cations is responsible for the occurrence of electron-irradiation-induced phase transformation from α-alumina to κ′-alumina.

The effect of platinum on the electron-irradiation-induced decomposition of sapphire was investigated by in situ transmission electron microscopy. Comparison between the decomposition rates of pure sapphire and Pt-deposited sapphire revealed that the deposition of Pt considerably decreased the decomposition rate of sapphire under electron irradiation. These finds suggest Pt suppresses the interatomic Auger decay that occurs between Al3+ and O2− ions, thereby decreasing the decomposition rate of sapphire.

Dynamic interaction of helium bubble with cascade damage in Fe–9Cr ferritic alloy has been studied using in situ irradiation and electron microscopy. During the irradiation of the alloy by 400 keV Fe + ions at temperatures where no thermal motion takes place, induced displacement of small helium bubbles was observed: the bubbles underwent sporadic and instant displacement. The displacement was of the order of a few nanometers. The experimentally determined displacement probability of helium bubbles is consistent with the calculated probability of their dynamic interaction with sub-cascades introduced by the irradiation. Furthermore, during the irradiation of the alloy at higher temperatures, both retarded and accelerated Brownian type motions were observed. These results are discussed on the basis of dynamic interaction of helium bubbles with point defects that survive through high-energy self-ion irradiation.

Brownian-type motion of helium bubbles in aluminum and its dynamical response to irradiation with 100-keV Al+ ions at high temperatures has been studied using in situ irradiation and transmission electron microscopy. It is found that, for most bubbles, the Brownian-type motion is retarded under irradiation, while the mobility returns when the irradiation is stopped. In contrast, under irradiation, a small number of bubbles display exceptionally rapid motion associated with the change in bubble size. These effects are discussed in terms of the dynamical interaction of helium bubbles with cascade damage formed by the high-energy self-ion irradiation.

We report the calibration of a rate theory numerical code capable to reproduce the agglomeration of point-defects produced in α-iron by irradiation under cascade damage conditions. The input parameters are obtained by performing transmission electron microscopy (TEM) experiments in α-iron. It was irradiated at temperatures between 200 and 400 °C with high flux krypton ion under resolvable point-defect cluster conditions. The TEM analyse of the sample irradiated at the highest temperature reveals the presence of two dislocation loop populations: large ones are decorated with small ones, both vacancy and interstitial in type. The vacancy loops are proposal to be located in the compressive side of the large interstitial loops.

Dislocations are ubiquitous linear defects and are responsible for many of the properties of crystalline materials. Studies on the glide process of dislocations in bulk materials have mostly focused on the response of dislocations with macroscopic lengths to external loading or unloading. Using in situ transmission electron microscopy, we show that nanometer-sized loops with a Burgers vector of ½〈111〉 in α-Fe can undergo one-dimensional diffusion even in the absence of stresses that are effective in driving the loops. The loop size dependence of the loop diffusivity obtained is explained by the stochastic thermal fluctuation in the numbers of double kinks.

Dynamical interaction of helium bubbles with grain boundaries in Fe and Fe–9Cr has been studied by in situ electron microscopy and thermal desorption spectroscopy (TDS). It is clearly demonstrated that most small helium bubbles are swept to the specimen surface by dynamical interaction with the moving grain boundaries during re-crystallization, which induces easy motion along the boundary. At small angle grain boundaries, helium bubbles are frequently trapped at grain boundary dislocations and move along the dislocation line. The bubble diffusivity along the grain boundary dislocation is statistically estimated from the moving path and the value is similar to or a little higher than that in the matrix. Well correlated and enhanced thermal desorption spectra with the sweeping of helium bubbles by moving grain boundaries in Fe and Fe–9Cr are revealed.

Effects of cascade damage on the behavior of helium bubbles in copper have been studied. To examine the dynamical response of the helium bubbles to irradiation with high energy self ions, in situ TEM observations during irradiation with 400 keV Cu + at room temperature and 830 K were carried out. Intermittent motion of bubbles of a few nm was observed at room temperature where the bubble was thermally immobile. At high temperature, in addition to Brownian type motions, rapid motion of rather long distances of about 10 nm was observed. The detailed analysis of the frequency and distance of these motions suggested the direct interaction of helium bubbles with sub-cascades and secondary defects.

Transmission electron microscopy of high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications (500–1200 °C). Bulk isochronal and isothermal annealing of ion irradiated pure tungsten (2 MeV W+ ions, 500 °C, 1014 W+/cm2) with temperatures of 800, 950, 1100 and 1400 °C, from 0.5 to 8 h, was followed by ex situ characterisation of defect size, number density, Burgers vector and nature. Loops with diameters larger than 2–3 nm were considered for detailed analysis, among which all loops had b = 1 2 〈 1 1 1 〉 and were predominantly of interstitial nature. In situ annealing experiments from 300 up to 1200 °C were also carried out, including dynamic temperature ramp-ups. These confirmed an acceleration of loop loss above 900 °C. At different temperatures within this range, dislocations exhibited behaviour such as initial isolated loop hopping followed by large-scale rearrangements into loop chains, coalescence and finally line–loop interactions and widespread absorption by free-surfaces at increasing temperatures. An activation energy for the annealing of dislocation length was derived, finding E a = 1.34 ± 0.2 eV for the 700–1100 °C range.

Extensive simulations based on classical molecular dynamics have shown that small interstitial-type perfect dislocation loops in various metals and alloys have the structure of bundles of crowdions and a loop can easily makes the one-dimensional glide motion due to almost independent motion of crowdions in the loop. However, the experimental knowledge on the motion of loops is not enough. The present study dynamically examined the motion process of loops in pure iron under 1000 keV electron irradiation and thermal annealing by using transmission electron microscopy under which loops could move. Two types of loops were formed by irradiation. Loops of one type possessed the Burgers vector of 1/2 and the habit plane of {011}, and loops of the other type were {001}. Loops of the former type made back-andforth glide motion and expansion towards the direction along their Burgers vectors when they were smaller than about a few-ten nanometers in diameter. This strongly suggests that these small 1/2 loops have the structure of the bundle of crowdions. Loops of the latter type only rarely moved less frequently when they were smaller than about the same size. When loops of two types grew larger than about 50 nm, the characteristics of the motion of loops changed drastically. Dislocation segments of each large loop made long-distance glide independently of their opposite segments, and the habit plane deviated from the original ones. This kind of motion means that selfinterstitial atoms at the central region of such large loops are no longer the crowdions.

Surface hardening of Ni-based self-fluxing alloy was carried out using plasma-carburization. The carburization was performed utilizing methane glow discharge plasma on sintered Ni-based self-fluxing alloy (METCO 16C) at 977 °C and 1065 °C for 3.6 ks. The carburized surfaces were characterized by employing optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy and Vickers micro-hardness testing. The SEM and EPMA micrographs show that the thickness of the carburized hard layer increased with increasing temperature, to a depth of approximately 120–200 μm. Hard chromium carbide (Cr 3 C 2 ) was found to precipitate near the surface on carburization at 977 °C more than at 1065 °C. Cr 3 C 2 contributes to the surface hardening.

The one-dimensional motion of interstitial-type dislocation loops in Fe–9Cr ferritic alloy is studied by in situ transmission electron microscopy. Loop motion is examined under 1000 kV high-energy electron irradiation at temperatures ranging from 110 to 680 K and under thermal annealing from 295 to 960 K without introduction of additional displacement subsequent to the irradiation at 110 K. The results are compared with those in pure bcc Fe, and the effects of Cr on the motion of loops are extracted. Under high-energy electron irradiation, the motion frequency of loops is only slightly reduced by Cr. In contrast, under annealing, the motion frequency of loops in Fe–9Cr is significantly reduced by Cr. The origins of such two-way effects of Cr on the motion frequency of loops are discussed.

Thermal desorption of helium from Fe–9Cr and pure Fe which were irradiated with 5 keV He + ions at 85 or 473 K have been studied by thermal desorption spectrometry (TDS) at temperatures from room temperature to 1270 K and related microstructure changes by TEM. It is found that five TDS peaks appear in Fe–9Cr specimen and these peaks are well correlated with microstructure changes. From these results, the five peaks I Cr , II Cr , III Cr , IV Cr and V Cr may be attributed to release of trapped helium atoms by the break-up of vacancy–helium–self-interstitial atom complexes or very tiny loops, glide to the specimen surface or coalescence of interstitial type dislocation loops, shrinkage of dislocation loops, bubble migration to the specimen surface and α–γ phase transformation, respectively. Precipitation of Cr around the loops and bubbles in Fe–9Cr is revealed by STEM-EELS and this could shift the related TDS peaks to higher temperatures.

Thin foil of fcc and bcc metals subjected to tensile deformation has been found to exhibit an anomalously high density of small vacancy clusters, probably in the absence of dislocations. Deformation of fcc Au and bcc Fe containing pre-introduced He bubbles is carried out, at strain rates ranging from 10 −3 to 10 5 s −1 to a 10 2 % strain at −180 and 25 °C. Microstructures in the deformed regions are examined by transmission electron microscopy. Rows of bubbles are formed due to extreme elongation of bubbles under stress and its subsequent division into smaller pieces in response to vacancy diffusion around the bubble surfaces. The bubble rows are parallel to the low-index crystallographic directions, 〈001〉, 〈011〉, and 〈012〉 for Au and 〈011〉 and 〈001〉 for Fe, which can be resolved into ‘slip directions’. The results indicate that displacement of atoms in these thin-foil specimens during tensile deformation progresses while conforming to the nature of the crystal, even in the absence of dislocations.

The dynamical response of helium bubbles to irradiation with high energy self-ions in pure Cu has been studied by in situ electron microscopy. At enough high temperature, Brownian type motion of helium bubbles in the matrix and their easy motion along the edge dislocation are observed. At low temperatures where bubbles are thermally immobile, it is found that intermittent motion of the bubble is induced along interstitial type dislocation loops that are growing or shrinking under the irradiation. Possible mechanisms for the intermittent motion under the irradiation are discussed.

Formation processes and characteristics of platelet-like extended defects in FZ Si under the irradiation with low-energy H+ ions are examined, and the results are compared with those from He+ ion and high-energy electron irradiation. Silicon discs with (0 1 1) surfaces are irradiated by 5 keV H+, 10 keV He+ ions between 570 and 870 K, and by 1000 keV electrons between 470 and 670 K. It is considered from the temperature dependence of the characteristics of extended defects induced by H+ ion irradiation, that the interaction between self-interstitial atoms and hydrogen becomes weak above 770 K. The formation of {1 1 3} interstitial-type defects is enhanced by hydrogen and helium, and the degree is stronger for hydrogen. It is concluded from the difference between aspect ratios of {1 1 3} defects induced by the irradiation with both kinds of ions, that the mechanism for the enhancement by hydrogen is different from that by helium.

Formation and migration of helium bubbles in high purity Fe and an Fe–9Cr ferritic alloy have been studied by in situ electron microscopy and scanning transmission electron microscope–electron energy loss spectrometry (STEM–EELS) analysis. The swelling under irradiation with 10 keV He + ions in the ferritic alloy was retarded in the low fluence region at 400 °C and was reduced at 600 °C even under heavy irradiation. These results suggest trapping effects of vacancies by Cr and its modulation with helium atoms in the bubble formation. Furthermore, it is found that the mean square of the bubble migration distance in both materials is proportional to time, which is a quantitative evidence of Brownian type motion and yields lower diffusivities of the bubbles in Fe–9Cr than in Fe. The retardation of the bubble mobility in Fe–9Cr should be caused by Cr segregation on the bubble surface which was revealed by STEM–EELS analysis.

Formation processes of interstitial-type dislocation loops (I loops) in high-purity Fe under irradiations with 5 keV H+ ions or 1000 keV electrons are examined by in situ transmission electron microscopy at temperatures below room temperature, and the results are compared with that obtained under He+ ion irradiation. For the electron irradiation, conventional model of I-loop nucleation based on the assumption that di-interstitial atoms are stable nuclei of I loops is questioned. The volume density of I loops by H+ ion irradiation is one-order of magnitude higher than that by electron irradiation, and several times lower than that by He+ ion irradiation. The temperature dependence of the volume density of I loops by H+ ion irradiation supports the idea that such enhancement of I-loop formation is due to trapping of self-interstitial atoms by gas atom-vacancy complexes.