Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions

Polycrystalline tungsten（W）and molybdenum（Mo）materials both non-annealed and annealed at temperatures of 800-1750~C have been irradiated with low-energy（220 eV）,high-flux（~10^（21）ions/m^2.s）He~＋at an irradiation temperature of 600℃and at a dose of1.0×10^（25）ions/m^2.This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials.A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He＋dose of 1.0×10^（25）ions/m^2.Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W.Compared to W,Mo suffered much less surface damage after being irradiated at various He~＋doses.

Multiscale modelling of irradiation damage behavior in high entropy alloys

The increasingly harsh environment of the nuclear reactors and the insurmountableflaws of in-service materials have created an urgent need for the development of the brand-new alloys.For last decade,the high-entropy alloys(HEAs),a novel composition-design strategy,have received much attention due to their promise for the nuclearfields.The application of the multiscale modelling is to explore the irradiation performance and underlying mechanisms of HEAs.Abundant results and data deepen the understanding of the irradiation response,and accelerate the development of advanced irradiation-resistant HEAs.This review introduces the state-of-art multiscale modelling used for studying the irradiated properties of HEAs.Representative irradiation-induced microstructures and properties,as well as damage,are summarized.By strengthening the application of multiscale modelling,a rational design of high irradiation-resistant HEAs is expected.

Ar（12+）Induced Irradiation Damage in Bulk Metallic Glass(Cu47Zr45Al8)98.5Y1.5

The highly charged ion Ar^12＋ with an energy of 3 Me V is used for irradiating metallic glass （Cu47Zr45Al8）98.5Y1.5 and polycrystalline metallic W at the irradiation fluences of 1× 10^14 ions/cm2, 1 × 10^15 ions/cm^2 and 1 × 10^16 ions/cm^2. The main structure of metallic glass remains an amorphous phase under different irradiation fluences according to x-ray diffraction analysis. The scanning electron microscope observation on the morphologies indicates that no significant irradiation damage occurs on the surface and cross section of the metallic glass sample after different fluences of irradiation, while a large area of irregular cracks and holes were observed on the surface of metallic W at a fluence of 1 ×10^16 ions/cm^2, with cracks and channel impairments at a certain depth from the surface. The root-mean-square （rms） roughness of metallic glass increases with increasing fluence of Ar^12＋, while the reflectance decreases with increasing irradiation fluence. A nano-hardness test shows that the hardness of metallic glass decreases after irradiation. Under certain a higher capability of resistance to Ar^12＋ irradiation in conditions, metallic glass （Cu47 Zr45Al8 ）98.5 Y1.5 exhibits comparison with polycrystalline W.

Extended damage range of(Al0.3Cr0.2Fe0.2Ni0.3)3O4 high entropy oxide films induced by surface irradiation

Irradiation makes structural materials of nuclear reactors degraded and failed.However,the damage process of materials induced by irradiation is not fully elucidated,mostly because the charged particles only bombarded the surface of the materials(within a few microns).In this work,we investigated the effects of surface irradiation on the indirect irradiation region of the(Al0.3Cr0.2Fe0.2Ni0.3)3O4 high entropy oxide(HEO)films in detail by plasma surface interaction.The results show that the damage induced by surface irradiation significantly extends to the indirect irradiation region of HEO film where the helium bubbles,dislocations,phase transformation,and the nickel oxide segregation were observed.

Atomic simulations of primary irradiation damage in U–Mo–Xe system

To shed a light on Xe bubble nucleation in U–Mo fuel from the view of primary irradiation damage,a reported U–Mo–Xe potential under the framework of embedded atom method has been modified within the range of short and intermediate atomic distance.The modified potential can better describe the interactions between energetic particles,and can accurately reproduce the threshold displacement energy surface calculated by the first-principles method.Then,molecular dynamics simulations of primary irradiation damage in U–Mo–Xe system have been conducted under different contents.The raise of Xe concentration brings about a remarkable promotion in residual defect quantity and generates bubbles in more overpressured state,which suggests an acceleration of irradiation damage under the accumulation of the fission gas.Meanwhile,the addition of Mo considerably reduces the residual defect count and hinders irradiation-induced Xe diffusion especially at high contents of Xe,corroborating the importance of high Mo content in mitigation of irradiation damage and swelling behavior in U–Mo fuel.In particular,the variation of irradiation damage with respect to contents suggests a necessity of taking into account the influence of local components on defect evolution in mesoscale simulations.

Effect of Same-dose Single or Dual Field Irradiation on Damage to Miniature Pig Parotid Glands

Aim To evaluate the effect of single or dual field irra- diation （IR） with the same dose on damage to miniature pig parotid glands. Methodology Sixteen miniature pigs were divided into two IR groups （n=6） and a control group （n=4）. The irradi- ation groups were subjected to 20 Gy X-radiation to one parotid gland using single-field or dual-field modality by linear accelerator. The dose-volume distributions between two IR groups were compared. Saliva from parotid glands and blood were collected at 0, 4, 8 and 16 weeks after irradiation. Parotid glands were removed at 16 weeks to evaluate tissue morphology.Results The irradiation dose volume distributions were significantly different between single and dual field irradi- ation groups （t----4.177, P=0.002）, although dose volume histogramin （DVH） indicated the equal maximal dose in parotid glands. Saliva flow rates from IR side decreased dramatically at all time points in IR groups, especially in dual field irradiation group. The radiation caused changes of white blood cell count in blood, lactate dehydrogenase and amylase in serum, calcium, potassium and amylase in saliva. Morphologically, more severe radiation damage was found in irradiated parotid glands from dual field irradi- ation group than that from single field irradiation group. Conclusion Data from this large animal model demons- trated that the radiation damage from the dual field irradiation was more severe than that of the single field irradiation at the same dose, suggesting that dose-volume distribution is an important factor in evaluation of the radiobiology of parotid glands.

Recent progress on advanced transmission electron microscopy characterization for halide perovskite semiconductors

Halide perovskites are strategically important in the field of energy materials. Along with the rapid development of the materials and related devices, there is an urgent need to understand the structure–property relationship from nanoscale to atomic scale. Much effort has been made in the past few years to overcome the difficulty of imaging limited by electron dose,and to further extend the investigation towards operando conditions. This review is dedicated to recent studies of advanced transmission electron microscopy(TEM) characterizations for halide perovskites. The irradiation damage caused by the interaction of electron beams and perovskites under conventional imaging conditions are first summarized and discussed. Low-dose TEM is then discussed, including electron diffraction and emerging techniques for high-resolution TEM(HRTEM) imaging. Atomic-resolution imaging, defects identification and chemical mapping on halide perovskites are reviewed. Cryo-TEM for halide perovskites is discussed, since it can readily suppress irradiation damage and has been rapidly developed in the past few years. Finally, the applications of in-situ TEM in the degradation study of perovskites under environmental conditions such as heating,biasing, light illumination and humidity are reviewed. More applications of emerging TEM characterizations are foreseen in the coming future, unveiling the structural origin of halide perovskite’s unique properties and degradation mechanism under operando conditions, so to assist the design of a more efficient and robust energy material.

Mechanical properties of self-irradiated single-crystal copper

Molecular dynamics simulations are performed to investigate the influence of irradiation damage on the mechanical properties of copper. In the simulation, the energy of primary knocked-on atoms （PKAs） ranges from 1 to 10 keV, and the results indicate that the number of point defects （vacancies and interstitials） increases linearly with the PKA energy. We choose three kinds of simulation samples： un-irradiated and irradiated samples, and comparison samples. The un-irradiated samples are defect-free, while irradiation induces vacancies and interstitials in the irradiated samples. It is found that due to the presence of the irradiation-induced defects, the compressive Young modulus of the single-crystal Cu increases, while the tensile Young modulus decreases, and that both the tensile and compressive yield stresses experience a dramatic decrease. To analyze the effects of vacancies and interstitials independently, the mechanical properties of the comparison samples, which only contain randomly distributed vacancies, are investigated. The results indicate that the vacancies are responsible for the change of Young modulus, while the interstitials determine the yield strain.

Difference in electron-and gamma-irradiation effects on output characteristic of color CMOS digital image sensors

Changes of the average brightness and non-uniformity of dark output images,and quality of pictures captured under natural lighting for the color CMOS digital image sensorsirradiated at different electron doses have been studied in comparison to those from theγ-irradiated sensors. For the electron-irradiated sensors, the non-uniformity increases obviouslyand a small bright region on the dark image appears at the dose of 0.4 kGy. The average brightnessincreases at 0.4 kGy, increases sharply at 0.5 kGy. The picture is very blurry only at 0.6 kGy,showing the sensor undergoes severe performance degradation. Electron radiation damage is much moresevere than γ radiation damage for the CMOS image sensors. A possible explanation is presented inthis paper.

Effect of helium implantation on SiC and graphite

Effects of helium implantation on silicon carbide（SiC） and graphite were studied to reveal the possibility of SiC replacing graphite as plasma facing materials. Pressureless sintered SiC and graphite SMF-800 were implanted with He＋ions of 20 ke V and 100 ke V at different temperatures and different fluences. The He^＋ irradiation induced microstructure changes were studied by field-emission scanning electron microscopy（FESEM）, atomic force microscopy（AFM）, and transmission electron microscopy（TEM）.

Molecular dynamics simulations of displacement cascades in Fe-10%Cr systems

Molecular dynamics simulations of the displacement cascades in Fe 10%Cr systems are used to sinmlate the primary knocked-on atom events of the irradiation damage at temperatures 300, 600, and 750 K with primary knockedon atom energies between 1 and 15 keV. The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade. During the cascade, all recoil Fe and Cr atoms combine with each other to form Fe Cr or Fe Fe interstitial dumbbells as well as interstitial clusters. The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature. A few large clusters consist of a large number of lee interstitials with a few Cr atoms, the rest are lee Cr clusters with small and medium sizes. The interstitial dumbbells of Fe lee and Fe-Cr are in the （111）and （110） series directions, respectively.

Structural Characterization of Nickel-Base Alloy C-276 Irradiated with Ar Ions

The irradiation damage in nickel-base alloy C-276 irradiated with 115 keV Ar ions from low to very high doses was investigated. Structural characterization was performed using transmission electron microscopy （TEM）, grazing incident X-ray diffraction （GIXRD） and atomic force microscopy （AFM）. High density of interstitial type dislocation loops could be observed at a dose level of around 2.75 displacements per atom （dpa）. With the irradiation dose increased to 27.5 dpa, the average size of loops increased from 5 nm to 16 nm, while the density of the loops decreased from 1.4 × 1011/cm2 to 4.6 × 1010/cm2. When the irradiation dose reached 82.5 dpa, original grains were transformed into subgrains whose sizes observed from TEM were about 20-60 nm. The fragmentation of grains was confirmed by GIXRD. The mean subgrain size was 40 nm, which was obtained from the full width at half maximum （FWHM） of the X-ray diffraction lines using the Scherrer formula and Williamson formula. AFM micrographs showed that nanometer-sized hillocks formed at the dose of 82.5 dpa, which provided further evidence of grain fragmentation at a high irradiation dose.

The irradiation variation of amorphous alloy FeSiB using for fusion devices induced by 2 MeV He ions

Because of its unique long range disordered structure and numerous free volume,amorphous alloy is considered to be able to accommodate the damage caused by ion bombardment and has good irradiation resistance.2 MeV He+ions were selected to irradiate amorphous alloy Fe80Si7B13,and it was found that the arrangement of atoms in the amorphous alloy became uneven.In the bubble layer located near the He ion range which was about 3.5μm from the surface,the local atoms had a tendency of ordered arrangement.Under the irradiation,no obvious damage could be observed on the surface of the amorphous alloy,while the surface roughness increased,which reduced the surface relative reflectivity of the amorphous alloy.After the irradiation,the Fe-based amorphous alloy maintained the soft magnetic performance.The variation of atomic arrangement in the amorphous alloy enhanced its saturation magnetic induction intensity.

Effects of Si^3＋ and H＋ Irradiation Friction on Tungsten Evaluated by Internal Method

Effects of Si^3＋ and H＋ irradiation on tungsten were investigated by internal friction （IF） technique. Scanning electron microscope （SEM） analysis revealed that sequential dual Si＋H irradiation resulted in more serious damage than single Si irradiation. After irradiation, the IF background was significantly enhanced. Besides, two obvious IF peaks were initially found in tem- perature range of 70～330 K in the sequential Si＋H irradiated tungsten sample. The mechanism of increased IF background for the irradiated samples was suggested to originate from the high density dislocations induced by ion irradiation. On the other hand, the relaxation peak PL and non-relaxation peak PH in the Si＋H irradiated sample were ascribed to the interaction process of hydrogen atoms with mobile dislocations and transient processes of hydrogen redistribution, respectively. The obtained experimental results verified the high sensitivity of IF method on the irradiation damage behaviors in nuclear materials.

Irradiation effect of yttria-stabilized zirconia by high dose dual ion beam irradiation

Yttria-stabilized zirconia （YSZ） is irradiated with 2.0-MeV Au2＋ ions and 30-keV He＋ ions. Three types of He, Au, Au ＋ He （successively） ion irradiation are performed. The maximum damage level of a sequential dual ion beam implanted sample is smaller than single Au ion implanted sample. A comparable volume swelling is found in a sequential dual ion beam irradiated sample and it is also found in a single Au ion implanted sample. Both effects can be explained by the partial reorganization of the dislocation network into weakly damaged regions in the dual ion beam implanted YSZ. A vacancy-assisted helium trapping/diffusion mechanism in the dual ion beam irradiated condition is discussed. No phase transformation or amorphization behavior happens in all types of ion irradiated YSZ.

MEASUREMENT OF VACANCY MIGRATION ENERGY BY ELECTRON IRRADIATION

A method together with a new formula were developed for measuring the vacancy migration energy on HVEM considering the effect of surface sink of specimen on point defects.The va- cancy migration energy may be calculated through the loop growth rate under electron irradiation at various temperatures.

Impact of high dose Kr^+ ion irradiation on the corrosion behavior and microstructure of Zircaloy-4

In order to investigate the ion irradiation effect on the corrosion behavior and microstructure of Zircaloy-4, the Zircaloy-4 film were prepared by electron beam deposition on the Zircaloy-4 specimen surface and irradiated by Kr ions using an accelerator at an energy of 300 keV with the dose from 1×1015 to 3×1016ions/cm2. The post-irradiation corrosion tests were conducted to rank the corrosion resistance of the resulting specimens by potentiodynamic polarization curve measurements in a 0.5 mol/L H2SO4 water so- lution at room temperature. Transmission electron microscopy (TEM) was employed to examine the microstructural change in the surface. The potentiodynamic tests show that with the irradiation dose increasing, the passive current density, closely related to the surface corrosion resistance, decreases firstly and increases subsequently. The mechanism of the corrosion behavior transformation is due to the amorphous phase formation firstly and the amorphous phase destruction and the polycrystalline structure formation in the irradiated surface subsequently.

Building metallurgical bonding interfaces in an immiscible Mo/Cu system by irradiation damage alloying (IDA)

For the immiscible Mo/Cu system with a positive heat of mixing （△Hm 〉 0）, building metallurgical bonding interfaces directly between immiscible Mo and Cu and preparing Mo/Cu laminar metal matrix composites （LMMCs） are very difficult. To solve the problem, a new alloying method for immiscible systems, which is named as irradiation damage alloying （IDA）, is presented in this paper. The IDA primarily consists of three steps. Firstly, Mo is damaged by irradiation with multi-energy （186, 62 keV） Cu ion beams at a dose of 2× 1017 ions/cm2. Secondly, Cu layers are superimposed on the surfaces of the irradiation-damaged Mo to obtain Mo]Cu laminated specimens. Thirdly, the irradiation damage induces the diffusion alloying between Mo and Cu when the laminated specimens are annealed at 950 ℃ in a protective atmosphere. Through IDA, Mo/Cu LMMCs are prepared in this paper. The tensile tests carried out for the Mo/Cu LMMCs specimens show that the Mo/Cu interfaces constructed via IDA have high normal and shear strengths. Additionally, the microstructure of the Mo/Cu interface is characterized by High Resolution Transmission Electron Microscopy （HRTEM）, X-ray diffraction （XRD） and Energy Dispersive X-ray （EDX） attached in HRTEM. The microscopic characterization results show that the expectant diffusion between Mo and Cu occurs through the irradiation damage during the process of IDA. Thus a Mo/Cu metallurgical bonding interface successfully forms. Moreover, the microscopic test results show that the Mo/Cu metallurgical interface is mainly constituted of crystalline phases with twisted and tangled lattices, and amorphous phase is not observed. Finally, based on the positron annihilation spectroscopy （PAS） and HRTEM results, the diffusion mechanism of IDA is discussed and determined to be vacancy assisted diffusion.

Reduced He ion irradiation damage in ZrC-based high-entropy ceramics

Excellent irradiation resistance is the basic property of nuclear materials to keep nuclear safety.The high-entropy design has great potential to improve the irradiation resistance of the nuclear materials,which has been proven in alloys.However,whether or not high entropy can also improve the irradiation resistance of ceramics,especially the mechanism therein still needs to be uncovered.In this work,the irradiation and helium(He)behaviors of zirconium carbide(ZrC)-based high-entropy ceramics(HECs),i.e.,(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C,were investigated and compared with those of ZrC under 540 keV He ion irradiation with a dose of 1×10^(17) cm^(−2) at room temperature and subsequent annealing.Both ZrC and(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C maintain lattice integrity after irradiation,while the irradiation-induced lattice expansion is smaller in(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C(0.78%)with highly thermodynamic stability than that in ZrC(0.91%).After annealing at 800℃,ZrC exhibits the residual _(0.2)0%lattice expansion,while(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C shows only 0.10%.Full recovery of the lattice parameter(a)is achieved for both ceramics after annealing at 1500℃.In addition,the high entropy in the meantime brings about the favorable structural evolution phenomena including smaller He bubbles that are evenly distributed without abnormal coarsening or aggregation,segregation,and shorter and sparser dislocation.The excellent irradiation resistance is related to the high-entropy-induced phase stability,sluggish diffusion of defects,and stress dispersion along with the production of vacancies by valence compensation.The present study indicates a high potential of high-entropy carbides in irradiation resistance applications.

Mechanical property and irradiation damage of China Low Activation Martensitic(CLAM) steel

China Low Activation Martensitic （CLAM） steel is being studied to develop the structural materials for a fusion reactor, which has been designed based on the well-known 9Crl.5WVTa steel. The effect of tempering temperature on hardness and micro- structure of CLAM steel was studied. The strength of CLAM steel increased by adding silicon, and the ductility remained con- stant. Conversely, while CLAM steel maintained good ductility with the addition of yttrium, its tensile strengths were greatly degraded. Behaviors under electron irradiation of CLAM steel were examined using the high voltage electron microscope. Electron irradiation at 450℃ formed many voids in CLAM steel with basic composition, whereas CLAM with silicon steel did not change the microstructure significantly.