Evolution Of Helium Bubbles Research Articles

Helium bubble evolution in Zr alloys: Effects of sinks and temperature

Implanted helium resulting from fusion reactions can pose a significant threat to zirconium alloys used as fusion reactor materials. Intrinsic structures and temperatures in nuclear materials can significantly influence the behavior and distribution of these helium bubbles under irradiation. Therefore, the behavior of helium bubbles in zirconium alloys was investigated by in-situ He+ irradiation at 573 K, 623 K, 673 K, 723 K and 773 K. Results indicated that the smallest and densest bubbles are found at GBs, while the largest helium bubbles are observed near precipitates. The size of the helium bubbles first increased and then decreased with an increase in temperature, while the density of bubbles changed in the opposite trend. The swelling induced by irradiation was maximum at 673 K when the irradiation dose was constant, while at this temperature, the geometry of the helium bubble changed from spherical to polygonal with a larger size than those at other temperatures.

Investigating the temperature dependence of helium bubble dynamics in plasma exposed tungsten via in-situ TEM annealing

In-situ TEM annealing and imaging were performed on tungsten samples pre-exposed at either 573 K or 1013 K in a pure helium plasma to a fluence of 1025 m−2. To investigate the thermal evolution of helium bubbles, the samples were imaged for annealing temperatures up to 998 K in steps of 100 K. It is found that annealing temperatures had little effect on the bubble dynamics for the lower temperature exposure of 573 K. Elongated bubble structures remained in the sample throughout the annealing process and there is minimal change in both the average bubble size and cross-sectional number density. However, annealing had a significant effect on the higher temperature exposure of 1013 K. Bubbles were found to be trapped in large clusters and increasing annealing temperature caused a significant increase in the average bubble size accompanied by a decrease in the cross-sectional bubble number density. The experimental observations are supported by theoretical calculations that show a simultaneous increase in the average number of He atoms per bubble in the higher exposure temperature sample but an overall decrease in He atoms retained within bubbles as the annealing temperature increased. These trends in bubble dynamics with annealing temperature suggest that Ostwald ripening dominates, whereby bubble growth is determined by the different pressures of different bubble sizes, rather than through bubble migration and coalescence.

Superior radiation resistance of ODS-RAFM steels revealed by Positron annihilation spectroscopy study

Oxide-dispersion-strengthened (ODS) reduced-activation ferritic/martensitic (RAFM) steels are considered as most promising structural materials for fusion reactors and other advanced nuclear systems due to its excellent irradiation resistance under high dose irradiations. However, the extreme complex synergistic effect between transmuted helium/hydrogen and displacement damage which most seriously affects the structure and mechanical properties of ODS-RAFM steels is very difficult to understand, especially the role of hydrogen still remains unclear. Taking advantage of very sensitive to small vacancy clusters of Positron annihilation spectroscopy (PAS) method, we conducted irradiation defect study on ODS-RAFM, RAFM and its corresponding model alloy Fe–9Cr and α-Fe to investigate their anti-swelling properties at the early stage of irradiation with hydrogen-helium synergism and the mechanism. Three distinct irradiation schemes including (1) single Fe ion beam, (2) simultaneous Fe and He (named Fe + He) ion beam, (3) subsequent H ion injection after Fe + He (named Fe + He/H) ion beam irradiation were performed. Hydrogen-helium synergistic effects on vacancy evolution within these steels were explored combining the first-principles calculation. The implantation of He was observed to significantly increase defect concentration among all four steels, while H exhibited interestingly complexity on affecting the evolution of helium bubbles. The H post-injection increased defect concentration obviously in the materials with abundant sinks, but improved poorly in ones with rare sinks. Through the systematic study of the interactions between H, He, and vacancies, it was revealed that even at the early irradiation stage, ODS-RAFM steels has already exhibited excellent irradiation resistance compared to other alloys across three irradiation schemes.

Evolution of helium bubbles in FeCoNiCr-based high-entropy alloys containing γ′ nanoprecipitates

Abstract A series of high-entropy alloys (HEAs) containing nanoprecipitates of varying sizes is successfully prepared by a non-consuming vacuum arc melting method. In order to study the irradiation evolution of helium bubbles in the FeCoNiCr-based HEAs with γ′ precipitates, these samples are irradiated by 100-keV helium ions with a fluence of 5×1020 ions/m2 at 293 K and 673 K, respectively. And the samples irradiated at room temperature are annealed at different temperatures to examine the diffusion behavior of helium bubbles. Transmission electron microscope (TEM) is employed to characterize the structural morphology of precipitated nanoparticles and the evolution of helium bubbles. Experimental results reveal that nanosized, spherical, dispersed, coherent, and ordered L12-type Ni3Ti γ′ precipitations are introduced into FeCoNiCr(Ni3Ti)0.1 HEAs by means of ageing treatments at temperatures between 1073 K and 1123 K. Under the ageing treatment conditions adopted in this work, γ′ nanoparticles are precipitated in FeCoNiCr(Ni3Ti)0.1 HEAs, with average diameters of 15.80 nm, 37.09 nm, and 62.50 nm, respectively. The average sizes of helium bubbles observed in samples after 673-K irradiation are 1.46 nm, 1.65 nm, and 1.58 nm, respectively. The improvement in the irradiation resistance of FeCoNiCr(Ni3Ti)0.1 HEAs is evidenced by the diminution in bubbles size. Furthermore, the FeCoNiCr(Ni3Ti)0.1 HEAs containing γ′ precipitates of 15.8 nm exhibits the minimum size and density of helium bubbles, which can be ascribed to the considerable helium trapping effects of heterogeneous coherent phase boundaries. Subsequently, annealing experiments conducted after 293-K irradiation indicate that HEAs containing precipitated phases exhibits smaller apparent activation energy (E a) for helium bubbles, resulting in larger helium bubble size. This study provides guidance for improving the irradiation resistance of L12-strengthened high-entropy alloy.

The synergetic effect of He and Kr irradiation on helium bubble evolution in SiC/SiC composite: Combining in-situ TEM observation with MD simulation

SiC fiber reinforced SiC matrix composites (SiC/SiC composites) are considered as one of the promising structural materials for liquid type breeding blanket in the fusion energy system. The transmutation gas production rate in fusion reactor is significantly higher compared with fission reactors. An innovative method combining in-situ irradiation and TEM observation and MD simulation was utilized to evaluate the synergetic effects of helium and irradiation on SiC/SiC composites. A comprehensive experiment matrix including Kr irradiation, He pre-implantation with sequential Kr irradiation as well as simultaneous dual beam at 1073 K to 16 dpa and 2400 appm He (150 appm/dpa) was performed using 800 keV Kr and 50 keV He ions. With the support of MD results, the impact of relative concentration ratio of vacancies and helium atoms on the bubble evolution was systematically investigated and the corresponding mechanism was further unraveled, which provides the basis of limiting the bubble density in SiC/SiC composites. Additionally, the direct evidence for the competition of irradiation-assisted bubble growth and re-dissolution was in-situ observed in SiC matrix for the first time.

The behavior of helium bubble evolution under neutron irradiation in different tungsten surfaces

Tungsten, as a kind of material for the plasma-facing wall in fusion reactor and tokamak, is subjected to irradiation by the high-energy neutron and the high fluxes of hydrogen and helium plasmas. Especially, in the presence of helium (He) bubbles, neutron irradiation can significantly exacerbate the deterioration of the material's mechanical properties. However, due to experimental limitations, the evolution of He bubbles in tungsten irradiated by neutrons and the underlying mechanisms remain unclear. Here, molecular dynamics (MD) simulation is used to investigate the behavior of He bubbles in tungsten with different crystal surfaces irradiated by neutrons. We observed the complete evolutionary process of the He bubble, i.e. standing, expanding, and bursting. During this process, high-energy neutron transfers energy to atoms within the He bubble through cascade collision, leading to a rapid increase in energy and pressure of the He bubble, and then the rapid expansion of the He bubble makes the pressure rapidly released, ultimately leading to the rupture of the helium bubble. Furthermore, we also explore the evolution of the He bubble under varying conditions (such as temperature, neutron energy, and He/vacancy ratio) within the same crystal surface. We found that at lower temperatures and neutron energy with a higher He/vacancy ratio, it tends to form pinhole-like channels to release helium atoms, resulting in the He bubble bursting. On the contrary, it tends to form a hill-like expansion to spurt helium atoms out, leading to the bubble bursting. Additionally, it was found that the direction and time of He bubble rupture varied under different crystal surfaces. He bubbles under the (112) surface burst the slowest with excellent corrosion resistance. These findings provide new insights into the behavior of irradiation resistance of fusion reactor materials under extreme conditions and offer significant guidance for the improvement and selection of optimal materials for plasma-facing walls.

Helium bubble evolution under cascade in bcc iron relevant to fusion conditions investigated by a novel coupling MD-OKMC method

The direct interaction between cascade and helium bubbles during the thermal spike phase plays an important role in the helium bubbles evolution in metals, which was not fully considered by the present long-time simulation methods. To address this issue, in this work we developed a coupling MD-OKMC method to investigate the helium bubble evolution under irradiation cascade in bcc iron. The short-time collision cascade was simulated by the molecular dynamics (MD), and the long-time helium bubble evolution was modeled by the object kinetic Monte Carlo (OKMC). The MD and OKMC simulations were alternated to imitate the gradual increase of both irradiation dose and helium concentration under experiment conditions. The impact of temperature on the helium bubble evolution under irradiation cascade in bcc iron was investigated and the results were compared with the data from neutron irradiation experiment. It's found that the results of the coupling MD-OKMC were consistent with the experiment results, and were better in agreement with the experiment than the traditional OKMC.

TEM investigation of helium bubble evolution in tungsten and ZrC-strengthened tungsten at 800 and 1000°C under 40keV He+ irradiation

Helium-induced defect nucleation and accumulation in polycrystalline W and W0.5 wt%ZrC (W0.5ZrC) were studied in-situ using the transmission electron microscopy (TEM) combined with 40 keV He+ irradiation at 800 and 1000°С at the maximum damage level of 1 dpa. Radiation-induced dislocation loops were not observed in the current study. W0.5ZrC was found to be less susceptible to irradiation damage in terms of helium bubble formation and growth, especially at lower temperature (800 °C) when vacancies were less mobile. The ZrC particles present in the W matrix pin the forming helium bubbles via interaction between C atom and neighbouring W atom at vacancies. This reduces the capability of helium to trap a vacancy which is required to form the bubble core and, as a consequence, delays, the bubble nucleation.At 1000 °C, significant bubble growth occurred in both materials and all the present bubbles transitioned from spherical to faceted shape, whereas at 800 °C, the faceted helium bubble population was dominated in W.

Shrinkage and coalescence behavior of helium bubbles in Fe9Cr1.5W0.4Si F/M steel under the coupling effect of compression stress and temperature

As important irradiation defects, helium bubbles will threaten the stability and reliability of reactor structural materials. Extensive research has been conducted on the dynamic response of helium bubbles under thermal annealing, irradiation, or tension, but the behavior and mechanisms of helium bubble evolution under compression remain to be understood. Here, by adopting in-situ cyclic nanocompression testing on Fe9Cr1.5W0.4Si F/M steel containing helium bubbles at 673 K, we present direct experimental evidence for the shrinkage and coalescence behavior of helium bubbles under the coupling effect of compression stress and temperature for the first time. Unlike the stress-free condition where the bubble size shows an increasing trend, compressive stress causes the bubble to shrink. Moreover, the large-sized bubbles show a greater change in size than small-sized bubbles. At 673 K, there is no thermal motion of the bubbles in F/M steel, and it is the deformation and mutual squeezing of bubbles under compression that causes the coalescence of tightly arranged bubbles. Furthermore, helium bubbles can act as dislocation sources to emit dislocations under compression, and the emitted dislocations can in turn envelope around the helium bubbles, thus hindering bubble coalescence and leading to the formation of deformed bubbles.

A comprehensive atomistic investigation on the cascade induced helium bubble motion in bcc iron for neutron irradiated RAFM steels

Cascade induced by the primary knock-on atom could significantly influence the evolution of helium bubbles in RAFM steels. In this work, the helium bubble migration and helium bubbles coalescence under cascade overlapping, i.e., when the helium bubble was overlapped by the thermal spike of one cascade, in bcc Fe was investigated by molecular dynamics simulation. The influence of He-to-vacancy (He/V) ratio as well as cascade energy, temperature, bubble size and bubbles distance were investigated based on the statistical results of 4700 cases. A method which could quantitatively estimate the overlapping extent between the cascade and helium bubbles was put forward to confirm that the cascade did overlap with the helium bubble in all cases. It was found that under cascade overlapping, the helium bubble tends to migrate toward the thermal-vacancy-rich center. The mechanisms of migration change from vacancy diffusion to He atoms migration with the increase of the He/V ratio, and the corresponding migration distance could decrease one order of magnitude. The cascade induced coalescence of two close helium bubbles is associated with the synergy effect of migration, dissociation and joint strain field of the two bubbles. Especially, it was found that the joint strain field of two close helium bubbles could significantly promote the bubbles’ coalescence by fostering the two bubbles’ directional migration towards each other under cascade overlapping. It was also found that the stable He/V ratio of helium bubble under cascade overlapping is around 0.5.

Evolution of helium bubbles induced by helium irradiation in polycrystalline palladium: An insight into tritium aging

Essential insight into evolution principles of helium (He) bubbles within Palladium (Pd), a prominent hydrogen isotope storage and tritium handling material, is of great importance to understand the service performance of such transition metal in the field of nuclear industry. Particularly, the features of He bubbles and their evolution details have long been attracting broad interests. Herein, He bubbles with different structural features and corresponding distinct evolving processes within polycrystalline Pd were investigated by transmission electron microscopy (TEM), elastic recoil detection (ERD) and thermal desorption spectroscopy (TDS). He bubbles were induced and regulated by irradiation conditions. Comprehensive characterizing results indicate that bubbles with small sizes, spherical shape and uniform distribution, realized by low-fluence irradiation, are inclined to be stable in Pd matrix, while coarsened bubbles with faceted shape and regional distribution in the high-fluence condition are prone to release at relatively low temperatures. Meanwhile the evolving processes of He bubbles including migration, coarsening and releasing within polycrystalline Pd were analyzed. The impact of the structural characteristics such as surfaces or grain boundaries of Pd, acted as “fast path” for bubble diffusion, coarsening and release, was systematically discussed. Moreover, the correlation between tuned irradiation and actual tritium aging was discussed by analyzing He concentrations and bubble sizes in both processes. The study reveals important features of He bubble evolution in Pd, which will provide positive reference for understanding correlative behaviors in other irradiation conditions, especially tritium aging. • He bubbles with different features were obtained by tuning fluence and energy of He + irradiation. • Evolution behaviors of He bubbles including nucleation, migration and coarsening were studied by TEM, ERD and TDS. • The stability of He bubble is closely related to the size that small one inclines to stabilize while large one tends to release. • Trapping and coarsening of He bubbles are promoted in grain boundaries and structural defects. • Different evolution periods of He bubble in this study were analyzed for the purpose to offering an analogous reference for tritium aging.

Modeling tungsten response under helium plasma irradiation: a review

Tungsten, a leading candidate for plasma-facing materials (PFM) in future fusion devices, will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions. In the past two decades, experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering, thermal and other properties of tungsten, posing a serious danger to the performance and lifetime of tungsten and the steady-state operation of plasma. In this article, we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles, surface morphology, and property changes of tungsten exposed to low-energy helium plasma. The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.

Effect of periodic thickness on the helium bubble evolution and irradiation hardening in Cu/W(Re) multi-layered films under helium ion irradiation

Based on the basic understanding of prominent helium (He) bubble storage and defect annihilation in the dual-phase heterogeneous interfaces designed in nano-meter materials, the Cu/W(5.31 at.% Re) multilayered films with nominal periodic thickness (h) ranging from 2 nm to 50 nm were irradiated by 60 keV He+ at irradiation temperature of 725 K. At the fluence of 2×1017 cm-2, the lamellated interfaces in the Cu/W(Re) multilayered film of h = 2 nm were broken down due to the irradiation-induced intermixing between the Cu-W(Re) neighbouring interfaces, resulting in a stable distribution of bubble in grains or at grain boundaries. However, at He concentration peak region, the bubble clusters inside the Cu layers and the blurred interfaces were formed in the Cu/W(Re) multilayered film of h = 10 nm. The W phase structure was changed by the aggregated bubbles in lattices, and the Cu layers were damaged due to the distribution scope of aggregated bubble-cluster approximately increased to a critical periodic thickness (10 nm). The lamellated interfaces still kept stable at low He concentration region. The calculated bubble pressure and He density inside bubbles can effectively explain the lattice distortion induced partial phase transformation from α-W to γ-W in the W(Re) layers. Moreover, the effects of interfaces, He bubbles and dislocations on the increase of nano-hardness in the irradiated multilayers were discussed in detail.

A combined rate theory-population balance model of the evolution of irradiation-induced helium bubbles in metals during annealing

A multiscale model describing the evolution of helium bubbles in the irradiated materials is established based on the rate equations and the population balance equation. The size distribution of the helium bubbles and the evolution law of the statistical average size and number density of the bubbles with time changing predicted by the model are in good agreement with the experimental statistics. The influence of annealing temperature, annealing time, irradiation energy, irradiation flux, and coarsening mechanisms on the evolution of helium bubbles are numerically simulated and discussed, taking FeCrAl alloy as the irradiated material. The results show that the bubble evolution is dominated by the Ostwald ripening mechanism under high temperature annealing conditions (≥ 1073 K), and the time dependence of the average size and density of helium bubbles is consistent with the existing theoretical results. And the number of shrinking helium bubbles caused by Ostwald ripening is effectively reduced by the bubble coalescence effect, leading to further growth of the proportion of large-sized helium bubbles. Consequently, a Gaussian bubble size distribution has been obtained modeling the coupling of the Ostwald ripening mechanism and the bubble coalescence mechanism. The generation rates of helium and vacancy in the material during irradiation, as well as their ratio, are significant factors that can affect the nucleation and evolution of helium bubbles.

On the helium bubble swelling in nano-oxide dispersion-strengthened steels

The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes. In radiation environments with high transmutation helium production rates such as in fusion and spallation applications, even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation. While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level, these, however, do not overlap with the size resolution of available experimental techniques. In this study, we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids. In combination with transmission electron microscopy, we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM. Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution, where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.

Evolution of helium bubbles in SLM 316L stainless steel irradiated with helium ions at different temperatures

The temperature dependence of helium bubble evolution in 316L stainless steel (SS) fabricated by selective laser melting (SLM) has been studied by performing 500 keV helium ion irradiation at temperatures between 350 and 900 °C. The number density of helium bubbles decreased steadily whereas the bubble diameter gradually increased with increasing temperature. The material swelling caused by helium bubbles had no obvious change at the temperature below 800 °C. However, at the maximum temperature of 900 °C, the swelling sharply increased to 0.17% mainly due to the rapidly growing bubble diameter. In particular, heterogeneous nucleation of bubbles occurred in the vicinity of dislocation structures at high temperatures of 700–900 °C, and the formed helium bubbles rapidly grew at the oxide-matrix interface at 900 °C. It was confirmed various intrinsic structures (dislocation structures or oxide particles) differently affected the bubble evolution process. The apparent activation energy (Eact) of helium bubbles determined by the Arrhenius model were used to elucidate the most probable helium bubble evolution mechanisms at various temperatures, as it is an experimentally observed activation energy, which contained information about the activity of helium atoms. It was found that the low-temperature regime with low apparent activation energies (ECbact=0.15eV,ERbact=0.04eV) and high-temperature regime with high apparent activation energies (ECbact=1.50eV,ERbact=0.58eV) favored different helium bubble evolution mechanisms. In the low-temperature regime, helium bubble evolution was controlled by the diffusion of helium atoms via a vacancy mechanism in the SLM 316L SS. On the other hand, the migration and coalescence of helium bubbles also occurred in the high-temperature regime which caused the apparent activation energy of density was higher than the theoretical value of helium atoms diffuse via a replacement mechanism.

Evolution mechanisms of irradiation-induced helium bubbles, C15 clusters and dislocation loops in ferrite/martensite steels: A cluster dynamics modeling study

• Evolution of helium bubbles , C15 clusters and dislocation loops is studied by a cluster dynamics model. • The model considers the formation of C15 clusters and followed transformation into loops. • Irradiation temperature and dose effects on the microstructural evolution are analyzed. • Helium bubble evolution upon irradiation is governed in sequence by three phases. • Loop growth driven by long-term defect migration follows a power law. Using a cluster dynamics model, we studied the evolution of helium bubbles, C15 clusters and dislocation loops produced by Fe 3+ /He + dual ion beam irradiation in reduced activation ferrite/martensite Eurofer97 steels. The model reasonably reproduced size distributions of experimentally detected helium bubbles and dislocation loops. We show that bubble evolution upon irradiation was governed by three phases in sequence: bubble nucleation dominated phase controlled by irradiation cascade, coupled phase of bubble nucleation and growth, and bubble growth dominated phase. As a first attempt, the model considers the formation of widely reported C15 clusters and develops a scheme for C15 clusters transformation into loops. We show that the loop growth driven by long-term defect migration follows a power law f(n) ~ a/n S . The increase of irradiation temperature from 603 K to 673 K promoted the growth of C15 clusters resulting in pronounced loop evolution. While at 773 K, the high flux of vacancies and low fluxes of single, di- and tri-interstitials suppressed loop nucleation and growth, leading to no loop formation confirmed by experiment. The effectiveness of the model developed in this study demonstrates its potential to be used in similar irradiation cases.

Helium bubble formation and evolution in NiMo-Y2O3 alloy under He ion irradiation

We report helium ion irradiation experiments for a new type of dispersion-strengthened NiMo-Y2O3 alloy with three different irradiation doses and varying irradiation dose rates at 750 °C to evaluate its helium-induced damage behavior. Transmission electron microscopy was used to reveal the evolution of helium bubbles after irradiation. The experimental results show that with increasing ion dose, the number density of helium bubbles increases continuously. However, the mean size of helium bubbles first increases and then decreases, mainly due to the varied ion dose rates. The volume fractions of helium bubbles in the three investigated samples after irradiation are 0.15%, 0.32%, and 0.27%, which are lower than that of the Hastelloy N alloy (0.58%) after similar irradiation conditions. This indicates that the NiMo-Y2O3 alloy exhibits better helium-induced-swelling resistance than the Hastelloy N alloy, highlighting its potential applicability to MSRs, from the perspective of irradiation performance.

In-situ TEM observation of microstructure evolution in Fe9Cr1.5W0.4Si alloy during He+ irradiation and post-implantation annealing

The evolution of helium bubbles in a newly developed Fe9Cr1.5W0.4Si alloy that is an important candidate used as fuel claddings in the Lead-cooled fast reactors was in-situ investigated by transmission electron microscopy during 30 keV He+ irradiation at 500 °C and subsequently annealed at 600 °C. Meanwhile, the evolution of dislocation loops was in-situ researched in the initial stage of irradiation. Two mechanisms including the absorption of irradiation defects and the combination of dislocation loops induced the loop growth. Both He+ irradiation and subsequently annealing induced the initiation, migration, aggregation, and growth of helium bubbles, and changed their shape from spherical to preferential faceted. But it was more obvious under the annealing condition. Helium bubbles would preferentially nucleate and grow at dislocation lines and grain boundaries and had large size. The bubble lines formed at dislocation line during helium irradiation, and annealing made them more obvious and larger. A denuded zone with few helium bubbles appeared near grain boundary, but its width decreased with the increase of helium fluence and annealing time. Meanwhile, annealing would lead to the appearance of super large helium bubbles at grain boundaries. The irradiation hardening and swelling were increased with the increase of helium fluence. The corresponding mechanism was analyzed based on in-situ experimental observation.

Temperature dependence of He bubble evolution in UNS N10003 alloys under He ion irradiation

The effects of irradiation temperature on helium bubble evolution in UNS N10003 alloys were studied using 500 keV He ion irradiation at a dose of 2 × 1016 ions/cm2 from 650 to 850 °C. As the irradiation temperature increased, the density of the helium bubbles decreased and their size increased. Polyhedral bubbles were observed at 850 °C, and the non-spherical shapes of these bubbles reduced their surface energy. The densities and mean diameters of the bubbles at 650–850 °C show Arrhenius behaviors with activation energies of 1.06 ± 0.17 and 0.35 ± 0.02 eV, respectively. The activation energies indicate that the He bubble evolution at temperatures ranging from 650 to 850 °C is not only controlled by He diffusion via a self-interstitial/He replacement mechanism but is also affected by the migration and coalescence of He clusters or bubbles via surface diffusion. Furthermore, bubble-loop complexes were observed at 750 and 850 °C. With the temperature increasing, the helium bubbles prompted the growth of dislocation loops, suggesting that the interaction between the helium bubbles and the dislocation loops is dependent on the irradiation temperature.