MeV 58Ni Research Articles

Microstructural evolution in doped high entropy alloys NiCoFeCr-3X (X=Pd/Al/Cu) under irradiation

Commonly studied equatomic single-phase FCC high entropy alloys based on 3d transition metals like NiCoFeCr do not provide adequate strength and radiation resistance at high doses for nuclear structural applications. In the current study, the major alloying effects like lattice distortion, ordering and clustering tendencies were investigated by adding low concentration of Pd, Al, or Cu respectively to study the doping effects on the ion irradiation response of NiCoFeCr alloy. The alloys were irradiated with 3 MeV Ni2+ ions at 500 °C to a fluence of 1 × 1017/cm2 at a beam flux of approximately 2.8 × 1012 ions/cm2/s. The microstructural evolution upon irradiation i.e., formation of dislocation networks, radiation induced segregation and precipitation, and void formation were studied in detail. Post-irradiation characterization results showed that a Pd addition leads to a high void nucleation rate but controlled void growth, which may be attributed to increased lattice distortion. In Al added HEA, our microstructural analysis indicates that radiation induced ordered L12 precipitates do not affect void swelling significantly. Cu addition led to Cu precipitation that drastically suppressed dislocation density and void swelling of the alloy. Additionally, a model was developed to qualitatively describe the trend in void swelling of typical FCC alloys under ion irradiation. This model was able to qualitatively explain the suppression and reappearance of void swelling in ion irradiated alloys that generally occurs near the region with peak implanted ion concentration.

Decay spectroscopy at the two-proton drip line: Radioactivity of the new nuclides 160Os and 156W

The radioactivity of 76160Os84 and 74156W82 that lie at the two-proton drip line has been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The 160Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV 58Ni ions bombarding a 106Cd target. The 160Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of 160Os (Eα = 7092(15) keV, t1/2 = 97−32+97 μs) and its isomeric state (Eα = 8890(10) keV, t1/2 = 41−9+15 μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate the β decays of the ground state of 156W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, 156Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in 73156Ta83 of 333−22+25 ms was obtained in a separate experiment using the same experimental systems with a 102Pd target. This result was employed to improve the precision of the half-life determined for 156W, which was measured as 157−34+57 ms.

Radiation-induced hardening of ion-irradiated Zircaloy-2 at 573 K under applied stress

The microstructural evolution and hardening of Zircaloy-2 under low-dose irradiation (<1.0 dpa) with 3.2 MeV Ni3+ ions under applied stress at 573 K were investigated using transmission electron microscopy (TEM) examination and nano-indentation measurements in this study. The irradiation doses ranged from 0.05 to 1 dpa. The formation of < a > loops was observed at doses below 0.05 dpa, and the density was found to be saturated at about 0.1 dpa. The < a > loops then grew and intersected with adjacent loops to become entangled at doses above 0.4 dpa. Radiation-induced hardening was confirmed in Zircaloy-2 at the early stage of irradiation below 0.1 dpa, and the hardening effect was attributed to the nucleation and growth of < a > loops. The Orowan equation was used to estimate the contribution of dislocation loops to the hardening, and the estimated values were in good agreement with the experimental results, with the obstacle strength factor of < a > loops as 0.25. Furthermore, the effect of applied stress of 1 dpa irradiated tensile samples on radiation-induced hardening was also discussed. This study provides dislocation loop formation and hardening behavior of Zircaloy-2 under low-dose irradiation at 573 K with stress conditions.

The Fe addition as an effective treatment for improving the radiation resistance of fcc NixFe1-x single-crystal alloys

In this work, five different compositions of fcc Ni and NixFe1-x single crystal alloys namely Ni, Ni0.88Fe0.12, Ni0.77Fe0.23, Ni0.62Fe0.38, Ni0.38Fe0.62 were irradiated by 1.5 MeV 58Ni ions at room temperature in a wide fluence range (4 × 1013 to 4 × 1015 ions/cm2). The role of Fe addition on the radiation resistance of the NixFe1-x single crystals was studied by transmission electron microscopy (TEM), ion channeling technique (RBS/C) and nanoindentation techniques. The Multi-Step Damage Accumulation analysis revealed the cross-sections for damage formation significantly decreases for Ni0.38Fe0.62 and Ni0.62Fe0.38 as compared to that in pure Ni single crystal, which is consistent with RBS/C and TEM results. The results of nanoindentation show that Ni0.62Fe0.38 alloy possesses the highest hardness (2.96 GPa) among the other compositions in a pristine state. To interpret this result, hybrid Monte Carlo/ Molecular dynamics simulations were used to check the presence of the ordered crystal phase structure for NixFe1-x binary alloys. The simulation results have shown that depending on the iron content, we deal with different amounts of FeNi3 (L12) phase. This result revealed that in Ni0.62Fe0.38 alloy, nanoprecipitate FeNi3 (L12) phase (around 20%) is formed inside the disordered matrix, which could be one of the main reasons for the high hardness of this alloy before irradiation.Additionally, we have found adding iron reduced the number and size of the defects (as a result of ion irradiation) in NixFe1-x because the Fe element is more stable than Ni, which results from the electron configuration of both elements in the excited state. Therefore, the more iron in the material, the fewer defects are created.

Taming the Pseudoelastic Response of Nitinol Using Ion Implantation

Implantation of Ni50.5Ti49.5 wire with 30 MeV Ni6+ ions at doses (< 0.1 DPA) typically smaller than employed in the literature is shown to systematically alter the pseudoelastic response, with extrema in Berkovich nanoindentation load (+50%), hysteresis (−60%), and recoverable displacement (−19%) occurring at ∼ 3.6 μm below the implantation surface. These extraordinary values are attributed to ∼ 10 to 20 nm amorphous clusters that constrain the stress-induced B2-B19′ phase transformation. This is substantiated by phase field simulations of crystalline-amorphous composites and molecular dynamics simulations of crystalline-vacancy cluster composites showing the spatial refinement of martensite caused by nm-scale defects. The results suggest that ion implantation may potentially expand the processing and performance space for NiTi, by creating amorphous defects at smaller length scales than dislocation substructures produced by conventional deformation processing.

Phase stability, mechanical properties, and ion irradiation effects in face-centered cubic CrFeMnNi compositionally complex solid-solution alloys at high temperatures

Two CrFeMnNi face-centered cubic complex concentrated solid-solution alloys (CSA) have been evaluated for phase stability, mechanical properties, and radiation damage effects from heavy ions. Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35 were predicted by thermodynamic calculations to phase separate and maintain a single phase at 700 °C, respectively. Aging experiments at this temperature confirmed varying degrees of precipitation of a body-centered cubic phase in both Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35. The alloys showed promising strength in tensile deformation at room temperature, with yield strengths of 155 MPa and 151 MPa for Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35, respectively. At 500 °C, the yield strength of Cr18Fe27Mn27Ni28 fell to 93 MPa, and to 100 MPa in Cr15Fe35Mn15Ni35. Unlike Cr18Fe27Mn27Ni28, Cr15Fe35Mn15Ni35 gained some ductility at 500 °C compared to room temperature. The two CSAs were irradiated to 75 dpa at 500 °C in the plateau region of the displacement curve using 3.7 MeV Ni2+ ions, alongside model alloy 709 as a reference. Irradiation results produced similar densities and sizes of dislocations loops in the two CSAs compared to the reference. However, while large voids form in the plateau region of Cr18Fe27Mn27Ni28, small voids form just beyond the displacement peak of Cr15Fe35Mn15Ni35. Atom probe tomography and energy dispersive X-ray spectroscopy-equipped scanning transmission electron microscopes were used to characterize the alloys for changes in chemical distribution.

Swelling resistance of an austenitic stainless steel with uniformly distributed nanosized NbC precipitates under heavy ion irradiation

The void swelling behavior of a newly developed austenitic stainless steel with uniformly distributed nanosized NbC precipitates (ARES-6) and commercial 316 stainless steel was evaluated using the heavy ion irradiation. The 5 MeV Ni3+ ion was irradiated at 500 °C to a dose of 8.5 dpa with a dose rate of 1.8 × 10−3 dpa/s at 600 nm from the surface. Measured at 600 nm region, ARES-6 showed nearly seven times less swelling compared to that of 316 stainless steel. By comparing the swelling for the solution annealed and hot-rolled ARES-6, it was confirmed that NbC precipitates as well as high Ni content contributed to the improved swelling resistance of the alloy. The dissolution of nanosized NbC precipitates during irradiation was observed, which could be the reason for the large discrepancy between estimated and observed swelling resistance of ARES-6.

Work Function Modulation of Few-Layer Graphene by Swift Heavy Ion Irradiation.

Here, we report the structural and electronic modification induced in chemical vapor deposited graphene by using swift heavy ions (70 MeV Ni6+).Raman spectroscopy was used to quantify the irradiation-induced modification in vibrational properties. The increase in defect density with fluence causes an increase in the intensity ratio of its characteristic Raman D and G band. The increase in defect density also results in a decrease in crystallite size. The changes in the crystal structure are observed from X-rays diffraction measurement. Swift heavy ion irradiation induced defect, modified the surface roughness and surface potential of graphene thin film as measured from atomic force microscopy and scanning Kelvin probe microscopy respectively. The increase in the work function, surface roughness as well as defect concentration with fluence, indicate the possibility of linear correlation between them. Presence of defects in graphene sheets strongly affects surface electronic and optical properties of the material that can be used to tailor the optoelectronics device performance.

Anisotropic nanostructure formation by vapor etching of ion tracks in α-quartz

In this study, latent and etched ion tracks generated by high electronic excitation in alpha quartz (α-SiO2) were characterized. Single crystals of Y- and Z-cut α-SiO2 were irradiated at room temperature with 20 MeV Ni6+ ions and 40 MeV I7+ ions. The track morphology depends on the energy of the incident ion and the stopping power on the target material. Subsequent chemical vapor-etching with hydrofluoric acid solutions was conducted with varying etching times and acid concentrations. The vapor etching process produced nanostructures whose dimensions increased with etching time and etchant concentrations. Y-cut samples etched more slowly than Z-cut samples and exhibited anisotropic track etching behavior. Production of nanowells with different aspect ratios was accomplished by altering the etching time and etchant concentration. The nanowells were characterized by Atomic Force Microscopy. The etched nanostructure templates could be used in the fabrication of novel nanodevices with unique optical, thermal, and electronic properties.

Desorption of Implanted Deuterium in Heavy Ion-Irradiated Zry-2

To understand the degradation behavior of light water reactor (LWR) fuel-cladding tubes under neutron irradiation, a detailed mechanism of hydrogen pickup related to the point defect formation (i.e., a-component and c-component dislocation loops) and to the dissolution of precipitates must be elucidated. In this study, 3.2 MeV Ni3+ ion irradiation was conducted on Zircaloy-2 samples at room temperature. Thermal desorption spectroscopy is used to evaluate the deuterium desorption with and without Ni3+ ion irradiation. A conventional transmission electron microscope and a spherical aberration-corrected high-resolution analytical electron microscope are used to observe the microstructure. The experimental results indicate that radiation-induced dislocation loops and hydrides form in Zircaloy-2 and act as major trapping sites at lower (400–600 °C) and higher (700–900 °C)-temperature regions, respectively. These results show that the detailed microstructural changes related to the hydrogen pickup at the defect sinks formed by irradiation are necessary for the degradation of LWR fuel-cladding tubes during operation.

Free surface impact on radiation damage in pure nickel by in-situ self-ion irradiation: can it be avoided?

A major issue of in-situ radiation damage studies is related to the influence of free surfaces. Free surfaces in thin foils are indeed strong sinks for radiation-induced defects. Nevertheless, in-situ irradiation is a powerful tool to study real-time microstructural evolution and obtain insight into dynamic mechanisms of radiation damage. Thus, a detailed evaluation of surface effects is essential to validate existing results and provide guideline for future comparative experiments. In this work, nickel is chosen as model material to conduct systematic studies on surface effects due to the high mobility of its self-interstitials. Ultra-high purity Ni thin foils are in-situ irradiated by 2 MeV Ni2+ ions at high temperatures (400-700°C). Microstructural evolution analysis and detailed characterization of dislocation loops are performed in function of specimen thickness.The present work shows: (i) a drastic influence of thickness on the microstructural evolution and irradiated microstructure with the existence of a critical thickness depending on temperature; (ii) a good prediction of an adequate irradiation thickness with a vacancy concentration calculation model; (iii) an impact of free surfaces on the fine distribution of loop Burgers vectors; (iv) a first determination of migration energy of vacancies in Ni considering the temperature dependence of the loop-depleted zones; (v) a production bias model showing that a loss of 10% interstitials favors the growth of vacancy loops observed for the first time in Ni at 510°C.

Temperature-Dependent Cavity Swelling in Dual-Ion Irradiated Fe and Fe-Cr Ferritic Alloys

Fe-Cr ferritic-martensitic (FM) steels are promising structural material candidates for fusion and advanced fission reactors due to their attractive mechanical properties and volumetric swelling resistance. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. In this study, simultaneous dual ion irradiations (8 MeV Ni3+ ions and energy-degraded 3.5 MeV He2+ ions) were used to quantify the cavity swelling behavior in ultra-high purity Fe and Fe-Cr alloys (3-14 wt.% Cr), Fe-10 wt.% Cr-780 wt.ppm C, and Eurofer97 FM steel. The irradiations were conducted over a wide temperature range (400-550 °C) with a mid-range dose of ~30 displacements per atom (dpa) and 0.1 appm/dpa He implantation rate. Using state-of-the-art transmission electron microscopy (TEM), we reveal that pure Fe has a ~50 °C lower peak swelling temperature than Fe-Cr alloys, which is attributed to higher vacancy mobility in pure Fe. Chromium solute appears to strongly suppress cavity swelling in Fe-Cr alloys for temperatures below ~470 °C, but seems to have little effect or slightly enhances swelling above ~470 °C. Cavities were observed in all the irradiated samples between 400-550 °C. This indicates that the narrow temperature range of observable cavities reported in prior ion irradiated Fe-Cr ferritic alloy studies is likely an artefact associated with the use of low ion energies (<5 MeV), which leads to pronounced near-surface and implanted ion effects that suppress cavity swelling even at midrange depths (particularly at high temperatures).

Temperature-dependent cavity swelling in dual-ion irradiated Fe and Fe-Cr ferritic alloys

Fe-Cr ferritic-martensitic (FM) steels are promising structural material candidates for fusion and advanced fission reactors due to their attractive mechanical properties and volumetric swelling resistance. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. In this study, simultaneous dual ion irradiations (8 MeV Ni3+ ions and energy-degraded 3.5 MeV He2+ ions) were used to quantify the cavity swelling behavior in ultra-high purity Fe and Fe-Cr alloys (3-14 wt.% Cr), Fe-10 wt.% Cr-780 wt.ppm C, and Eurofer97 FM steel. The irradiations were conducted over a wide temperature range (400-550°C) with a mid-range dose of ~30 displacements per atom (dpa) and 0.1 appm/dpa He implantation rate. Using state-of-the-art transmission electron microscopy (TEM), we reveal that pure Fe has a ~50°C lower peak swelling temperature difference than Fe-Cr alloys, which is attributed to higher vacancy mobility in pure Fe. Chromium solute appears to strongly suppress cavity swelling in Fe-Cr alloys for temperatures below ~470°C, but seems to have little effect or slightly enhances swelling above ~470°C. Cavities were observed in all the irradiated samples between 400-550°C. This indicates that the narrow temperature range of observable cavities reported in prior ion irradiated Fe-Cr ferritic alloy studies is likely an artifact associated with the use of low ion energies (<5 MeV), which leads to pronounced near-surface and implanted ion effects that suppress cavity swelling even at midrange depths (particularly at high temperatures).

Damage relief of ion-irradiated Inconel alloy 718 via annealing

Inconel alloy 718 is a high-strength and corrosion resistant alloy that is commonly used as a beamline vacuum window. The accumulation of irradiation-induced damage substantially decreases the window’s service lifetime, and replacing it engenders significant beamline downtime. With this application in mind, herein we examine whether post-irradiation annealing can alleviate irradiation-induced damage of Inconel alloy 718. Inconel alloy 718 was received in a solution annealed state. We then irradiated samples using two different modalities (1.5 MeV H+ and 5 MeV Ni2+) at three representative temperatures for beamline windows (room temperature, 100 °C, and 200 °C), followed by annealing at temperatures viable for in-situ annealing processes (no anneal, 300 °C, and 500 °C). Using nanoindentation, we determined that irradiation-induced hardening occurs but is largely mitigated by post-irradiation annealing. Overall, our results suggest that in-situ annealing of radiation damage in Inconel alloy 718 vacuum windows appears feasible, which could potentially decrease beam downtime and maintenance costs.

Effects of irradiation spectrum on the microstructural and mechanical properties of bulk metallic glasses

Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) and Cu60Zr20Hf10Ti10 bulk metallic glass (BMG) specimens were ion irradiated to characterize and compare their irradiation induced microstructural and mechanical property evolution. For the ion irradiations, samples of each BMG were exposed to 9 MeV Ni3+ and 5.5 MeV C+ ions to a midrange (∼1.5 μm depth) dose of 0.5 displacements per atom (dpa) at temperatures ranging from room temperature to 360 °C in order to examine potential effects associated with low (5.5 MeV C) and high (9 MeV Ni) average primary knock on energies. BAM-11 BMG samples were also irradiated by neutrons (E > 0.1 MeV) at ∼70 °C to a fluence of 1.4 × 1020 n/cm2 (dose of 0.1 dpa). Importantly, no pronounced irradiation spectrum effects were observed for the nanoindentation mechanical properties of the two BMGs following ion irradiation. However, significant softening was observed in the BAM-11 BMG sample irradiated by neutrons, while annealing of the unirradiated samples led to a marked increase in hardening. Results of the nanoindentation experiments indicate that softening is caused by irradiation induced creation of free volume defects, while the hardening is caused by their annihilation.

Emerging nuclear collectivity in 124−130Te

The emergence of nuclear collectivity near doubly-magic 132Sn was explored along the stable, eveneven 124−130Te isotopes. Preliminary measurements of the B(E2; 41+ → 21+) transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the g factors of the 41+ states. Isotopically enriched Te targets were excited by 198-205 MeV 58Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.

Level Scheme of 102In first observed

Neutron deficient nuclei close to 100Sn have been investigated in-beam by particle and γ-ray spectroscopic methods using the NORDBALL detector array following the bombartment of a 54Fe target with a beam of 270 MeV 58Ni. Protons and α particles were identified with a 4π ΔΕ-type Si-multidetector and neutrons with a 1π liquid-scintillator-detectorassembly placed in the forward derection. Excited states of 102In were identified for the first time. The level scheme constructed from γ-γ-particle-coincidence and γ angular correlations is discussed and compared to the structure of neighboring nuclei in the framework of the nuclear shell model.

Nickel ion beam induced modifications in Cu–Se heterojunction nanowires

This paper investigates the properties of Copper–Selenium heterojunction nanowires before and after implantation. Heterojunction between Cu and Se was formed using the template method, assisted by chronoamperometry technique. Implantation in heterojunction nanowires was performed with 80 MeV Ni6+ ions for different fluencies ranging from 1 × 1011 to 1 × 1013 ions/cm2. XRD studies show that no peak shifting takes place after implantation, but a significant variation in peak intensity was observed. Plane orientation and increased crystal quality may be the probable cause for variation in plane intensity. UV–Visible study for optical behavior shows a red shift in the absorption edge along with a decrease in the optical band gap. I–V measurements before and after implantation revealed an increase in the rectification behavior of Schottky junction, which may be due to the interface smoothing and a decrease in junction barrier height during implantation.

Investigation of the mechanical and microstructural evolution of a Cu based bulk metallic glass during ion irradiation

Ion irradiation and annealing experiments were performed on Cu60Zr20Hf10Ti10 bulk metallic glass (BMG) specimens to investigate their irradiation- and temperature-induced microstructural and mechanical property evolution. For the ion irradiations, samples were exposed to 9 MeV Ni3+ ions to a midrange (~1.2 μm depth) dose of 10 displacements per atom (dpa) at temperatures ranging from room temperature to 360 °C (the corresponding peak dose at ~2.8 μm depth was ~25 dpa). Bulk X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization revealed that the alloy did not crystallize during irradiation up to 290 °C but did partially crystallize at 360 °C. XRD analysis revealed that the crystallization which occurred in the sample irradiated at 360 °C was caused by thermal effects instead of irradiation displacement damage. Subsequent Rietveld refinement analysis of the XRD measurements revealed the presence of two distinct crystal phases, namely a CuTiZr hexagonal structure belonging to the P63/mmc space group and a CuTi tetragonal structure belonging to the P4/mmm space group. Nanoindentation experiments revealed that no pronounced hardness changes occurred in the specimens irradiated at room temperature and 290°C, although significant hardening was observed in the sample irradiated at 360 °C. The significant increase in the hardness at 360°C was ascribed to thermally induced partial crystallization of the alloy instead of the ion irradiation. In general, the results of the nanoindentation experiments and XRD characterization suggest that although the Cu BMG exhibits good stability during irradiation at temperatures up to 290 °C it is not suitable for irradiation environments where the temperature is 360 °C for extended periods of time. The Lam and Chong extrapolation method, which has been used to study the indentation size effect (ISE) in amorphous alloys, was employed to quantify how irradiation and temperature affect this type of behavior in the BMG. However, the poor linear fitting of the indentation hardness data by this model indicate that a new ISE model is likely needed to quantify indentation hardening in BMGs.

Ion irradiation stability of oxide nano-particles in ODS alloys: TEM studies

Oxide Dispersion Strengthened (ODS) steels are considered as promising materials for structural components of advanced fusion and fission reactors. Its performance is largely determined by particle size and stability of the dispersed oxide nano-particles which forms during high temperature extrusion after dissolution of yttria in Fe during mechanical alloying. As the reactor structural materials are exposed to high neutron flux, study of irradiation stability of these particles is very important. In order to study irradiation stability of oxide particles in ODS alloy, two different ODS alloys of composition Fe-0.2Ti-0.3Y2O3, Fe–14Cr-0.2Ti-0.3Y2O3 were irradiated using 5 MeV Ni2+ ion beam to 150 dpa at 700 °C and 600 °C at JANNUS irradiation facility giving a dose of 40 dpa at the surface. In order to study the evolution of the nano oxide particles, the irradiated samples were examined using transmission electron microscopy (TEM). A drastic reduction in particle size along with an increase in particle density was observed in the Fe–14Cr-0.2Ti-0.3Y2O3 alloy irradiated up to 40 dpa at 700 °C as compared to 600 °C. The average size reduced from 4 nm (in as-prepared alloy) to 1 nm size. In Fe-0.2Ti-0.3Y2O3 alloy too, particle size reduction was observed upon irradiation at 700 °C, 40 dpa. The observations indicate that the nucleation of oxide particles in Fe matrix occurs along with inverse Oswald ripening.