Internal Friction Measurements on Neutron- Irradiated Fe-3.48% Ni Alloy

The Snoek peak and the strain-amplitude dependence of internal friction were measured in order to gain further information on the behavior of interstitial solute atoms in Fe-3.48%Ni alloy which had been neutron-irradiated and annealed. This alloy contained 37 ppm N and 7 ppm C.

Interstitial solute N and C atoms were trapped by irradiation-induced defects and released by annealing at above 250°C. The Snoek peak and the slops of Granato-Lücke plots which latter is proportional to 1/L_c (L_c being the dislocation loop length between impurity atoms) increased with annealing temperature.

The binding energy of interstitial solute N atoms to dislocations in the irradiated and annealed specimen was obtained from the strain-amplitude dependent internal friction. The value was about 16, 500 cal/mol.     

The effect of irradiation and post-irradiation annealing on the yield stress and microstructure of vanadium-carbon alloys

Vanadium and vanadium-carbon alloys containing 0.15, 0.3 and 1 at% carbon were irradiated in JMTR with fast neutrons (E_n > 1 MeV) at 773 K to a dose of 5 × 10²⁴n/m². Tensile test and microstructural observations were carried out after irradiation and post-irradiation annealing. All of the. specimens showed radiation hardening. The irradiation produced voids, dislocations and radiation-induced quasi-carbides, which were formed by the agglomeration of vacancies and carbon atoms. The radiation anneal hardening in the alloys occurred at 873 K. The void number densities in the alloys had a peak at 873 K while the quasi-carbides decomposed at the same temperature. Therefore, invisible voids existing in the as-irradiated condition would grow by absorbing the vacancies, which were released in the process of decomposition of the quasicarbides during annealing, and the increase of the visible voids would effectively contribute to the radiation anneal hardening of these alloys.     

Electrical properties of annealed, fully metamict REE2FeBe2Si2O10

The electrical properties of annealed, fully metamict gadolinite REEFe²⁺Be₂Si₂O₁₀ are studied as a function of annealing temperature. Changes due to annealing are also probed by ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction. The electrical conductivity measured at f = 100 Hz between 110 and 750 K varies markedly, ranging from 10⁻¹⁰ to 10⁻⁶ S m⁻¹ for untreated samples and 10⁻⁹ to 10⁻³ S m⁻¹ for sample annealed in argon at 1373 K. Average measured activation energies for electrical conduction are 0.47 and 0.63 eV for ranges of 400-450 K and 500-600 K, respectively. The dielectric permittivity shows strong dispersion effects above 235 K. After high temperature annealing, the electrical conductivity shows a marked dispersion below 604 K. The combination of polaron hopping and hydroxyl anion migration is proposed for the electrical conduction mechanism.     

Precision dilatometer analysis of neutron-irradiated nuclear graphite recovery process up to 1673 K

Specimens of two kinds of isotropic nuclear graphite, IG-110U and ETP-10, were neutron-irradiated at fluence of 1.92 × 10²⁴ n/m² (E > 1.0 MeV) at 473 K. The recoveries of the macroscopic lengths of these specimens during isothermal and isochronal annealing at temperatures of up to 1673 K were investigated in a step-wise manner by using a precision dilatometer. The macroscopic lengths after isochronal annealing for 6 h at each temperature decreased gradually as the temperature was increased to 1673 K. The recovery trends of the c-axis and a-axis lattice parameters differed from one another, and from the macroscopic length recovery trends. For the IG-110U specimen, the activation energies (E_a) of macroscopic volume recovery corresponding to annealing at 523–773, 773–923, 923–1073, and 1073–1173 K were found to be 0.15, 0.34, 0.73, and 2.59 eV, respectively. For the ETP-10 specimen, the E_a corresponding to 523–923, 923–1223, and 1223–1373 K were determined to be 0.15, 0.46, and 2.19 eV, respectively. These results indicate that both graphite specimens underwent three or four stages of macroscopic length recovery between 523 K and the annealing temperatures at which their initial lengths were recovered. It is suggested that during the first stage recovery proceeded via the migration of single interstitials along the basal plane and the resulting V-I recombination. In the middle stages, recovery occurred due to the migration of interstitial groups such as C₂ along the basal plane, while in the last stage, it proceeded via through-layer migration of interstitials or migration of single vacancies.     

The influence of the microstructure evolution on the surface morphology in the annealing process of helium-implanted spinel

Single-crystalline spinel (MgAl₂O₄) specimens were implanted with helium ions of 100 keV at three successively increasing fluences of (0.5, 2.0 and 8.0) × 10¹⁶ ions/cm² at room temperature. The specimens were subsequently annealed in vacuum at different temperatures ranging from 500 to 1100 °C. Different techniques, including Fourier transformed infrared spectroscopy (FTIR), thermal desorption spectrometry (TDS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the specimens. It was found that the absorbance peak in the FTIR due to the stretching vibration of the Al-O bond shifts to smaller wave numbers with increasing fluence, shifting back to larger wave numbers with an increase of annealing temperature. The absorbance peak shift has a linear relationship with the fluence increase in the as-implanted state, while it does not have a linear relationship with the fluence increase after the annealing process. Surface deformation occurred in the specimens implanted with fluences of 2.0 and 8.0 × 10¹⁶ ions/cm² in the annealing process. The phenomena described above can be attributed to differences in defect formation in the specimens.     

Effect of helium on the deformation mode for Ti-7.5AI alloy

The effect of helium on the mechanical properties of Ti-7.5Al alloy was investigated at 873 K on the specimens injected with helium to the concentration C_He of 5, 18 and 30 appm by using a cyclotron. Helium had a small effect on the yield stress but a large one on the elongation; the elongation decreased at first with increasing C_He in the region of C_He less than 18 appm and increased again for larger C_He. Correspondingly, the deformation mode changed with the helium concentration. The deformation of uninjected specimens proceeded by the dislocation slip and two twin systems, that is, (101̄2)〈101̄1̄〉 and (112̄1)〈112̄6〉. The latter twin system disappeared in the 18 appm helium-injected specimen. Both deformation twins disappeared in the 30 appm specimen, the microstructure of which exhibited the uniform cellular structure of dislocations.     

Microstructure of helium-implanted Nimonic PE16

Transmission electron microscopy has been used to investigate the microstructure in Nimonic PE16 after room temperature α-implantation followed by subsequent annealing. Helium bubble formation in the matrix, at dislocations, at grain boundaries and at precipitates of γ', M₂₃C₆, and MC type has been studied.     

Enhanced defects recombination in ion irradiated SiC

Point defects induced in SiC by ion irradiation show a recombination at temperatures as low as 320 K and this process is enhanced after running current density ranging from 80 to 120 A/cm².Ion irradiation induces in SiC the formation of different defect levels and low-temperature annealing changes their concentration. Some levels (S₀, S_x and S₂) show a recombination and simultaneously a new level (S₁) is formed.An enhanced recombination of defects is besides observed after running current in the diode at room temperature. The carriers introduction reduces the S₂ trap concentration, while the remaining levels are not modified. The recombination is negligible up to a current density of 50 A/cm² and increases at higher current density. The enhanced recombination of the S₂ trap occurs at 300 K, which otherwise requires a 400 K annealing temperature. The process can be related to the electron-hole recombination at the associated defect.     

Surface damage of metallic glasses by argon ion bombardment

The surface damage of metallic glasses Fe₄₀Ni₄₀P₁₄B₆, Fe₄₀Ni₃₈Mo₄B₁₈, Fe₄₀Ni₄₀B₂₀, Fe₈₀B₂₀ and Ni₆₄Zr₃₆ under argon ion bombardment at room temperature has been investigated. Blister formation was observed in the dose range of 1 × 10¹⁷ to 1 × 10¹⁸ ions/cm². At higher doses, blisters disappeared with concurrent roughening of the bombarded surface. Erosional features like cones and pyramids are not observed. Argon induced blisters also disappeared on room temperature aging without any further bombardment after blister formation. Post-irradiation annealing at high temperatures (673 and 873 K) resulted in blister formation, severe surface exfoliation and pin-hole formation. The precipitation of the implanted argon into bubbles is also observed.     

Pic de relaxation associe aux interstitiels intrinseques dans le zirconium deforme a basse temperature

Internal-friction measurements carried out at three widely different frequencies (≈1, 16 and 350 Hz) have allowed the detailed study of a damping peak in zirconium deformed at low temperature and not allowed to warm up beyond ?68°C. The values obtained for the activation energy and the frequency factor (respectively $\text{0,27 ± 0.02}$ eV and $\text{10}{}^{\mathrm{13\pm 0.8}}\text{sec}{}^{\mathrm{?1}}$), the narrowness of the peak — which allows it to be defined in terms of two simple relaxation times — and the fact that disappearance of this peak at ?68°C is not directly consistent with a dislocation-pinning mechanism, lead to the postulate of a relaxation mechanism involving point defects of a paired oxygen self-interstitial type formed during low-temperature deformation.     

Annealing behavior of krypton-implanted aluminum: I. Diffraction effects from krypton bubbles

Thin aluminum foils, implanted with krypton ions at an energy of 50 keV with a dose of 10¹⁶ ions/cm², have been investigated by the analysis of electron diffraction patterns. The spots due to double diffraction are observed at room temperature and are interpreted to originate from the well isolated solid krypton bubbles. During annealing, these spots remain up to around 483 K, while the diffraction from solid krypton disappears just above 618 K, indicating the melting of solid bubbles. Streaks in the diffraction patterns are also observed above 618 K. It is demonstrated that the streaks are caused by the growth of microcracks in the specimen.     

Response of synthetic coffinite to energetic ion beam irradiation

Coffinite, USiO₄, is one of the two most abundant and important naturally occurring U⁴⁺ phases (the other is UO₂), and it is an alteration product of the UO₂ in spent nuclear fuel when in contact with silica-rich groundwater under reducing conditions. Despite its ubiquity, there are very limited data on the response of coffinite to radiation. Here, we present the results of the first systematic investigation of energetic ion beam irradiation (1 MeV Kr²⁺) of ultra-fine, synthetic coffinite (20-50 nm). In situ transmission electron microscopy (TEM) showed that the crystalline-to-amorphous transformation occurs at a relatively low dose, ∼0.27 displacements per atom (dpa) at room temperature. The critical temperature, T_c, above which coffinite cannot be amorphized, is low (∼608 K). Synthetic coffinite is more stable as compared with isostructural zircon (ZrSiO₄; T_c = 1000 K) and thorite (ThSiO₄; T_c above 1100 K) upon ion beam irradiation at elevated temperature, suggesting enhanced defect annealing behavior in nano-sized synthetic coffinite. Irradiation was found to decrease the temperature required to induce phase decomposition process in coffinite upon thermal annealing. A good correlation among the critical amorphization temperature, T_c, phase decomposition temperature, T_f, and the temperature range of the two-phase (ZrO₂ and SiO₂) co-existed region was identified.     

Depth dependent damage profile in stainless steel irradiated with He-ions

Type 316 stainless steel was irradiated with 24 MeV He-ions up to 3.2 × 10²⁰ ions/m² at ambient temperature. A peak in microhardness occurred at a distance of 105 μm from the irradiated surface. Small dislocation loops were seen at depths ranging from 105 to 114 μm with the peak in number density at 110 μm. A pair of parallel lines with a space of 8 μm centered at a distance of 107 μm from the irradiated surface were revealed on the top surface of the specimen by chemical etching after post-irradiation annealing for l h at 1023 K. The parallel lines correspond to arrays of fairly large Frank loops aligned in narrow bands on each side of a region containing helium bubbles. The observed damage profiles agree with those predicted by Littmark and Ziegler.     

The modified relaxation time function: A novel analysis technique for relaxation processes. Application to high-temperature molybdenum internal friction peaks

The modified relaxation time (MRT) function, which is based on a general linear viscoelastic formalism, has several important mathematical properties that greatly simplify the analysis of relaxation processes. In this work, the MRT is applied to the study of the relaxation damping peaks in deformed molybdenum at high temperatures. The dependence of experimental data from these relaxation processes with temperature are adequately described by a Havriliak-Negami (HN) function, and the MRT makes it possible to find a relation between the parameters of the HN function and the activation energy of the process. The analysis reveals that for the relaxation peak appearing at temperatures below 900 K, the physical mechanism is related to a vacancy-diffusion-controlled movement of dislocations. In contrast, when the peak appears at temperatures higher than 900 K, the damping is controlled by a mechanism of diffusion in the low-temperature tail of the peak, and in the high-temperature tail of the peak the creation plus diffusion of vacancies at the dislocation line occurs.     

Effects of the fabrication process parameters on the precipitates and mechanical properties of a 9Cr-2W-V-Nb steel

The effects of the fabrication process parameters such as a tempering temperature, cold rolling and annealing condition on the precipitates and mechanical properties of a normalized 9Cr-2W-V-Nb steel were evaluated. Nb-rich MX precipitates were found in the specimen tempered at 550 °C while M₂₃C₆, Nb- and V-rich MX ones were observed in the specimen tempered at 750 °C. A cold rolling and an annealing at 750 °C of the specimen tempered at 550 °C induced the formation of large inhomogeneous M₂₃C₆ carbides, causing a reduced tensile strength. However, the cold rolling of the specimen tempered at 750 °C provided fine precipitates due to a fragmentation of some of the M₂₃C₆ carbides, and an annealing at 700 °C for 30 min was found to be suitable to recover the degraded mechanical properties from a cold working.     

Thermal Recovery of Radiation Defects and Microstructural Change in Irradiated UO2 Fuels

Abstract

Thermal recovery of radiation defects and microstructural change in UO₂ fuels irradiated under LWR conditions (burnup: 25 and 44 GWd/t) have been studied after annealing at temperature range of 450-1,800°C by X-ray diffractometry and transmission electron microscopy (TEM). The lattice parameter of as-irradiated fuels increase with higher burnup, which was mainly due to the accumulation of fission induced point defects. The lattice parameter for both fuels began to recover around 450-650°C with one stage and was almost completely recovered by annealing at 850°C for 5 h. Based on the recovery of broadening of X-ray reflections and TEM observations, defect clusters of dislocations and small intragranular bubbles began to recover around 1.150–1,450°C. Complete recovery of the defect clusters, however, was not found even after annealing at 1,800°C for 5h. The effect of irradiation temperature on microstructural change of sub-grain structure in high burnup fuels was assessed from the experimental results.     

Mechanical properties of molybdenum neutron-irradiated at a high temperature

Molybdenum specimens prepared by two processes, powder-metallurgy (PM) and electron-beam melting (EB), were irradiated to a fast neutron fluence of 2.74 × 10²⁴n/m² (E_n? 1 MeV) at about 600°C (873 K), and their mechanical properties were studied in detail. It was shown that the degree of irradiation embrittlement in EB-Mo was smaller than that in PM-Mo, which might be caused by stronger grain-boundaries and probably smaller irradiation-hardening in the former. From the relation between the recovery of ductility and microstructural changes in post-irradiation annealed PM-Mo at 800 (1073 K), 1000 (1273 K) and 1200°C (1473 K), it was concluded that the recovery resulted from a decrease of irradiation hardening due to a rearrangement and a disappearance of depleted-zones, dislocation-loops and voids in order with increasing annealing temperature. An anomalous mode of fracture was observed in as-irradiated specimens, which consisted of inhomogeneous deformation, then brittle fracture not at the center but at the root of the deformation neck. This mode was observed in a narrow temperature range near the DBTT. A possible mechanism is discussed.     

Irradiation growth in deformed zirconium

Single crystals and polycrystals of pure zirconium were irradiated at 353 K and 553 K with fast neutrons to fluences up to 8.1 × 10²⁵ n/m² to determine the effects of various deformation-induced defect structures on irradiation growth. An a-axis single crystal that was swaged 18% grew linearly at a very high rate (˜1.4 × 10⁻²⁸ m²/n) as a result of the massive aligned twins and dislocations (with a-type and c-component Burgers vectors) introduced by deformation. Annealing the swaged crystal at 673 K for 1 h prior to irradiation resulted in a much lower growth rate due to the recovery of the dislocation structure generated by deformation. Annealing the swaged crystal at 823 K instead also retarded growth but to a lesser extent. Grain boundaries, caused by partial recrystallization, were found in the 823 K specimen only and were believed to be responsible for the observed effect. An a-axis crystal that was strained 5% in tension showed little change in length, suggesting that the effect of a small increase in a-type dislocations is relatively minor. Growth was suppressed in the polycrystalline zirconium specimens that were pulled 5%. This is attributed to radiation-enhanced stress relaxation. It also confirms that a high dislocation density is essential to giving a high growth rate in zirconium.     

The effects of the annealing time on helium implantation in Si

The modifications induced in silicon samples by helium implantation before and after isothermal annealing at 673 K have been investigated. The surface morphology has been detected by atomic force microscopy. A hillock structure is observed on the sample surface before and after annealing for 5-10 min. Surface blister formation is observed with an increasing annealing time. The variation of crystal damage with annealing time has been investigated by Rutherford backscattering/channeling. The intensity of the damage peak first increases with annealing time, reaches maximum at an annealing time of 60 min and then decreases. Helium-induced bubbles and residual defects have been observed by transmission electron microscopy, which shows that dislocations are close to the bubbles.