Search

Atom probe tomography (APT) and selected area electron diffraction (SAED) by transmission electron microscopy (TEM) were applied to nano-scale precipitates formed in a neutron-irradiated iron (99.99% pure) at high temperatures. In the conventional TEM, we discovered donut-type precipitates on the {100} planes that formed at the dilatational side of interstitial type dislocation loops with the Burgers vector of <100> on the habit planes of {100} in the bcc iron lattice. The precipitates were identified as nitride, bct α″-Fe16N2, by chemical composition and lattice structural analyses using APT and SAED. Image contrasts of the α″-Fe16N2 in a weak beam dark-field electron microscopy study were carefully analysed with the diffraction vector and the sign of deviation parameter from the Bragg condition, and it was concluded to be a selective visualisation of α″-Fe16N2 on one of the {100} planes. These results were in agreement with the crystallographic orientation between the α″-Fe16N2 and matrix iron, thereby bridging a knowledge gap in α″-Fe16N2 formation during neutron irradiation using a sodium-cooled experimental fast reactor, JOYO, or a 14 MeV D-T neutron source, RTNS-II. [ABSTRACT FROM AUTHOR]

We conducted systematic experiments of defect structure development in Cu base binary alloys under 1000 kV electron irradiation at temperatures higher than 300 K, usingin situobservations with high voltage electron microscopy. This report describes the effects of undersize elements: Co (–3.78%), Ni (–8.45%) and Be (–26.45%). The volume size factors are given in parentheses. The amounts of the respective elements were 2, 0.3, 0.05 at.%, or less. In Cu–Ni and Cu–Co and in the reference Cu, temperature dependence of the number density of interstitial-type dislocation loops had a down peak (i.e. loops hardly formed) at approximately 373 K, attributed to unexpected impurity atoms. Above the down-peak temperature, the addition of Co or Ni increased the loop number density through continuous nucleation of loops, extended the loop formation to higher temperatures, and decreased the apparent activation energy of loop growth rate. The addition of Be for 0.3 at.% or more delayed loop formation after formation of stacking fault tetrahedra (SFTs) around 300 K. The apparent mobility of self-interstitial atoms is expected to be smaller than that of vacancies because of strong binding with Be. Loop formation at temperatures higher than 373 K was enhanced by Be for 0.3 or 2 at.%, although it was suppressed greatly for 0.05 at.% or less. All undersize atoms increased the stability of SFTs under irradiation. Mechanisms of those effects were discussed and were briefly compared with earlier results found for oversize elements in Cu. [ABSTRACT FROM AUTHOR]

He and H can be produced by nuclear reaction. In addition, energetic particles of He and T and D, which are isotopes of H, in the plasma of fusion reactor induce the damage in the surface of materials, such as erosion, sputtering and blistering. To investigate the interaction of He and D, amorphous and crystalline FeBSi alloys were irradiated by He or D2or He + D2ions with 5 keV. The results of thermal desorption indicated that more He atoms were trapped in both the amorphous and crystalline alloy irradiated by He ions than D atoms in those alloys irradiated by D2ions. Although He and D atoms were trapped in FeBSi alloy irradiated by He + D2ions, desorption peaks of D2and He were separated. Absorption of D in an amorphous alloy was influenced by the presence of He; however, absorption of He was independent of D2irradiation in both alloys. [ABSTRACT FROM AUTHOR]

The defect structures in Ni, Fe–15Cr–16Ni and Ti-added modified SUS316SS (modified SUS316) were examined after neutron irradiation below 0.3 dpa by the Japan Materials Testing Reactor and Belgian Reactor 2 to compare their defect structural evolution. The growth behaviour of interstitial-type dislocation loops (I-loops), stacking fault tetrahedra (SFTs) and voids was found to be quite different among these specimens. I-loops developed at lower temperatures in Ni than in Fe–15Cr–16Ni and modified SUS316, and more swelling occurred in Ni than in Fe–15Cr–16Ni. Finally, there were no voids in modified SUS316. These results were analysed in terms of the I-loop energy. A large discrepancy was found between the analytical results and experimental observations for Ni and modified SUS316, which suggests the formation of unfaulted I-loops directly from collision cascades. The growth of SFTs was detected in Fe–15Cr–16Ni and modified SUS316, and can be explained by a change in the dislocation bias of SFTs resulting from the absorption of alloying elements. [ABSTRACT FROM AUTHOR]

It is interesting to investigate the formation of He bubbles in amorphous alloys because point defects do not exist in amorphous materials. In the present study, the microstructural evolution of amorphous Fe79B16Si5 alloy, either irradiated with 5 keV He+ ions or implanted with 150 eV He+ ions without causing displacement damage, and then annealed at a high temperature, was investigated using transmission electron microscopy (TEM). Vacancy-type defects were formed in the amorphous alloy after irradiation with 5 keV He+ ions, and He bubbles formed during annealing the irradiated samples at high temperature. On the other hand, for samples implanted with 150 eV He+ ions, although He atoms are also trapped in the free volume, no He bubbles were observed during annealing the samples even up to 873 K. In conclusion, the formation of He bubbles is related to the formation and migration of vacancy-type defects even in amorphous alloys. [ABSTRACT FROM PUBLISHER]

Helium generated in materials by the nuclear reaction (n, α) is generally considered to be harmful. It is well-known that helium prompts not only the nucleation of interstitial-type dislocation loops, but also the nucleation of voids in metals and alloys irradiated with high-energy particles, which degrades their mechanical properties. In this study, however, we find that helium trapped by dislocations in Ni increases both the ultimate tensile strength and total elongation. [ABSTRACT FROM PUBLISHER]

The formation of Cu precipitates and point defect clusters was investigated in two Fe–Cu binary model alloys, Fe–0.3Cu and Fe–0.6Cu, irradiated at 573 K at three different damage rates, namely 3.8 × 10−10, 1.5 × 10−8 and 5 × 10−8 dpa (displacements per atom)/s, up to about 1.6 × 10−2 dpa. Results of positron annihilation experiments indicated that Cu precipitates were formed in these irradiations with different damage rates. The growth of Cu precipitates does not increase monotonously with increasing irradiation dose, but it rather depends on the nucleation and growth of microvoids. It is also clear that the nucleation and growth of microvoids are influenced by the irradiation dose rate. [ABSTRACT FROM AUTHOR]

Hydrogen in nano-voids in neutron-irradiated nickel has been detected using positron annihilation lifetime spectroscopy (PALS). As positron lifetime is greatly affected by nano-voids bound with hydrogen, special attention was paid to the analysis. The positron lifetime of neutron-irradiated nickel at higher irradiation doses increased with the dose, which is an indicator for vacancy cluster (nano-void) formation in the lattice. The introduction of hydrogen in well-annealed nickel by electrical charging also resulted in an increase in positron lifetime due to vacancy formation. In neutron-irradiated nickel specimens, hydrogen charging shortened the positron lifetime from 456 to 334 ps (irradiation dose: 3 × 10-3 dpa). Isochronal annealing behaviour of hydrogen-charged nickel and neutron-irradiated nickel was also studied. Positron trapping rate was calculated using a simple trapping model. Thermal desorption spectroscopy was used for the investigation of hydrogen behaviour in non-irradiated hydrogen-charged nickel. [ABSTRACT FROM AUTHOR]

The formation and stability of Cu precipitates and point-defect clusters have been investigated in two Fe–Cu binary model alloys irradiated with fission neutrons at temperatures of 573 K and 673 K. The results of positron annihilation experiments indicate that Cu precipitates, microvoids and interstitial-type dislocation loops were formed after a first irradiation step at 573 K. A substantial aggregation of Cu atoms occurred upon irradiation at 673 K following the irradiation at 573 K. In addition, this second irradiation caused the interstitial-type dislocation loops and microvoids that formed as a result of the irradiation at 573 K to shrink and disappear. [ABSTRACT FROM AUTHOR]

Systematic experiments of 1MeV electron irradiation were made on Cu-based binary alloys above 300 K using a high-voltage electron microscope in order to study the effects of solute atoms on defect structure development. The solute elements examined were Si (+5.08%), Ge (+27.77%) and Sn (+83.40%), the volume size factors of which are given in parentheses; the amounts of these were 0.05, 0.3 and 2 at.% respectively. Interstitial-type dislocation loops and stacking-fault tetrahedra (SFTs) were formed in pure Cu and all the alloys. In pure Cu, the temperature dependence of the loop number density had a 'down peak' (i.e. loops hardly formed) around 373 K; below this temperature the majority of the loops shrank and disappeared during irradiation, while all the loops grew larger above it; and SFTs were unstable and repeated the formation and disappearance. In the alloys, the loop number density decreased monotonically with increasing temperature (no down peak was observed); loop formation was greatly enhanced except for complete suppression above certain temperatures in Cu-Ge and Cu-Sn alloys; and stable SFTs formed up to higher temperatures. The mechanisms for these effects were proposed, taking into account the trapping of point defects by solute atoms, the radiation-induced segregation of solute elements, and the bias effect on point-defect absorption at defect clusters owing to the segregated solute elements. [ABSTRACT FROM AUTHOR]