To investigate the effects of damage rate on irradiation-induced hardening and microstructural evolution, proton irradiation experiments were conducted on Fe-0.05 wt.%Cu binary alloy samples over a wide range of ion fluxes spanning three orders of magnitude. The samples were then subjected to nano-indentation tests and microstructural observations. Nano-indentation hardness tests revealed greater hardening at lower damage rates, even under the same damage level. TEM observation showed that larger but fewer dislocation loops formed under low damage rate conditions, while high damage rates produced smaller but denser dislocation loops. STEM/EDS analysis showed that as the damage rate decreased, the number density and diameter of Cu-rich precipitates increased, and the Cu concentration therein increased. Irradiation hardening contribution was estimated by invoking the dispersed-barrier hardening model and the Russell-Brown model indicating that the effect of damage rate on irradiation hardening controlled by CRPs is dominant. Since kinetic modeling simulation showed enhanced vacancy mobility at lower damage rates and enhanced Cu-rich precipitate formation, it supported the experimental results. Our findings suggest that damage rate has a significant effect on irradiation hardening behavior, and that low damage rate significantly contributes to the nucleation and growth process of Cu-rich precipitates by thermal diffusion during prolonged irradiation.
Damage rate effects have been recognized as being important for understanding the correlation between mechanical property changes and microstructural evolution in neutron-irradiated commercial reactor pressure vessel steels. In this study, the correlation between the irradiation hardening behavior and defect cluster formation in proton-irradiated Fe-Cu model alloy is investigated using nanoindentation tests and transmission electron microscopy with a variety of damage rates for the proton irradiations. A wide range of damage rates across three orders of magnitude is adopted for the proton flux in a single irradiation experimental system. The hardness in the low damage rate case is higher than in the high damage rate case in the initial stage of damage level when hardening behavior was not saturated. From transmission electron microscopy observations, it is found that a low density of large dislocation loops is formed under lower damage rate conditions. According to the irradiation hardening estimation based on the classical dispersed barrier hardening model, it is indicated that the damage rate effects on the hardening contribution are weak for dislocation loops but dominant for Cu-rich precipitates.
The CANDLES-III detector was installed at the Kamioka Observatory in Japan to investigate the double f decay of 48 Ca. This system combines an undoped calcium fluoride scintillator with along attenuation length (larger than 100 cm), and a two-phase liquid scintillator, thereby serving as a larger-mass detector of 305 kg (contains 350 g of 48 Ca) while maintaining a high energy resolution (a = 2 . 6 % at Q-value of 48 Ca double beta decay). Low-background conditions are achieved in the energy region of interest by improving the light yield and collection efficiency of the detector system, allowing to access a high energy resolution, as well as by installing passive and active radiation shielding, and using pulse-shape analysis. This paper describes the details of the detector including its site and data acquisition system and presents its performance characterization.
We investigated the effects of nickel and nickel-based alloys as catalysts to reduce the hydrogen desorption temperatures of magnesium hydride films deposited by magnetron sputtering. We measured the hydrogen desorption spectra of magnesium hydride films with nickel and Ni-Co, Ni-Fe, Ni-Ti, and Ni-Cu alloy catalytic layers by thermal desorption spectroscopy. The chemical composition of the magnesium hydride films was MgH1.7 as determined by elastic recoil detection analysis and X-ray diffraction. MgH1.7 film with a nickel layer (Ni/MgH1.7) showed onset and termination temperatures of hydrogen desorption were 100 degrees C and 178 degrees C, respectively. The onset temperatures of Ni-Co/MgH1.7, Ni-Fe/MgH1.7, and Ni-Ti/MgH1.7 were higher than that of Ni/MgH1.7, which was almost the same as that of Ni-Cu/MgH1.7. To lower the hydrogen desorption temperature, we prepared a multilayer film [Ni/MgH1.7]5 by depositing MgH1.7 and nickel layers alternately five times, but this did not decrease the onset temperature of the multilayer film. On the basis of the experimental results, we discussed a possible mechanism underlying hydrogen desorption from magnesium hydride films with catalytic layers.
The irradiation hardening factor of the cavities (helium bubbles) in tungsten, as the divertor candidate material, in nuclear fusion reactor, has been investigated through an in-situ TEM observation during tensile test. The obstacle barrier strength α has been calculated by the bow-out behavior of a dislocation based on the line tension model. The obstacle barrier strength α of the cavity with a diameter of 2 nm in W has been measured to be 0.53 ± 0.02. The fraction of cross-slip behavior except the obstacle-cutting mechanism owing to the dynamic interaction between a dislocation of screw type and a cavity has been about 11 %. The fraction of cross-slip behavior of the screw dislocation in W has been smaller than those of other BCC structure materials.
