Search

• Helium implantation resulted in significant hardness increase of beryllium. • Dislocation loops and helium bubbles are responsible for hardening. • Low purity grade has higher irradiation induced hardening after 200°C implantation. • Crystallography leads to significant scatter in indentation hardness. • Softer grains exhibited higher irradiation induced hardening. The effect of ion irradiation on evolution of microstructure and hardening of beryllium with different impurity levels was investigated using TEM and nanoindentation. High purity S-65 grade and less-pure S-200-F grade were implanted by helium ions at temperatures of 50°C and 200°C. 11 different energies were used, so as to create a quasi-homogeneous 3 µm irradiated layer with average radiation damage of 0.1 dpa and average He content of 2000 appm. Nanoindentation experiments demonstrated that before irradiation, the S-200-F and S-65 grades have an average hardness of 3.7±0.8 GPa and 3.4±0.8 GPa correspondently. After implantation the hardness of both grades increased by about 60% for the 200°C irradiation and 100% for the 50°C irradiation. The crystallographic analysis of indented grains demonstrated that in the as-received materials the hardness is about 2.5 times higher when the indentation direction is close to the [0001] c-axis of beryllium compared to indentation perpendicular to [0001]. Hardness anisotropy significantly decreased after irradiation: the "soft orientation" was most sensitive to irradiation-induced hardening, with hardness increasing by about 140% after irradiation at 50°C and 100% after irradiation at 200°C, compared to about 15 - 20% for the "hard" orientation at both irradiation temperatures. The higher purity grade had smaller increase of the "soft orientation" hardness: 2.5±0.3 GPa for the S-65 and 2.9±0.2 GPa for the S-200-F. At both temperatures in both grades, under TEM investigation the radiation damage appears as "black dots" which are likely to be small dislocation loops with the number density of ~ 1022 m−3. No bubbles were observed by TEM inside grains and at grain boundaries. Analysis of the possible hardening contribution demonstrated that the observed "black dots" could be responsible for up to half of the measured hardening, while the rest of the hardening should originate from helium bubbles with the size below the TEM resolution (at or below 1.5 nm). [ABSTRACT FROM AUTHOR]

Multiple length-scale microstructural characterisation has been conducted on four different grades of unirradiated fine-grained graphite: CL 2020, IG 430, SGL R7650 and POCO ZXF-5Q, which are the potential candidates as high-power proton beam intercepting materials (secondary particle-production targets). Micrometre and sub-micrometre sized porosity structures have been characterised by X-ray micro-computed tomography (µXCT) and focused ion beam-scanning electron microscopy tomography (FIB-SEM tomography). Results show that these four grades of graphite have distinct porosity structures with a substantial amount of interconnected pores; POCO-ZXF-5Q has the most uniform porosity size and spatial distribution out of the four at these length scales examined. As a direct measurement of the total number and volume of nano-sized Mrozowski cracks is currently not readily feasible, the characteristic crystalline size L a reflecting the coherent scattering length at nano-scale was evaluated using micro-Raman spectroscopy. It has been found that a significant reduction in average characteristic crystalline size had been induced by sample preparation. Further measurements on freshly fractured sample surfaces excluding these damages suggested that IG430 graphite has the largest average crystallite size (~290 nm) while POCO-ZXF-5Q has the smallest average crystallite size (~80 nm) with a narrow distribution. These results from un-irradiated graphite were used to further understand the proton irradiated behaviour of these four grades of graphite. [ABSTRACT FROM AUTHOR]

For the advancement and development of nuclear systems used in heavy irradiation environments such as fusion DEMO reactors, fission reactors, fast reactors, and accelerator driven target systems, it is necessary to fully understand the changes of mechanical properties and the other properties of the materials induced by irradiation and to clarify the synergistic effect of displacement damage and helium generation. In this study the mechanical property changes and microstructural development induce by displacement damage and helium production have been mainly examined in austenitic stainless steels, 316FR and type304, and ferritic/martensitic steel, HCM12A, irradiated at around 550oC in JRR-3M reactor and/or JOYO fast reactor. At 550°C, 316FR steel was superior to 304 steel in terms of the amount of ductility and strength with respect to irradiation resistance. It is noteworthy that at 550 °C as well as room temperature, the higher fracture strength of the 316FR steels is a remarkable result. It is found that helium atoms strongly influenced on creep lifetime of the irradiated austenitic stainless steel, 316FR. It was found that the ratio of creep rupture time is slightly lower than the lower limit of previous study's Miyaji and co-workers in the region from 0.01 appm to 1 appm. It is also found that the lower limit of reduction ratio of creep rupture time (irradiation specimen to unirradiation one) does not decrease linearly with the helium production above 10 appm up to about 33 appm. dpa enhanced the reduction of creep lifetime. Recent R&D of high-energy accelerator driven target systems used under heavy irradiation environment is also introduced and discussed for high radiation resistance materials such as Ti alloys with very high number density of nano size precipitate, which have been studying under RaDIATE collaboration, from points of view of irradiation damage and materials development. [ABSTRACT FROM AUTHOR]

l High intensity proton beam irradiation on dual-phase titanium alloys up to 0.25 dpa l Modest work hardening capability remains for Ti-3Al-2.5V while none for Ti-6Al-4V l High-density defect clusters in α grains and nano-scale ω-phase precipitation in β l Radiation-induced ω-phase could lead to greater loss of ductility for Ti-6Al-4V A high-intensity proton beam exposure with 181 MeV energy has been conducted at Brookhaven Linac Isotope Producer facility on various material specimens for accelerator targetry applications, including titanium alloys as a beam window material. The radiation damage level of the analyzed capsule was 0.25 dpa at beam center region with an irradiation temperature around 120 °C. Tensile tests showed increased hardness and a large decrease in ductility for the dual α+β-phase Ti-6Al-4V Grade-5 and Grade-23 extra low interstitial alloys, with the near α-phase Ti-3Al-2.5V Grade-9 alloy still exhibiting uniform elongation of a few % after irradiation. Transmission Electron Microscope analyses on Ti-6Al-4V indicated clear evidence of a high-density of defect clusters with size less than 2 nm in each α-phase grain. The β-phase grains did not contain any visible defects such as loops or black dots, while the diffraction patterns clearly indicated ω-phase precipitation in an advanced formation stage. The radiation-induced ω-phase transformation in the β-phase could lead to greater loss of ductility in Ti-6Al-4V alloys in comparison with Ti-3Al-2.5V alloy with less β-phase. Image, graphical abstract [ABSTRACT FROM AUTHOR]