Radiation induced hardening of beryllium during low temperature He implantation

Journal article

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).

Authors: Kuksenko, V; Lunev, A; Darnbrough, E; Densham, C; Hurh, P

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Journal of Nuclear Materials
• Volume: 555
• Article number: 153130
• Publication date: 2021-06-08
• Acceptance date: 2021-06-02
• DOI: 10.1016/j.jnucmat.2021.153130
• EISSN: 1873-4820
• ISSN: 0022-3115
• Language: English
• Keywords: TEM; helium implantation; dislocation loops; beryllium; irradiation induced hardening; anisotropy