Radiation induced hardening of beryllium during low temperature He implantation

Radiation induced hardening of beryllium during low temperature He implantation

Radiation induced hardening of beryllium during low temperature He implantation 150 150 UKAEA Opendata
UKAEA-CCFE-PR(21)15

Radiation induced hardening of beryllium during low temperature He implantation

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 nuclear beryllium grade and lower-pure S-200-F structural beryllium grade were implanted by helium ions at temperatures of 50ºC and 200ºC. 11 different energies were used, so as to create a quasi-homogeneous 3µm irradiated layer with average radiation damage of 0.1dpa and average He content of 2000 appm. At both temperatures in both grades, under TEM investigation the radiation damage appears as “black dots” (<10 nm in diameter) which are likely to be small dislocation loops with the number density of ~ 1022 m-3. No bubbles were observed inside grains and at grain boundaries. Nanoindentation experiments demonstrated that the lower-purity S-200-F grade has higher average hardness (3.7±0.8 GPa) than the S-65 grade (3.4±0.8 GPa) in the as-received and irradiated states. After helium implantation of both grades the hardness increased by 60% for the 200ºC irradiation and 100% for the 50ºC irradiation. The higher purity S-65 grade showed smaller changes in hardness at 200ºC than the less pure S-200-F. Use of EBSD to give the crystallographic orientation of indented grains revealed that in both grades 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 radiation-induced hardening, with hardness increasing by about 140% after irradiation at 50ºC and 100% after irradiation at 200ºC, compared to about 15 – 20% for the “hard” orientation at both irradiation temperatures. Analysis of the possible hardening contribution demonstrated that the “back dots” should lead to about 0.85 and 1.7 GPa hardness increase, while the rest of the hardening should originate from helium bubbles with the size below the TEM resolution (at or below 1.5 nm).

Collection:
Journals
Journal:
Journal of Nuclear Materials
Publisher:
Elsevier