Radiation induced hardening of beryllium during low temperature He implantation

[摘要] 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 degrees C and 200 degrees C. 11 different energies were used, so as to create a quasi-homogeneous 3 mu m irradiated layer with average radiation damage of 0.1 dpa and average He content of 20 00 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 degrees C irradiation and 10 0% for the 50 degrees 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 [0 001] 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 degrees C and 100% after irradiation at 200 degrees 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 similar to 10(22) 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). (C) 2021 The Authors. Published by Elsevier B.V.

[发布日期] 2021-11-01

[关键词] Beryllium;Helium implantation;Irradiation induced hardening;Anisotropy;TEM;dislocation loops