An exploratory study on helium mobility in amorphous and crystallized bulk metallic glasses

Zr52.5Cu17.9Ni14.6Al10Ti5 and Cu60Zr20Hf10Ti10 amorphous and crystallized bulk metallic glasses (BMGs) were implanted at room temperature by 150 keV He-3(+) ions to fluences of 2 x 10(15) cm(-2) and 5 x 10(15) cm(-2), producing peak implanted He concentrations of similar to 1,100 and 3,500 appm, respectively. Nuclear reaction analysis (NRA) performed on post-implantation annealed samples at various temperatures between 250 and 600 degrees C (similar to 0.30 to 0.75 of the absolute melting temperature T-m of the BMGs) revealed no appreciable He migration. Complementary thermal desorption spectroscopy (TDS) on as-implanted samples, which involved in situ annealing, showed appreciable He release only at temperatures higher than similar to 700 degrees C (similar to 0.76-0.90 T-m) in all the samples. Half or more of the implanted He did not desorb up to the maximum investigated TDS annealing temperature of 770 degrees C (similar to 0.85-0.97 T-m). The lack of pronounced He diffusion up to 600 degrees C as observed from the NRA and TDS data was attributed to He trapping in free volume sites present in the BMGs, which seems to play a similar role to vacancies in crystalline materials. It was also observed that in both the amorphous and crystallized forms of the Zr BMG, the sample implanted to the lower fluence released more He as compared to the sample implanted with a higher fluence. The crystalline forms of both the Cu and Zr BMGs released more He as compared to their amorphous counterparts. (C) 2020 Elsevier B.V. All rights reserved.