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

Abstract Zr52.5Cu17.9Ni14.6Al10Ti5 and Cu60Zr20Hf10Ti10 amorphous and crystallized bulk metallic glasses (BMGs) were implanted at room temperature by 150 keV 3He+ ions to fluences of 2 × 1015 cm-2 and 5 × 1015 cm-2, producing peak implanted He concentrations of ~1,100 and 3,500 appm, respectively. Nuclear reaction analysis (NRA) performed on post-implantation annealed samples at various temperatures between 250 and 600 °C (~0.30 to 0.75 of the absolute melting temperature Tm 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 ~700 °C (~0.76-0.90 Tm) in all the samples. Half or more of the implanted He did not desorb up to the maximum investigated TDS annealing temperature of 770 °C (~0.85-0.97 Tm). The lack of pronounced He diffusion up to 600 °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.