Experimental investigation of helium migration in an fcc aluminum matrix

Experimental investigation of helium migration in an fcc aluminum is reported. A pure aluminum with 0.15 wt% of ¹⁰B was neutron-irradiated to obtain (1.2 ± 0.2) × 10²⁴ m^-3 helium atoms in the metal according to the reaction ¹⁰B + n → ⁷Li + ⁴He. The post-irradiated metal was observed in situ in TEM while the sample was heated to 470 °C with a hot stage holder. A helium-rich area was found in the vicinity of nanometric ¹⁰B segregates that were not solute in the aluminum. The helium-rich area was characterized as a polygonal faceted region. According to EELS measurements, this area is saturated with N_He = (3 ± 1) × 10²⁸ m^-3 helium atoms, which are (30-65)% of the atoms in the observed area. It was found that the helium-rich area expands due to helium migration. Electron beam diffraction revealed that the preferred orientation of the helium atoms' migration is normal to plane (0 over(2, -) 2). The results are consistent with models for helium atoms migration between interstitial sites for an fcc metal.