Electron-irradiation induced creep in amorphous alloys

Electron-irradiation induced creep rates in amorphous alloys, a-SiO₂, Fe₇₉B₁₆Si₅, Cu₆₀Ta₄₀, and Cu₅₀Ti₅₀, were measured at room temperature using a miniaturized beam-bending apparatus within a transmission electron microscope operated at 200 keV. The creep rates of these amorphous samples increased nearly linearly with both e-beam current density and applied stress, while a reference crystalline (c-) SiO₂ sample failed to creep under the same conditions. The irradiation-induced creep compliance of a-SiO₂ was 15 times larger than that of Fe₇₉B₁₆Si₅ and over 1, 000 times larger than that of the two Cu alloys. Molecular dynamics computer simulations were employed to simulate electron irradiation induced creep using interatomic potentials representing amorphous Cu₇₅Zr₂₅, Ni₈₅P₁₅, and SiO₂ as model systems. The irradiation induced creep compliances calculated for Cu₇₅Zr₂₅ during 200 keV electron irradiation provided good quantitative agreement with the two Cu-based alloys, but that for a-SiO₂ was 180 times too small. These results indicate that unlike neutron or ion-beam induced creep in a-SiO₂, creep under electron irradiation is dominated by the effects of ionization, owing largely to the far higher ratio of electronic stopping to nuclear stopping for electrons than for ions.