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.