Effects of irradiation spectrum on the microstructural and mechanical properties of bulk metallic glasses

Abstract

Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) and Cu60Zr20Hf10Ti10 bulk metallic glass (BMG) specimens were ion irradiated to characterize and compare their irradiation induced microstructural and mechanical property evolution. For the ion irradiations, samples of each BMG were exposed to 9 MeV Ni3+ and 5.5 MeV C+ ions to a midrange (∼1.5 μm depth) dose of 0.5 displacements per atom (dpa) at temperatures ranging from room temperature to 360 °C in order to examine potential effects associated with low (5.5 MeV C) and high (9 MeV Ni) average primary knock on energies. BAM-11 BMG samples were also irradiated by neutrons (E > 0.1 MeV) at ∼70 °C to a fluence of 1.4 × 1020 n/cm2 (dose of 0.1 dpa). Importantly, no pronounced irradiation spectrum effects were observed for the nanoindentation mechanical properties of the two BMGs following ion irradiation. However, significant softening was observed in the BAM-11 BMG sample irradiated by neutrons, while annealing of the unirradiated samples led to a marked increase in hardening. Results of the nanoindentation experiments indicate that softening is caused by irradiation induced creation of free volume defects, while the hardening is caused by their annihilation.