Investigation of the thermal and neutron irradiation response of BAM-11 bulk metallic glass

Abstract Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) bulk metallic glass was irradiated by neutrons to a fluence of 1.4 × 1020 n/cm2 (E > 0.1 MeV) (0.1 displacements per atom, dpa) at a temperature of ∼70 °C and then analyzed using multiple mechanical property and structural characterization techniques. Nanoindentation hardness measurements revealed that irradiation led to softening and a reduced Young's modulus in the alloy while annealing at 300–325 °C caused an increase in the hardness and modulus. Neutron diffraction results indicated that primary knock-on events caused rejuvenation (structural disordering) while annealing resulted in structural relaxation. Furthermore, it was found that annealing after irradiation reversed the disordering effects caused by the irradiation. The increased disordering in the alloy during irradiation is thought to be attributed to the enhanced free volume content caused by the neutron collision cascades in the matrix. Indeed, immersion density measurements revealed that irradiation led to a decrease in the density of the alloy. This decrease in the macroscopic density was linked to an increase in the structural disorder of the alloy while an increase in the density corresponded to an increasing degree of order. Additionally, synchrotron X-ray diffraction related the structural relaxation of the alloy to a loss of ductility, which is in agreement with the literature. Overall, an increase in the structural disorder in the sample is linked to a softening of the alloy and to a higher concentration of soft-zone defects in the glass.