Composition dependence of open-volume relaxation in Zr-Cu-Al bulk amorphous alloys studied by positron annihilation

Structural relaxation behavior of various composition for Zr-Cu-Al ternary bulk amorphous alloys (hyper-eutectic: Zr45Cu45Al10 and Zr49Cu41Al10, eutectic: Zr50Cu40Al10, hypo-eutectic: Zr55Cu35Al10 and Zr60Cu30Al10) during isothermal annealing below glass transition temperature (Tg) has been investigated by positron annihilation techniques (positron lifetime and coincidence Doppler broadening (CDB)), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and bulk density measurements. The annealing makes the positron lifetime decrease owing to the relaxation. However, maximum decreasing of positron lifetime after 10 ks annealing for eutectic alloy was observed. And different composition dependence of positron change between hypo- and hyper-eutectic alloys was confirmed. Especially, open-volume in hyper-eutectic alloys is hard to change by the annealing. We found that the trend of positron lifetime change Δτ with Zr concentration is not necessarily correlated with the change in bulk density consistently. On the other hand, the positron lifetime during annealing obeys a stretched exponential relaxation function. Also we found the relaxation parameter β, which indicates the distribution activation energy for open-volume relaxation, varies in Zr concentration.