Enhanced thermal stability of Zr₆₅Cu_17.5Ni₁₀Al_7.5 metallic glass at temperature range near glass transition by oxygen impurity

The 'panoramic effects' of oxygen impurity on the thermal stability of Zr₆₅Cu_17.5Ni₁₀Al_7.5 metallic glass have been investigated by constructing time-temperature-transformation diagram and analyzing the precipitation kinetics of primary phase. It is found that oxygen has contrary effects on the alloy's thermal stability exhibiting in high- and low-temperature ranges because of primary phase selection. The primary phase for Zr₆₅Cu_17.5Ni₁₀Al_7.5 glassy alloy depends on its oxygen content as well as the temperature range in which crystallization takes place. For the alloy containing higher oxygen and crystallized at higher temperature, oxygen-induced metastable f.c.c.-Zr₂Ni precipitates as primary phase. However, for the alloy with lower oxygen content, or with higher oxygen content but crystallized at lower temperature, stable b.c.t.-Zr₂Cu forms as initial precipitation phase. Oxygen retards the precipitation of b.c.t.-Zr₂Cu phase and stabilizes glassy matrix, enhanced thermal stability in the temperature range near glass transition is possessed by the alloy with higher oxygen.