Correlations between the relaxed excess free volume and the plasticity in Zr-based bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) with Nb minor alloying have been fabricated with different free volume (FV) trapped in. FV is evaluated by the relaxed excess free volume (REFV) after annealing just below Tg through loop thermal expansion tests. The results show that there is a qualitative correlation between the plasticity and REFV in Zr-based BMGs. The larger amount of excess FV the BMGs relax, the better plasticity they exhibit. With 1.5% Nb addition, the brittle Zr65Cu15Ni10Al10 BMGs possess REFV up to about 0.428% and exhibit the relatively good plasticity up to 25.6%. This provides a promising way to estimate the plasticity of BMGs and design new ductile BMGs through the minor alloying.