Unified upper temperature for cryogenic thermal cycling treatment in Fe-based bulk metallic glasses

Fe-based bulk metallic glasses have high fracture strength and large elastic limit. However, the extremely poor plasticity at room temperature severely renders their wide use as structural materials. In this work, three Fe-based bulk metallic glasses were selected to explore the effect of the upper temperature for cryogenic thermal cycling treatment on the plasticity of the specimens after rejuvenation. It was found that all three Fe-based bulk metallic glasses exhibit the largest plasticity when the upper temperature is about 0.62Tg, where Tg is glass transition temperature. The underlying mechanism is understood by the evolution of the structural heterogeneity dominates by the competition between structural rejuvenation and physical aging during the CTC treatment. When the upper temperature is relatively low, the structural rejuvenation dominates, which causes an increase of the plasticity of bulk metallic glasses; Otherwise, a too high upper temperature leads to a physical aging, resulting in the decline of plasticity. This work will provide process reference for the cryogenic thermal cycling treatment of Fe-based bulk metallic glasses.