Unique glass formation and mechanical properties of Zr-Cu-based alloys

Abstract

The present thesis investigated systematically the unique glass formation and mechanical behavior of Zr-Cu-based alloys. A new group of glass formation in the vicinity of intermetallics of the phase diagram by rapid quenching was discovered in Zr-Cu binary system. This finding is remarkable considering that in the conventional belief, metallic glass is formed near deep-eutectics through liquid quenching. Surprisingly high Weibull moduli were measured in Zr-Cu-based bulk metallic glasses (BMGs), indicating that these materials are highly uniform in strength, and thus much mechanically reliable. This high strength uniformity of BMGs has made it possible to enhance the plasticity by introducing stress gradient, which can be achieved in modified sample geometries. A "malleable-to-brittle" transition has been observed in Zr-Cu-Al BMG at a critical sample size under both as-cast and annealed states. We clarified that this transition should be attributed to the geometrical size effect rather than the free volume effect.