Size-dependent "malleable-to-brittle" transition in a bulk metallic glass

We report a size-dependent malleability in a Zr-based bulk metallic glass (BMG) under both as-cast and annealed states. A "malleable-to-brittle" transition occurred at a critical sample size of 3 mm in diameter, below which the sample yielded with a consistent strength and above which the sample fractured in a brittle manner with decreasing strength. With minimization of the free volume effect by annealing, it was ascertained that this transition was due to the geometrical size effect rather than the free volume effect. The sharp decrease in strength for BMG within the brittle region was explained in terms of flaw sensitivity.