Size effects on the compressive deformation behaviour of a brittle Fe-based bulk metallic glass

The mechanical behaviour of brittle Fe-based bulk metallic glass (BMG) samples with different diameters and aspect ratios (ARs) has been investigated. For samples with an AR of 2, the fracture strength increases with a decrease in the sample diameter which can be well-explained by the Weibull analysis with a Weibull modulus of 34. For samples with a fixed diameter of 2 mm, a transition between three deformation modes, i.e. fragmentation, distensile cracking and confined shearing was observed as the AR was decreased. When the AR is below 0.19, large friction between the platen and specimen end suppresses the distensile cracking and prompts shear deformation, resulting in multiple shear bands and large compressive plasticity. Our analysis indicates that the deformation mode of brittle BMGs strongly depends on the applied stress conditions and can exhibit ductile characteristics under constraints. The present findings are important for engineering applications of brittle BMGs in which various geometries will be used.