Yield strength of “brittle” metallic glass

“Brittle” metallic glass (MG) usually fractures catastrophically in a shattering mode under macroscopic compression, because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of such alloys, which brings challenges for studying yield strength. Here we show that the plastic yielding behavior in a brittle Fe-based MG can be successfully activated by decreasing the sample size to micrometer scale to avoid the possible large tensile stress concentrators. The yield strength was found to be at least 33% higher than the fracture strength measured with bulk samples for the present brittle MG. The results further demonstrate that the critical stresses for shear band initiation and propagation are size-independent, while the required stress for cleavage cracking increases with decreasing sample size. The competition of thermodynamic driving forces between the two processes of shear banding and cleavage cracking hence leads to the size-induced brittle-to ductile-transition. These findings clarify the physical nature of the strength of “brittle” MG, implying the great opportunity for using high-strength brittle MGs in devices with small dimensions.