Flaw-Insensitive Fracture of a Micrometer-Sized Brittle Metallic Glass

Brittle materials, such as oxide glasses, are usually very sensitive to flaws, giving rise to a macroscopic fracture strength that is much lower than that predicted by theory. The same applies to bulk-metallic glasses (BMGs), with the important difference that these glasses can exhibit certain plastic strain prior to the catastrophic failure. Here we consider the strongest metallic alloy known, a ternary Co55Ta10B35 BMG. We show that this macroscopically brittle glass is flaw-insensitive at the micrometer scale. This discovery emerges when the testing pre-cracked specimens with self-similar geometries, where the fracture stress does not decrease with increasing pre-crack size. The fracture toughness of this ultra-strong glassy alloy is further shown to increase with increasing sample size. Both these findings deviate from our classical understanding of fracture mechanics, and are attributed to a transition from toughness-controlled to strength-controlled fracture below a critical sample size.