Failure mechanisms of metallic glasses via atomic scale simulations

Abstract

Metallic glasses (MGs) are an emerging class of structural materials that can achieve a combination of striking mechanical properties, such as high strength, large elastic limit, high fracture toughness, plastic-like processability, etc. However, the wide application of MGs in daily life is largely hindered by their extreme tensile brittleness and the uncertainty in their fatigue behavior. The underlying failure mechanisms are experimentally intractable due to spatiotemporal limitations.

Here, we designed several novel atomic simulation methods to reveal atomic insights on the tensile and fatigue failure mechanisms. Under tension, we found that the failure of MGs is triggered by cavitation and that the fast shear flow can decrease MGs' resistance to cavitation by a surprisingly large amount, which explains the extreme tensile brittleness. Under cyclic loading, we found that the life of MG nanowires follows the Coffin-Manson relationship, which can be further derived from the plastic strain controlled microscopic damage accumulation. By force field tuning methods, we demonstrated that the propensity of both the tensile brittleness and the fatigue failure of MGs is correlated with Poisson's ratio and the degree of covalency in the bonding. The atomic insights discovered here shed light on how to improve the tensile ductility and reliability of MGs, via tuning the elastic properties, thermal properties and sample size.