Composition and size dependent torsion fracture of metallic glasses

Abstract

The fracture of metallic glasses (MGs) of different compositions and sizes down to micrometers under torsion loading were systematically investigated. Contrary to the flat shear fracture along the circumferential plane as commonly supposed under torsion, we find that the torsion fracture of metallic glasses can deviate from flat shear plane, and the fracture angle is closely dependent on the composition and the size of MG samples. With a conversion method, we show that the torsion fracture of both millimeter- and micrometer-sized MGs can be described by the ellipse fracture criterion as originally proposed for the tension fracture. The deviation from the circumferential shear plane under torsion is further shown to intrinsically relate to the fracture toughness of MGs. The tougher MG tends to have a smaller fracture angle with respect to the maximum shear plane, and vice versa, indicating a correlation between the fracture toughness and pressure/normal stress sensitivity in MGs. Our results provide new insights on the fracture mechanism and are helpful to design and control the deformation and fracture behavior of MGs under torsion loading.