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.

系统地研究了不同组成和尺寸的金属玻璃（MGs）在扭转载荷下的断裂，其断裂程度可达到微米。与通常在扭转作用下沿周向平面的平面剪切断裂相反，我们发现金属玻璃的扭转断裂可偏离平面剪切平面，且断裂角度与MG样品的成分和尺寸密切相关。通过转换方法，我们表明，毫米级和微米级MG的扭转断裂都可以用椭圆断裂准则来描述，而椭圆断裂准则最初是为张力断裂提出的。进一步显示，在扭转下与周向剪切平面的偏差本质上与MG的断裂韧性有关。反之亦然，表明MG的断裂韧性与压力/法向应力敏感性之间存在相关性。我们的结果为断裂机理提供了新的见识，并有助于设计和控制在扭转载荷下MG的变形和断裂行为。