Difference in compressive and tensile fracture mechanisms of Zr59CU20Al10Ni8Ti3 bulk metallic glass

The compressive and tensile deformation, as well as the fracture behavior of a Zr59Cu20Al10Ni8Ti3 bulk metallic glass were investigated. It was found that under compressive loading, the metallic glass displays some plasticity before fracture. The fracture is mainly localized on one major shear band and the compressive fracture angle, theta(C), between the stress axis and the fracture plane is 43degrees. Under tensile loading, the material always displays brittle fracture without yielding. The tensile fracture stress, sigma(F)(T), is about 1.58 GPa, which is lower than the compressive fracture stress, sigma(F)(C)( = 1.69 GPa). The tensile fracture angle, sigma(F)(T), between the stress axis and the fracture plane is equal to 54degrees. Therefore, both theta(C) and theta(T) deviate from the maximum shear stress plane (45degrees), indicating that the fracture behavior of the metallic glass under compressive and tensile load does not follow the von Mises criterion. Scanning electron microscope observations reveal that the compressive fracture surfaces of the metallic glass mainly consist of a vein-like structure. A combined feature of veins and some radiate cores was observed on the tensile fracture surfaces. Based on these results, the fracture mechanisms of metallic glass are discussed by taking the effect of normal stress on the fracture process into account. It is proposed that tensile fracture first originates from the radiate cores induced by the normal stress, then propagates mainly driven by shear stress, leading to the formation of the combined fracture feature. In contrast, the compressive fracture of metallic glass is mainly controlled by the shear stress. It is suggested that the deviation of theta(C) and theta(T) from 45degrees can be attributed to a combined effect of the normal and shear stresses on the fracture plane. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.