Tensile and fatigue fracture mechanisms of a Zr-based bulk metallic glass

The tensile and fatigue fracture behavior of Zr59Cu20Al10Ni8Ti3 bulk metallic glass was investigated. It was found that under tensile load the metallic glass always displays brittle shear fracture and the shear fracture plane makes an angle of θT (=54°) with respect to the stress axis, which obviously deviates from the maximum shear stress plane (45°). Under cyclic tension-tension loading, fatigue cracks first initiate along the localized shear bands on the specimen surface, then propagate along a plane basically perpendicular to the stress axis. Tensile fracture surface observations reveal that fracture first originates from some cores, then propagates in a radiate mode, leading to the formation of a veinlike structure and final failure. The fatigue fracture processes of the specimens undergo a propagation stage of fatigue cracks followed by catastrophic failure. Based on these results, a tensile fracture criterion for bulk metallic glasses is proposed by taking the effect of normal stress into account. It is suggested that both normal and shear stresses affect the fracture process of metallic glasses and cause the deviation of the fracture angle away from 45°