Mechanical behavior of a zirconium-based bulk metallic glass

The mechanical properties of bulk amorphous Zr-Ti-Ni-Cu-Be alloy (Vitreloy™1) were investigated. Three aspects of the mechanical behavior were studied: flow/fracture behavior; fracture resistance; strengthening and embrittlement due to crystallization. It was demonstrated that the Vitreloy™1 behaved as a von Mises material in which the flow behavior was independent of hydrostatic stress. It was also found that the flow behavior obeyed the Mohr-Coulomb criterion in which the flow stress depended strongly on the stress normal to the shear plane. The fatigue crack propagation behavior of Vitreloy™1 was found to be similar to that of polycrystalline metallic alloys. Fracture toughness as determined using fatigue precracked specimens and notched bend specimens showed no loading rate effect over the range tested. The fracture toughness of Vitreloy™1 was strongly dependent on the shear banding nature at a stress concentrator. Notch root radius and terminal precrack ΔK (i.e., fatigue fracture morphology) was found to significantly affect the shear banding nature. The introduction of nanocrystalline phase(s) via annealing treatment, at a temperature just below the supercooled liquid region, significantly affected the mechanical responses of Vitreloy™1. The flow strength obtained from compression test and Vickers microhardness increased almost linearly with increasing crystalline fraction while the notched toughness decreased with increasing crystalline fraction.