Effect of crystallization on the mechanical properties of Zr_(56.7)Cu_(15.3)Ni_(12.5)Nb_(5.0)Al_(10.0)Y_(0.5) bulk amorphous alloy

摘要

Effects of crystallization behavior on the mechanical properties of Zr_(56.7)Cu_(15.3)Ni_(12.5)Nb_(5.0)Al_(10.0)Y_(0.5) based bulk amorphous alloy (BAA) were studied. Differential scanning calorimetry (DSC) in Ar environment showed three-exothermic peaks at 395, 472 and 659.5 deg C and one-endothermic peak at 852 deg C. Following DSC study, as received BAA samples were heat-treated in vacuum at six different temperatures 300, 450, 600, 700, 800 and 850 deg C. Heat-treated samples were characterized using Vickers microhardness, X-ray diffraction (XRD), differential scanning calorimetry and field emission scanning electron microscopy (FESEM) to study crystallization behavior. It is found that samples heat-treated above the second (472 deg C) and third (659.5 deg C) exothermic peaks show high microhardness values compared to the as processed samples, and brittle cracking along the indent diagonal. As processed samples show clear evidence of shear banding. FESEM examination revealed existence of nano-scale precipitates for samples heat-treated at 600 and 700 deg C, while micro-scale precipitates for 850 deg C samples. Quasi-static compression tests showed compressive strain to failure decrease with heat-treated samples compared to as received ones. Fracture morphology of the compression test samples changes from vein pattern for as received to flat facets with multiple cracks for heat-treated samples. Indentation fracture toughness values decrease almost an order of magnitude for heat-treated samples compared to as received samples.