Glass forming ability and mechanical properties in Ti-Cu-based bulk metallic glasses

Abstract:

In this paper, the composition of the Ti-Cu-Ni-Zr bulk metallic glasses(BMGs) was designed based on “binary eutectic mixture” method. The Ti-Cu-Ni-Zr alloy rods were prepared with the different diameters by a method of water-cooled copper mold casting. The thermodynamic parameters were tested and the microstructure were investigated by differential scanning calorimeter(DSC), X-ray diffraction(XRD), universal testing machine and scanning electron microscope(SEM). The experimental results show that the Ti-Cu-Ni-Zr BMGs have the high glass forming ability, and the critical diameter can reach 4 mm. The glass forming ability of Ti-Cu-Ni-Zr BMGs are approximately equal, and charactering the thermodynamic parameters of glass formation ability, such as supercooled liquid region DTx, g parameter, reduced glass transition temperature Trg, are also approximately equal, respectively. Based on the disscussion of mechanical properties, the results show that the Ti_32.3Cu_47.6Ni_7.9Zr_12.2 and Ti_31.6Cu_48.2Ni_7.7Zr_12.5 BMGs have the plastic of 0.7% and 0.2%; however, the fracture mechanism of Ti₃₀Cu_49.5Ni_7.2Zr_13.3 and Ti_28.55Cu_50.7Ni_6.75Zr₁₄ BMGs are the similar brittle fracture. For the Ti-Cu-Ni-Zr BMGs, the greater the plastic deformation is, the more the number of the shear bands are, the greater the depth are, and vice versa. In addition, for the plastic materials, when the amplitude of the serrated flow is the larger, the depth of the surface shear bands is more larger; and vice versa. For the approximate brittle materials, the serrated flow corresponds to the initiation of the second shear band; and for the completely brittle materials, the phenomenon of serrated flow is not found in the stress-strain curves, however, the shear bands were not found on the surface of the sample.