Effects of Nb Addition on Glass-Forming Ability, Thermal Stability and Mechanical Properties of Ti-Based Bulk Metallic Glasses

Ti-based bulk metallic glasses (BMGs) alloy of (Ti40Zr25Cu9Ni8Be18)100-xNbx with x=0, 1, 3, 4 and 5 at% were prepared by copper mould casting. Cylindrical rods of more than 6 mm in diameter consisting of fully glassy single phase were obtained. The effects of Nb addition on the glass-forming ability (GFA) and thermal stability of the (Ti40Zr25Cu9Ni8Be18)100-xNbx alloy were studied by X-ray diffraction (XRD), transmission electron microscope (TEM) and differential scanning calorimeter (DSC). Mechanical properties were measured on a MTS810-type machine at room temperature under a compressive mode with a strain rate of 2 × 10−4 s−1. It is found that the GFA is not influenced and the thermal stability is increased by Nb addition. With the increase of Nb content, the alloys exhibit high fracture strength. When Nb content x=4, the (Ti40Zr25Cu9Ni8Be18)96Nb4 rod of fully glassy single phase exhibits the highest compressive strength of 1945 MPa and plastic elongation of about 7.0%, showing significant plasticity improvement. The large ductility of (Ti40Zr25Cu9Ni8Be18)96Nb4 is due to the development of the large density shear bands proved by scanning electron micrographs (SEM).