Enhancement of glass forming ability and plasticity by addition of Nb in Cu–Ti–Zr–Ni–Si bulk metallic glasses

The effect of Nb substitution for Zr on the glass forming ability (GFA) and mechanical properties of Cu47Ti33Zr11−xNbxNi8Si1 (x = 0, 2, 4, 6, 8, 11) alloys have been investigated using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), high resolution transmission electron microscope (HRTEM), and atom probe field ion microscope (APFIM). Partial substitution of Zr by Nb in Cu47Ti33Zr11Ni8Si1 promotes the GFA. Cu47Ti33Zr11−xNbxNi8Si1 (x = 2, 4) bulk metallic glasses (BMGs) with diameter of 5 mm can be fabricated by Cu-mold injection casting method. The plastic elongation of ∼4.2% in Cu47Ti33Zr7Nb4Ni8Si1 BMG, when compared with ∼1.5% in Cu47Ti33Zr11Ni8Si1 BMG, demonstrates that small amount of Nb addition can have a dramatic effect on plasticity enhancement in Cu–Ti–Zr–Ni–Si BMG. HRTEM and APFIM results show that the as-cast Cu47Ti33Zr7Nb4Ni8Si1 BMG exhibits a fully amorphous structure without nm-scale compositional fluctuation, indicating that the plasticity of the BMGs can be improved even though no microstructural obstacles hindering or branching the propagation of the shear bands are observed by HRTEM and APFIM.