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

Abstract

The effect of Nb substitution for Zr on the glass forming ability (GFA) and mechanical properties of Cu 47Ti 33Zr 11− x Nb x Ni 8Si 1 ( 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 Cu 47Ti 33Zr 11Ni 8Si 1 promotes the GFA. Cu 47Ti 33Zr 11− x Nb x Ni 8Si 1 ( 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 Cu 47Ti 33Zr 7Nb 4Ni 8Si 1 BMG, when compared with ∼1.5% in Cu 47Ti 33Zr 11Ni 8Si 1 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 Cu 47Ti 33Zr 7Nb 4Ni 8Si 1 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.