A Ni-free Zr-based bulk metallic glass with remarkable plasticity

Abstract

The effect of Nb and Pd combination on the glass forming ability (GFA) and mechanical properties of Zr 53Cu 30Nb x Pd 9 −x Al 8 ( x = 3.5–6.0) bulk metallic glasses (BMGs) were systematically investigated by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and compression test. TEM observation revealed that a nanocrystalline phase embeds in the amorphous matrix of the as-cast Zr 53Cu 30Nb 4.5Pd 4.5Al 8 alloy. A tiny nano-crystalline phase (with size about 5–20 nm) embedded uniformly in the amorphous matrix of the Zr 53Cu 30Nb 4.5Pd 4.5Al 8 alloy was observed and identified to be the tetragonal structured NbPd 3 phase based on the analyses of nano beam electron diffraction. According to the results of thermal analyses, the composition of Zr 53Cu 30Nb 5Pd 4Al 8 and Zr 53Cu 30Nb 4.5Pd 4.5Al 8 present the optimum GFA as well as thermal stability in the Zr 53Cu 30Nb x Pd 9 −x Al 8 ( x = 3.5–6.0) alloy system. In addition, the result of compression test shows that the yield strength significantly increases from 1700 MPa (Zr 53Cu 30Nb 5Pd 4Al 8) to 1900 MPa (Zr 53Cu 30Nb 4.5Pd 4.5Al 8). A remarkable compression plastic strain (11.2%) occurs at Zr 53Cu 30Nb 4.5Pd 4.5Al 8 BMG rod with 2 mm in diameter. This significant increase in plasticity is presumably due to the restriction on shear banding by the nano-size second phase.