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

The effect of Nb and Pd combination on the glass forming ability (GFA) and mechanical properties of Zr53Cu30NbxPd9−xAl8 (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 Zr53Cu30Nb4.5Pd4.5Al8 alloy. A tiny nano-crystalline phase (with size about 5–20 nm) embedded uniformly in the amorphous matrix of the Zr53Cu30Nb4.5Pd4.5Al8 alloy was observed and identified to be the tetragonal structured NbPd3 phase based on the analyses of nano beam electron diffraction. According to the results of thermal analyses, the composition of Zr53Cu30Nb5Pd4Al8 and Zr53Cu30Nb4.5Pd4.5Al8 present the optimum GFA as well as thermal stability in the Zr53Cu30NbxPd9−xAl8 (x = 3.5–6.0) alloy system. In addition, the result of compression test shows that the yield strength significantly increases from 1700 MPa (Zr53Cu30Nb5Pd4Al8) to 1900 MPa (Zr53Cu30Nb4.5Pd4.5Al8). A remarkable compression plastic strain (11.2%) occurs at Zr53Cu30Nb4.5Pd4.5Al8 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.

Research highlights
► Based on the results of thermal analyses, we found that Zr53Cu30Nb5Pd4Al8 and Zr53Cu30Nb4.5Pd4.5Al8 alloys present the optimum GFA as well as thermal stability in the Zr53Cu30NbxPd9−xAl8 (x = 3.5∼6.0) alloy system.
► A tiny nanocrystalline phase (with size about 5–20 nm) embedded uniformly in the amorphous matrix of the Zr53Cu30Nb4.5Pd4.5Al8 alloy was observed and identified to be the tetragonal structured NbPd3 phase.
► A remarkable compression plastic strain (11.2%) with 1900 MPa yield strength occurs at Zr53Cu30Nb4.5Pd4.5Al8 BMG rod.
► This significant increase in plasticity is presumably due to the restriction on shear banding by the nano-sized second phase.