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 Zr₅₃Cu₃₀Nb_xPd _9-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 Zr₅₃Cu₃₀Nb _4.5Pd_4.5Al₈ alloy. A tiny nano-crystalline phase (with size about 5-20 nm) embedded uniformly in the amorphous matrix of the Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ 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 ₅₃Cu₃₀Nb₅Pd₄Al₈ and Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ present the optimum GFA as well as thermal stability in the Zr ₅₃Cu₃₀Nb_xPd_9-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 (Zr₅₃Cu ₃₀Nb₅Pd₄Al₈) to 1900 MPa (Zr ₅₃Cu₃₀Nb_4.5Pd_4.5Al₈). A remarkable compression plastic strain (11.2%) occurs at Zr₅₃Cu ₃₀Nb_4.5Pd_4.5Al₈ 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.