Compositional Effects on Structure, Dynamics, Thermodynamic and Mechanical Properties of Zr-Cu-Al alloys

Abstract

Zr-Cu-Al alloys belong to a commercially important family of CuZr-based alloys that form bulk metallic glasses on microalloying of Al. However, the identification of compositions with good glass-forming ability and desirable properties from a vast compositional space remains a major challenge due to complex compositional effects on the structure, dynamics and properties. In the present work, we report molecular dynamic investigations of structure, dynamics, thermodynamic and mechanical properties of Zr$_{50}$Cu$_{50-x}$Al$_x$ and Cu$_{50}$Zr$_{50-x}$Al$_x$ alloys ($x=5,10,15,20,25,30,40$) covering a wide compositional space. Our results and findings lead to some important conclusions that could serve as overarching guidelines for choosing good glass-forming alloy compositions that give Zr-Cu-Al glasses with tailored thermal and mechanical properties. Overall, present results suggest that a good glass-forming Zr-Cu-Al alloy composition leading to an MG with good thermal and mechanical properties should be Cu-rich with Zr concentration in the window 30\%-35\% and Al\% > 20. Our results also highlight the impact of icosahedral short- and medium-range ordering on the dynamics and mechanical properties of the alloys. It is observed that the fractions of the full icosahedra $\langle 0,0,12,0 \rangle$ and the degree of their interconnectivity are directly correlated to the structural relaxation, diffusion, dynamic heterogeneity and mechanical properties.