Low temperature plasticity maximum in a Zr-Cu-Ni-Al bulk metallic glass

Abstract

The structural and mechanical properties of Zr₆₀Cu₂₀Ni₁₀Al₁₀ bulk metallic glass (BMG) were investigated using thermal and mechanical tests conducted over a wide temperature range from 5 K to 536 K. We reveal that the Zr-Cu-Ni-Al BMG exhibits significantly improved flexural strength and plasticity when bent at 77 K, in contrast to its behavior at room temperature. This behavior differs from other BMG systems, such as Zr-Cu-Ag-Al, Ti-Zr-Ni-Be-Cu, and La-Al-Ni-Cu-Co, which typically become more brittle as the temperature decreases. At 77 K, the high bending plasticity is attributed to the formation of numerous shear bands with lower average spacing, which play a vital role in accommodating plastic deformation. The fracture surface analysis reveals wide shear offsets and distinct steady-state growth regions, indicating enhanced plasticity at this temperature. Further investigations into the fundamental mechanisms indicate that the temperature-dependent plasticity difference between Zr-Cu-Ni-Al and Zr-Cu-Ag-Al BMGs is mainly associated with atomic arrangement efficiency and free volume dynamics, while the influence of phase separation on high plasticity is relatively minor. These findings highlight the significant role of atomic packing efficiency and free volume in promoting the formation of multiple shear bands and ultimately improving the mechanical performance of BMGs.