UC Irvine

A mixture of structural heterogeneity has been a promising way to design materials with excellent mechanical properties. Yet, the significance of how structural heterogeneity tunes the deformability and its associated deformation mechanisms is still not lucid. In this work, we dive into two types of metallic materials, namely nanotwinned metals and monoatomic Ta metallic glass, to address this issue. In nanotwinned metals, we survey a range of nanotwinned materials that possess different stacking fault energies (SFEs), and understand the TB strengthening limit. Distinct from Cu and Al, the nanotwinned, ultralow SEF materials (Co, NiCoCr, and NiCoCrFeMn) intriguingly exhibit a continuous strengthening down to a twin thickness of 0.63 nm. Examining dislocation slip mode and deformation microstructure, we find the hard dislocation modes persist even when reducing the twin boundary spacing to a nanometer regime. Meanwhile, the soft dislocation mode, which causes detwinning in Cu and Al, results in phase transformation and lamellar structure formation in Co, NiCoCr, and NiCoCrFeMn. In monoatomic Ta metallic glass, it is found that deformability is directly associated with inherent structural heterogeneity on the level of atomic order. We find the dispersive and sparse distribution of local order is associated with necking, yet percolation of medium-range order constrains the deformability and results in brittle failure. These findings shed new light on the role of structural heterogeneity in metallic materials, which has important implications for the design of nanoscale metallic materials with tunable mechanical properties.