Emergence of enhanced strengths and Bauschinger effect in conformally passivated copper nanopillars as revealed by dislocation dynamics
Seok-Woo Lee (CalTech), Andrew Jennings (California institute of Technology), Julia Greer (Caltech)
Discrete Dislocation Plasticity
Tue 4:20 - 5:40
RI Hall 108
The ability to precisely control the surface state of a nanostructure may offer a pathway towards tuning the mechanical properties of small-scale metallic components. In our experimental work, single crystalline Cu nanopillars were conformally coated with a 5-25 nm-thick layer of TiO2/Al2O3. Uniaxial compression tests revealed two key findings associated with these passivated samples: (1) ~80 % higher strengths as compared with the uncoated samples of the same diameter, 200 nm, and (2) Bauschinger effect-like hysteresis during unloading-reloading segments. Dislocation dynamics simulations of uniaxially compressed 200 nm-diameter Cu nanopillars with coated surfaces revealed the contribution of dislocation multiplication, pinning, and pile-up processes to the experimentally observed enhancement in pillar strength. They further helped explain the transition of plasticity mechanisms from dislocation multiplication via the operation of single-arm dislocation sources to dislocation nucleation from the crystal-coating interface. Hysteresis in stress-strain data is discussed in the framework of dislocation structure evolution during unloading-reloading cycles in experiments and simulations.