Effect of twin spacing on the mechanical behavior and deformation mechanism of nanotwinned Al

The effect of twin spacing on the mechanical behavior and deformation mechanism of nanotwinned Al with high stacking fault energy (SFE) is investigated by molecular dynamics simulation, and the results are compared to nanotwinned Ni and Cu with different SFEs under the same simulation conditions. It is found that the nanotwinned Al with small grain size shows a strengthening-softening transition with the reduction of twin spacing, which is attributed to the transition of dislocation from inclined to twin boundaries (TBs) to parallel to TBs. Such observations are consistent with most nanotwinned metals with low SFE. However, the nanotwinned Al with large grain size shows a continuous strengthening with the decrease of twin spacing. It originates from the strain localization in grain boundaries, which decreases with the reduction of twin spacing, and few dislocations are activated in the tensile processes. The high ratio of stable SFE to unstable SFE in nanotwinned Al inhibits the partial dislocation emission, especially for the nanocrystalline structure with large grain size, which results in the different mechanical behaviors and deformation mechanisms in the nanotwinned Al.