Abstract
In the present study, a series of large-scale molecular dynamics simulations have been performed to investigate the atomistic scale fracture behaviours along the boundaries of primary twins in Cu with hierarchically nanotwinned structures (HTS), and compare their fracture behaviours with those in monolithic twins. The results indicate that crack propagation along [1 1 2] on the twin plane in monolithic nanotwins is brittle cleavage and fracture, resulting in low crack resistance and fracture toughness. However, the crack resistance along the boundaries of primary twins in HTS is much higher, and a smaller spacing of secondary twins (λ 2) leads to even higher fracture toughness. With large λ 2, the crack growth is achieved by void nucleation, growth and coalescence. However, considerable plastic deformation and enhanced fracture toughness in HTS could be achieved by the crack blunting and by the extensive dislocation accommodation ahead of the crack tip when λ 2 is small.
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