Atomistic scale fracture behaviours in hierarchically nanotwinned metals

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.

Keywords:

• molecular dynamics simulations
• fracture
• crack growth
• twins
• hierarchically nanotwinned structures

Acknowledgements

The authors would like to acknowledge the financial support of the National Key Basic Research Program of China (Grants No. 2012CB932203 and No. 2012CB937500) and NSFC (Grants No. 11002151, No. 11222224, No. 11072243 and No. 11021262). The simulations reported were performed at Supercomputing Center of Chinese Academy of Sciences.