Collapse of stacking fault tetrahedron and dislocation evolution in copper under shock compression

The stacking fault tetrahedron (SFT) is frequently observed in irradiated materials, which distinctly affects the mechanical properties of matrix materials. This work focuses on the collapse of SFT and the following dislocation evolution in single crystal copper under shock compression with molecular dynamics simulations. Our results reveal the collapse pattern of SFT and its dependence on the shock orientations. The SFT undergoes different metastable structures, e.g., a triangular Frank loop, a semi-faulted SFT, and a truncated SFT with two Frank partial dislocations for [111], [11̄0], and [112̄] shock orientation respectively, which provide nucleation sites for dislocation emission. The dependence of dislocation loops and stacking faults formed from SFT on the shock intensity is revealed. As the shock intensity increases, the stress relaxation resulting from the structural transformation of SFT becomes more obvious, and the dislocation density increases more rapidly to a higher peak value. The equilibrium values of von Mises stress and dislocation density after long-time evolution also increase. With the increase of initial temperatures, the critical stress for plastic deformation is found to decrease linearly and the reduction in [112̄] orientation is much smaller than that in [111] and [11̄0] orientations. The dislocation density increases and the stacking faults will decompose into smaller stacking fault pieces to some extent because of thermal fluctuation.