Dislocation nucleation and vacancy formation during high-speed deformationof fcc metals

Recently, a dislocation-free deformation mechanism was proposed by Kiritani et al. on the basis of a series of experiments where thin foils of fee met als were deformed at very high strain rates. In the experimental study, the y observed a large density of stacking fault tetrahedra but very low disloc ation densities in the foils after deformation. This was interpreted as evi dence for a new dislocation-free deformation mechanism, resulting in a very high vacancy production rate. In this paper we investigate this propositio n using large-scale computer simulations of bulk and thin films of copper. To favour such a dislocation-free deformation mechanism, we have made dislo cation nucleation very difficult by not introducing any potential dislocati on sources in the initial configuration. Nevertheless, we observe the nucle ation of dislocation loops, and the deformation is carried by dislocations. The dislocations are nucleated as single Shockley partials. The large stre sses required before dislocations are nucleated result in a very high dislo cation density, and therefore in many inelastic interactions between the di slocations. These interactions create vacancies and a very large vacancy co ncentration is quickly reached.