Level set simulations of dislocation-particle bypass mechanisms

Particle dispersions strengthen metals by acting as barriers to the motion of dislocations. A full analysis of the mechanisms by which dislocations bypass particles has been hindered because of complexities associated with elastic interactions between dislocation segments, their interactions with particle stress field, the flexibility of the dislocation line in three dimensions and the three-dimensional topological changes that occur. We present the results of full three-dimensional dislocation dynamics simulations, based on the level set method, that naturally accounts for all of these issues. We examine bypass mechanisms for penetrable, misfitting particles and impenetrable particles, with and without a misfit. The simulations show a wide range of bypass mechanisms, including particle cutting, dislocation loop formation and combinations of these. Loops are observed to form in front of and behind particles, on the sides of particles, in between particles, around particles and as combinations of these. Some of the bypass mechanisms are classical and others have never been reported previously. We also observe a novel dislocation multiplication mechanism associated with misfitting particles. The observations are compared with those in the literature and from previous theories and simulations.