Dislocation climb effects on particle bypass mechanisms

We examine the effects of dislocation climb on the mechanisms by which dislocations bypass particles. The analysis is based upon three-dimensional, level-set, dislocation dynamics simulations that include all elastic interactions, dislocation glide, cross-slip and climb, and particles that are either impenetrable or penetrable and either with or without misfit. When the particle is misfitting with respect to the matrix, the dislocation migration is strongly influenced by the elastic fields created by the misfit. An edge dislocation tends to climb towards either the top or bottom of the particle and may remain there if the stress is not too large. A screw dislocation may wrap around the particle several times, creating a helical dislocation structure at small applied stresses. If the stress is increased, these helices break into an array of loops. Without misfit, climb invariably lowers the threshold stress particle bypass. However, in the misfit case, climb can also lead to more stable dislocation structures and, hence, increases the threshold stress. This report emphasizes the detailed bypass and pinning mechanisms and provides insight into the conditions under which these mechanisms operate.