Trapping and Escape of Dislocations in Micro-crystals With External and Internal Barriers (Preprint)

摘要

We perform three-dimensional dislocation dynamics simulations of solid and annular pillars, having both free surface boundary conditions, or strong barriers at the outer and/or inner surfaces. Both pillar geometries are observed to exhibit a size effect where smaller pillars are stronger. The scaling observed is consistent with the weakest-link activation mechanism and depends on the solid pillar diameter, or the annular pillar effective diameter, Deff= D-Di. An external strong interface is observed to dramatically increase the dislocation density by an order of magnitude due to trapping dislocations at the interface. In addition, a considerable increase in the flow strength by up to 60% from simulations having free surface boundary conditions is observed. As the applied load increases, weak spots form on the surface of the pillar by dislocations breaking through the interface when the RSS is greater than the barrier strength. The hardening rate is also observed to increase with increasing interface strength.