Simulations of nanocrystalline materials revealed that the pressure gradient within the structure could play a key role in the movement of self-interstitial atoms to surrounding grain boundaries, and therefore in the resultant defect structure which formed in displacement cascades. The initially self-interstitial atoms sensed the grain-boundary region as being a so-called defect collector plate. That is, a 2-dimensional indistinguishable tension region to which they were attracted. The self-interstitial atoms approached the collector plate and, at a certain distance, were able to distinguish the local variations in pressure which were specific to a particular grain boundary misorientation. This changed their direction in response to the local pressure environment. Thus, even large self-interstitial clusters underwent a change in direction; moving so as to reach and follow a lower compressive (and, where possible, a tensile pressure path) to the grain boundary.

Movement of Interstitial Clusters in Stress Gradients of Grain Boundaries. M.Samaras, P.M.Derlet, H.Van Swygenhoven, M.Victoria: Physical Review B, 2003, 68[22], 224111 (6pp)