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 controlled the resultant defect structure which formed during displacement cascades. Initially self-interstitial atoms sensed the grain boundary region as being a defect collector plate; a 2-dimensional indistinguishable region under tension to which they were attracted. The self-interstitial atoms approached the so-called defect collector plate and, at a certain distance, were able to distinguish the local variations in pressure which were specific to the particular grain boundary misorientation. They then changed their direction in response to the local pressure environment. Thus, even large self-interstitial atom clusters underwent a change in direction in order 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)