Intergranual void motion in un-passivated lines with Void-Grain Boundary Interaction
Figure 1: Snap shuts from the void grain boundary interaction are presented, where only the capillary forces are taken into account. This figure shows that the void and grain boundary combine system starts to evolve towards the equilibrium configuration having proper dihedral angles dictated by thermostatic theory, as soon as they have in close contact with each others.
The rate of this evolution process is controlled by three seemingly independent unit processes, namely: the mobility of surface drift-diffusion, and the generalized mobilities associated with longitudinal movement of triple junction and the transverse flow of matter through the junction, respectively. The first one corresponds to the long range material transport, and the other two are closely related to in situ transfer reactions (highly localized fashion) taking place at the triple junction. Since our computer simulation operates in the normalized and scaled time and space domain, in the absence of growth phenomenon, one deals with only two normalized mobilities which are designated as longitudinal and transverse triple junction generalized mobilities. In the present experiments, we assumed that both normalized mobilities are unity.
Figure 2: The void intergranual motion and the shape evolution under the action of capillary and electromigration forces are presented as a series of snap shuts. This figure shows very interesting dynamical behavior of a void, namely; the penetration through, and then detachment from the grain boundary with simultaneous formation of a daughter void at advancing front. One observes the effect of capillary forces more clearly when the sharp (slit-like) tail of the void starts to round up immediate after the detachment (detrapping) stage is completed. At the final phase of this computer experiments, one sees the penetration of the daughter void into the neighboring grain boundary while the parent void trailing behind. As far as the triple junction behavior under the action of external forces is concerned, one may observe that it is highly dynamical in character, showing large and time dependent departure from the equilibrium configuration just contrary to the general presumptions in many theoretical treatments in the literature.