How the random diffusive displacement of voids in a solid depends on the void size

What is it about?

We investigated how tiny (nano) voids randomly move around in a solid using computer simulations. The motion takes place by displacement of single atoms of the material around the void. The void speed depends on their size. As a function of size, the speed at first increases, then it reaches the fastest point, and after that, it slows down. This is unusual because usually, large clusters move slower than small ones. We explain that this happens because the shape of the void affects how fast it can move. We created a model that explains this. Furthermore, at low temperatures and small sizes, we noticed that some special-size voids displace slower than expected from the general behavior. This happens because, for specific void shapes, the surface atoms are tightly held and thus move less. Therefore, the motion of the whole void is slowed down.

Featured Image

Photo by Valentin Lacoste on Unsplash

Photo by Valentin Lacoste on Unsplash

Why is it important?

The random diffusive motion of voids in a solid significantly influences material properties, because they can coalesce and grow, and can ultimately lead to material failure. In this study, we have investigated the diffusion of nanovoids using kinetic Monte Carlo simulations. One of the key findings of our investigation is the discovery of a non-conventional trend in the diffusion coefficient as a function of void size. It is widely accepted that the diffusion of clusters decreases as their size increases. However, our research uncovers an initial increase in diffusion as the void size grows, followed by a flattening and then a decrease. The main advances of our work are three: (i) The diffusion coefficient, as a function of the size of 3D nanovoids, grows, reaches a maximum, and then decreases. (ii) To account for void curvature effects, we have developed an analytical expression that successfully reproduces the observed trend described above (iii) Some special clusters, which exhibit a compact shape, diffuse more slowly than the general trend

Perspectives