Analysis of coupled diffusion and stress of nanowire using diffusion equation with a chemo-mechanical potential

Abstract

Nanowire is a cylindrical object with nano-order diameter. Because of its low number of defects such as dislocations and twins, nanowire has very high strength. However, its relatively large surface volume fraction compared to bulk materials, enhances its corrosion. This problem inhibits its application. Corrosion of nanowire can be treated as a diffusion of impurity atoms into a base material. This phenomenon is modeled by a diffusion equation. When impurity atoms intrude into the base material, volume expansion occurs. The volume expansion induces internal stress. This stress effects on the diffusion. To count this effect into the diffusion equation, we defined chemo-mechanical potential, which includes internal stress (mechanical effect) to a chemical stress (mechanical effect). A very large volume expansion may causes yielding. Because the stress and the diffusion are coupled, the yielding causes a non-contiguous effect on the diffusion. So we considered the effect of yielding. And we also considered blocking effect, decrease of apparent diffusion coefficient induced by high impurity concentration. We modeled hydrogen diffusion in nickel nanowire counting these effects. We numerically solved the diffusion equation. The obtained results tell that yielding delays the diffusion and it suggests the possibility of diffusion control by external stress.