CONTINUUM BASIS FOR DIFFUSION IN REGIONS WITH MULTIPLE DIFFUSIVITY

A continuum model is proposed to consider diffusion situations where distinct types of structural or point defects contribute to the overall diffusivity. With respect to structural defects, the analysis is motivated by diffusion in the presence of a continuous distribution of high-diffusivity paths, such as grain boundaries and dislocations. With respect to point defects, the analysis is motivated by simultaneous diffusion of vacancies and interstitials, or vacancies and substitutionals. As a result of continuum modeling, the analysis is strictly valid in cases where the distribution of defects can be assumed continuous in space-time. The model is illustrated by detailing an example: Dslocation-pipe diffusion under steady-state conditions.