The microstructure of a multiphase coating evolves during service.
Processes include oxidation, phase transformation, evaporation, diffusion
and deformation. We first consider an internal region of a single phase,
away from boundaries of various kinds. Diffusion induces a dilatation
field, which is incompatible, driving the alloy to deform plastically. Since
Darkenšs one-dimensional theory has been used widely to interpret diffusion
experiments, it is desirable to extend his theory into a three dimensional
theory with minimum tinkering. Following Darken, we neglect elastic strain,
compositional strain, and vacancy concentration change. The governing
equations, formulated in the Eulerian space, simultaneously evolve
concentration field and creep velocity field. We then examine the
conditions at phase boundaries, oxide-metal interfaces, and vapor-metal
interfaces. We apply the theory to analyze several cases.
This work is done in collaboration with D. Kubair, D.R. Clarke, V. Tolpygo, A.G. Evans, and G. Meier.