An application of irreversible thermodynamics to diffusional phase transformations

The method of transforming the set of flux equations for two simultaneous processes into a new set of processes is reviewed and applied to diffusion in one-phase materials where the two primary equations describe the individual diffusion of the components and the new ones describe the migration of Kirkendall markers and interdiffusion. It is then modified to apply to a two-phase material with a diffusional transformation and the new equations then describe the migration of the phase interface and interdiffusion across the interface. Comparison is made with previous attempts. In order to treat the transition from diffusion-controlled to partitionless growth it may be necessary to introduce a third primary flux equation. It is possible to incorporate this third flux within the other two, in which case it will contribute substantially to their cross-coefficients.