This process was based upon the non-equilibrium thermodynamics of deformable solids. In the case of an ideal solution, the chemical potential of the diffusing component could be expressed by:

where  was the molar volume, ij was the stress tensor, f was the molar Helmholtz free energy, ij was the Kronecker delta, and ij represented the strain tensor of the crystal lattice. The superscript, a, denoted partial molar values for component-a. The driving force for the intracrystalline diffusion of component-a was given approximately by:

-ij/Caij.

I.Shimizu: Philosophical Magazine A, 1997, 75[5], 1221-35