Interfacial equilibrium during a first-order phase transformation in solids

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Abstract
A continuum thermodynamic treatment of the local equilibrium concentration at a two-phase interface during a first-order diffusional phase transition in crystalline solids is presented. It is assumed that the second-phase domain has a spherical morphology, is coherent with the matrix, and possesses different elastic constants than the matrix. It is shown that the equilibrium concentration at the solid–solid interface is strongly coupled to the stress states of the matrix, precipitate, and interface as well as the interfacial curvature. This coupling gives rise to many new phenomena, such as the dependence of the equilibrium interfacial concentrations on the magnitude of the supersaturation in the parent phase, the misfit between the precipitate and matrix and the difference in the partial molar volumes of the diffusing species. Capillarity is also strongly influenced by the crystallinity through the surface stress and deformation, supersaturation of the parent phase, and the degree of elastic inhomogeneity. It is concluded that approximating the equilibrium interfacial conditions during phase transformations in solids using thermodynamics which is valid only for fluids may be erroneous in many cases.

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