Thermodynamics of Open Two-Phase Systems with Coherent Interfaces

We develop the thermodynamic theory for the decomposition of a ``coherent'' two-phase open system consisting of an interstitial solid solution in equilibrium with a gas reservoir of solute atoms. It is shown that, contrary to what is expected for incoherent systems, the phase rule is inapplicable and the ``plateau'' on the pressure-composition isotherm does not correspond to two coexisting phases. The coherency strain introduces an...