Modeling of diffusional phase transformation in multi-component systems with stoichiometric phases

In many multi-component systems, phases can be considered stoichiometric. If two phases not stably coexisting are brought into contact, multiple new phases may nucleate at the interface and develop into a sequence of layers with different phase compositions, which grow between the original phases. Inert markers at the original contact may show “splitting” of the marker (Kirkendall) plane, called polyfurcation. Nearly exclusively binary systems have been studied theoretically or experimentally. A thermodynamic model for the kinetics of diffusional phase transformation in multi-component systems and motion of the polyfurcated Kirkendall plane is derived by the thermodynamic extremal principle. The degrees of freedom of the system are discussed rigorously. The model is demonstrated on simulations of kinetics in binary three-phase and ternary four-phase systems.