Influences of Elastic Stress and Interfacial Kinetic Barrier on Phase Evolution Paths of Thin-Film Diffusion Couples

An explicit, finite difference scheme was used to examine the effects of coherency stresses and interface kinetic barriers on the phase evolution of a binary, thin-film diffusion couple. Thin-films, initially consisting of alternating layers of two terminal phases, α and γ, were held at a temperature at which the formation of an intermediate phase, β, at α/γ interface was thermodynamically probable. When either the coherency stresses or interface kinetic barriers are present, the interfacial compositions become time-dependent and, thus, the formation of the thermodynamically stable β phase can be kinetically prohibited at the early stage of the evolution. Even if the initial α/γ thin-films have the same overall composition, the coherency constraint can result in different final equilibrium states depending on either the initial compositions of the α and γ phases or the relative magnitudes of the interfacial kinetic barriers. When both the coherency constraint and interfacial kinetic barriers are present, an intermediate phase can repeatedly form and disappear during the evolution.

MATHEMATICAL MODELLING DRIVEN BY TWO INDUSTRIAL APPLICATIONS: A MOVING‐BOUNDARY APPROACH

This note emphasizes the application of the moving‐boundary methodology in the modelling of two processes of particular industrial relevance. The first model explains the application of the Stefan and Signorini type boundary conditions in the modelling of the thermal cutting of metals by a plasma beam, while the second model shows how interface kinetic conditions, employed within the framework of a two‐phase Stefan‐like model, can describe the dynamics of an aggressive reaction front in concrete‐based materials. Our formulations provide a conceptually new approach towards the understanding of the involved physical processes. The connection between the two models is discussed as well. It relies on the presence of non‐equilibrium conditions driving the moving interface.