A new model for diffusional growth with Nonequilibrium Interface Conditions

Abstract

A new model for diffusional growth including massive transformations is presented. The thermodynamic stability of a thin layer at the interface determines if a transformation can occur. A new mass balance relation for the phase transformations at the interface is introduced. The interface velocity is modeled as a function of the interphase structure and of the Gibbs molar free energy difference for the transformation of the layer. The interface compositions are de-termined by the dynamics of the system,i.e., no assumption about the interface composition,e.g., local equilibrium, is made. No special treatment is necessary to cover,e.g., para-equilibrium, as it is automatically included by the general formalism. Transinterphase diffusion is includedvia a simple description. The model can simulate both diffusion control and interface control. The model is demonstrated for a simple model system and the austenite-to-ferrite trans-formation in an Fe-0.11 pct C alloy at 770 °C.