A model of discontinuous precipitation based on the balance and maximum production of the entropy

Abstract

A model of discontinuous precipitation in supercooled binary polycrystalline alloys at reduced temperatures, taking place as a result of the diffusion-induced grain boundary migration, is constructed with allowance of grain boundary diffusion. The proposed approach allows independent determination of the main parameters, including the interlamellar distance, the maximum velocity of the phase transformation front, and the concentration jump at this boundary. This is achieved by using a set of equations for the (i) mass transfer in the moving interphase boundary, (ii) balance of the entropy fluxes at the phase transformation front, and (iii) maximum rate of the free energy release. The model uses a minimum of thermodynamic information on the two-phase system: the curvature of the Gibbs potential surface in the decomposing phase and the free energy of the interface between the new phases. Theoretical results are compared to the available experimental data.