Modeling precipitation kinetics for multi-phase and multi-component systems using particle size distributions via a moving grid technique

Abstract

The collection and coupling of thermodynamic data following the Calphad framework is important for the computational alloy and process design. The microstructure and the precipitation kinetics have a significant influence on the microstructure and mechanical properties of multi-component alloys in solid state; therefore, it is essential to account for solid state phase transformations via thermo-chemical process simulations. In this work an efficient numerical scheme for a Kampmann-Wagner numerical (KWN) model, which takes into account multi-component nucleation and growth theories via the coupling to the open thermodynamic software-package OpenCalphad, is developed and implemented. By the usage of the Calphad approach, it becomes feasible to describe complex multi-component alloy systems. The developed KWN model can take into account effects resulting from the generation or annihilation of vacancies by an off-equilibrium diffusion constant. For the solution of the particle size distribution an efficient and flexible moving grid algorithm is elaborated, which provides a robust and adaptive solution scheme for the simulation of nucleation, growth, coarsening and reversion. The model is applied to simulate the precipitation kinetics of recently published in-situ anomalous small angle X-ray scattering experiments studying reversion of an AA7xxx alloy and the identified model can reproduce the essential characteristics of these reversion experiments over a wide temperature range.