Modelling grain coarsening in the framework of rational extended thermodynamics

Grain growth and shrinkage at elevated temperatures is a significant phenomenon during the processing of metals. Often, grain coarsening is described without thermodynamic considerations. But since the grain boundary mobility is thermally activated and energy stored in the grain boundaries is released during their motion, a thermodynamic framework is required to capture the various effects of the process. For this purpose, the procedure of Rational Extended Thermodynamics is applied to derive a thermodynamically consistent model for grain coarsening due to the growth and shrinkage of individual grains. Despite the different approach used, a grain growth model is obtained which is similar to existing ones and can be regarded as a thermodynamic extension of that by Hillert (1965) to more general systems. The model reproduces grain growth experiments in pure copper very accurately and predicts the associated energy release. The present approach combining a microstructure description and continuum mechanics can be further used to develop thermomechanical material models considering the microstructure.