Comprehensive unified model and simulation approach for microstructure evolution

The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials. There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches. This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution, emphasizing their advantages and disadvantages. Atomistic approaches, such as molecular dynamics, are restricted by the scale of the studied system because they are computationally expensive. Continuum mesoscale simulation approaches, such as phase field, cellular automata, and Monte Carlo, have inconsistent phenomenological equations, each of which only describes one aspect of microstructure evolution. To provide comprehensive insight into microstructure evolution, a unified model that is capable of equally evaluating the nucleation and growth processes is required. In this paper, a physics-based model is proposed that incorporates statistical mechanics, the energy conservation law, and the force equilibrium concept to include all aspects of microstructure evolution. A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments. Furthermore, the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed. The use of fundamental physical rules instead of phenomenological equations, together with the real spatial and temporal scales of the proposed model, facilitates the comparison of the simulation results with experimental results. To examine the accuracy of the proposed simulation approach, the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.