Modeling of two-phase grain structure in the titanium alloy TI-6AL-4V using cellular automata

The static coarsening behavior of the alpha-beta titanium alloy Ti-6Al-4V during heat treatments is modeled using a probabilistic cellular automata model (CA). For this purpose the kinetics of grain growth is described via transformation probabilities which are determined by diffusion mechanisms at grain and phase boundaries. For temperature changes an algorithm is implemented which adjusts the fraction of alpha and beta phase to reach equilibrium phase values. Hence, the CA is capable of calculating grain coarsening as well as grain dissolution in the two-phase area during heating and isothermal treatments at forging temperature. For these calculations, an initial microstructure is used as input and it can be imported from either virtual created microstructures, real micrographs, or electron backscatter diffraction (EBSD) maps. The model output includes mean diameter, grain size distribution, and virtually simulated microstructures which can be easily compared with experimental micrographs. Examples showing a good correlation between the predicted microstructures and experimental results, as well as data from literature, are presented in this work. The successful implementation of this model will lead to predictions of behavior in other dual-phase alloys.