Cellular Automaton Modeling of Diffusion, Mixed and Interface Controlled Phase Transformation

A cellular automaton (CA) model coupled with Svoboda’s analytic solution of diffusional phase transformation was established to simulate β-α transition in titanium alloy. A numeric definition of diffusion, mixed and interface mode transformation is put forward and simulated by the newly developed CA model. To the best of our knowledge, this is the first model that is capable of quantifying the effect of interface moving (interface mobility coefficient or transformation driving force factor) and solute diffusion process (diffusion coefficient) on phase transformation types. A critical interface mobility coefficient exists for mixed mode transformation, below and above which interface mode and diffusion mode dominate, respectively. This indicated that, in isothermal diffusion/mixed/interface mode phase transformations, solute diffusion distance and solute concentration gradient are decreasing gradually with time. Furthermore, it was found during cooling transformation that diffusion mode transformation at high temperature shifts to interface mode at low temperature, where a high cooling rate corresponds to a high transition temperature.