Atomistic simulations of diffusive phase transformations with non-conservative point defects

Most of the phase transformations modifying the microstructure, thereby the materials properties, are controlled by the diffusion of atoms. The rate but also the selection of phase transformations depend on the concentration of lattice point defects (PDs), because substitutional atoms exchange with PDs to diffuse and PDs are non-conservative species. During manufacturing or in use, whenever PD diffusion and creation/annihilation reactions at extended defects in the microstructure are slower than the kinetics of the microstructure, these PDs may not have their equilibrium concentration. A departure of PDs from local equilibrium can be transient under thermal conditions, or permanent in materials driven out of equilibrium as under irradiation. Non-equilibrium PDs can have a dramatic effect on the evolution of the microstructure or even on the stationary microstructure in driven systems. We present an atomic kinetic Monte Carlo (AKMC) method, which is able to tackle the atomic-scale couplings between PD diffusion, annihilation/creation reactions and the kinetics of decomposition of a solid solution into a two-phase microstructure. By introducing PD source-and-sinks (SAS) at specific lattice sites, we control the PD reactions and highlight the role of non-equilibrium quenched-in point defects on the evolution kinetics of short-range order parameters and subsequent second-phase precipitation. Then, we open the discussion on various kinetic phenomena that require taking into account the role of non-equilibrium PDs at different scales of time and space. (authors)