Modeling Displacive-Diffusional Coupling in Solid State Processes

Abstract

Microstructural evolution in materials often involves coupled displacive and diffusional processes as a rule rather than as an exception. For example, structural phase transformations often involve coupled lattice shear, shuffle, and diffusion. Dislocation shearing of ordered precipitates can couple strongly to chemical reordering. In these processes it is the coupling that governs the rate of transformation and deformation. Mechanistic studies of these mechano-chemically coupled processes require modeling capabilities at atomistic length scales but diffusional time scales. In this presentation, we introduce a new approach, called diffusive molecular dynamics (DMD), which can capture diffusional time scale while maintaining atomic resolution, by coarse-graining over atomic vibrations. DMD combines long-range elastic and short-range atomic coordinate interactions simultaneously with gradient chemical thermodynamics. Kinetically it solves the master equation for diffusion on a moving atom grid. Examples will be given to demonstrate applications of DMD to various solid-state processes that involved coupling between displacive and diffusional atomic movements, including nanoindentation and climb of extended dislocations