| Abstract Scope |
Many diffusional processes involve molar volume variations. In solids, the molar volume variation affects diffusion by (1) introducing an enthalpic mechanical driving force for diffusion due to the compositional strains; (2) generating non-zero velocities between the lab and the molar reference frames. To systematically and consistently investigate these effects, we first theoretically derive the diffusion equations under variable molar volume, and use the example of the Ni-Al system to quantify the effect of molar volume variation on diffusion behaviors. We then extend this framework to the phase-field approach, and use the examples of è’ precipitation in Al-Cu alloys to quantify how the molar volume variations affect the precipitation morphology and kinetics. This study will lay the foundation for elucidating the diffusion behaviors under variable molar volume, and more accurately predict the morphology evolution and kinetics of diffusional processes by integrating thermodynamic, diffusion mobility and molar volume databases, and phase-field modeling. |