Phase-field study of ripening and rearrangement of precipitates under chemomechanical coupling
C. Schwarze, A. Gupta, T. Hickel, R. Darvishi Kamachali.
We investigate the evolution of large number of δ′ coherent precipitates from a supersaturated Al-8 at.% Li alloy using large-scale phase-field simulations. A chemomechanical cross-coupling between mechanical relaxation and diffusion is taken into account by considering the dependence of elastic constants of the matrix phase onto the local concentration of solute atoms. The elastic constants as a function of solute concentration have been obtained using density functional theory calculations. As a result of the coupling, inverse ripening has been observed where the smaller precipitates grow at the expense of the larger ones. This is due to size-dependent concentration gradients existing around the precipitates. At the same time, precipitates rearrange themselves as a consequence of minimization of the total elastic energy of the system. It is found that the anisotropy of the chemomechanical coupling leads to the formation of new patterns of elasticity in the matrix thereby resulting in new alignments of the precipitates.
The bilateral chemomechanical coupling results is stabilization of precipitates and emergence of new patterns of elasticity in the system. In the Figure 2D cross-sections of 3D phase-field simulations are shown. Different coupling values lead to different alignment of precipitates (green arrows).