Diffusion induced grain boundary migration (DIGM): an atomistic simulation study

Diffusion-induced grain boundary migration (DIGM) is the phenomenon of normal grain boundary (GB) migration caused by the lateral diffusion of solutes along with it. Despite its technological importance and the fact that DIGM was first observed and studied since 1970, many aspects are still not fully understood. In this study, molecular dynamics (MD) simulations are used to investigate the physical origins of DIGM with a particular focus on the effects of solute-GB interactions. For this purpose, a few binary alloy systems are deliberately selected, e.g., Al-Ti, Al-Ni, and Ni-Cu, in which strong solute-GB interactions, including solute segregation and anti-segregation, occur. The simulation results show that strong solute segregation and anti-segregation can both influence DIGM. Furthermore, it is shown that the direction of the GB migration dramatically depends on the type of solute-GB interaction, e.g., segregation or anti-segregation, which cause attraction or repulsion between the GB and solute atoms, respectively. It is thus proven that solute-GB interactions play an important role in driving DIGM. Additionally, the driving forces for DIGM can be quantified by combining two atomistic simulation techniques, i.e., the synthetic driving force (SDF) and interface random walk methods. The second part of the study shows that such a solute-induced driving force can be tuned in both type (i.e. attraction or repulsion) and their magnitude by using different solute types (with varying atomic sizes and cohesive energy). These solute types interact with the GB differently, resulting in solute segregation or anti-segregation. Moreover, it is also found that the lattice strain resulting from atomic size mismatch, which has been proposed as an essential driving force for DIGM, is not always needed to induce GB migration. It is also proposed that the non-equilibrium distribution of solute atoms across GB (e.g., one grain being more enriched with solute atoms than the second gr