How does grain boundary energy affect diffusion and recrystallization?

• A. Boundaries act as barriers to diffusion and suppress recrystallization.
• B. Boundaries do not affect diffusion or nucleation during recrystallization.
• C. Grain boundaries can serve as fast diffusion paths for certain species.
• D. Grain boundaries do not influence defect energy.

Answer: (C)

Grain boundaries are regions where the crystal is disordered and contains extra free volume, so diffusion along these boundaries is easier than through the perfect lattice. This makes grain boundaries act as fast diffusion paths for certain species, allowing atoms and vacancies to migrate quickly along the boundary compared to the bulk. That enhanced mobility plays a big role in recrystallization, because atoms can rearrange along boundaries more readily, aiding nucleation and growth of new grains, especially where there is stored strain energy. So the correct idea is that grain boundaries provide fast diffusion pathways and influence recrystallization by enabling easier atom movement and nucleation at those interfaces. Boundaries are not simply barriers, and they do affect defect energy and diffusion, so the other statements don’t fit.