Effects of vacancy transport and surface adsorption on grain boundary migration in pure metals

Vacancy transport has a demonstrable impact on the microstructural evolution of polycrystalline metals, but existing models typically require knowledge of the stress state in order to describe lattice site generation and annihilation at interfaces. Using irreversible thermodynamics, the driving forces and equilibrium conditions dictating the response of incoherent interfaces are derived for a pure metal with vacancies under stress-free conditions. A phenomenological set of linear kinetic expressions that guarantees a decrease in the total energy upon diffusion is proposed. A near-equilibrium steady-state analytical solution for grain boundaries is obtained. In the stress-free limit, interface migration and transboundary diffusion are closely coupled, as are the production or annihilation of vacancies and the rigid-body dilation or contraction of the bulk grains. Solutions for various limiting kinetic regimes are also obtained, and the relevance of the kinetic parameters to pore nucleation at grain boundaries is discussed.