Molecular dynamics simulations of high-energy twist and tilt bicrystals in this face-centered cubic material revealed a universal liquid-like isotropic high-temperature diffusion mechanism which was characterized by a relatively low self-diffusion activation energy. The latter was independent of the boundary type or misorientation. Medium-energy grain boundaries exhibited the same behavior at the highest temperatures. At lower temperatures, the diffusion mechanism became anisotropic, with a higher misorientation-dependent activation energy. The simulations demonstrated that the lower activation energy at high temperatures was caused by a structural transition; from a solid boundary structure at low temperatures, to a liquid-like structure at high temperatures. It was demonstrated that the existence of such a transition was important for diffusion creep in nanocrystalline face-centered cubic metals. The simulations revealed that, in the absence of grain growth, nanocrystalline microstructures which contained only high-energy grain boundaries exhibited steady-state diffusion creep. The creep rate agreed quantitatively with that given by the Coble-creep formula. The activation energy for high-temperature creep was the same as that which characterized the universal high-temperature diffusion in high-energy bicrystalline grain boundaries.

Effect of High-Temperature Structure and Diffusion on Grain-Boundary Diffusion Creep in FCC Metals. P.Keblinski, V.Yamakov: Interface Science, 2003, 11[1], 111-20