High-temperature structure and properties of grain boundaries: long-range vs. short-range structural effects

Recent molecular-dynamics simulations of the high-temperature structure of high-energy grain boundaries in silicon and in f.c.c. metals have revealed a universal, highly confined, liquid-like structure. As a consequence, at elevated temperatures grain-boundary properties, such as the diffusivity and mobility, involve liquid-like mechanisms and are independent of the boundary misorientation, with activation energies related to the liquid state. At lower temperatures these boundaries undergo a reversible structural and dynamical transition from a confined liquid to a more or less disordered solid. Consistent with experiments, the temperature for this transition decreases with increasing grain-boundary energy, suggesting an important role of the degree of short-range grain-boundary structural disorder in key GB properties.