Thermal relaxation of initially fractal grain boundaries

The concept of fractal geometry is used to describe serrated and rugged grain boundaries in the pure materials Zinc and Titanium after deformation and heat treatment. The fractal dimension of the grain boundaries are determined by application of optical and scanning electron microscopy over a wide range of magnifications. Measurements of the coarsening kinetics of the initially fractal-like grain boundaries during isochronous as well as isothermal annealing are presented. The results of the annealing experiments can be explained by an analytic fractal coarsening model yielding the observed dependency of the time law of grain boundary smoothing on the initially fractal dimension of the grain boundaries. The results are supported by a Monte Carlo simulation of the smoothing process of single initially fractal grains.