Grain boundary roughening transitions

We consider the roughening of small-angle grain boundaries consisting of arrays of dislocations and found two transitions, corresponding to fluctuations of the dislocations along and perpendicular to the boundaries. The latter contributes to a large-scale fluctuation of the orientation of the crystal but the former does not. The transition temperatures of these transitions are very different, with the latter occuring at a much higher temperature. Order-of-magnitude estimates of these temperatures are consistent with recent experimental results from elasticity and X-ray measurements in solid He-4. Copyright (C) EPLA, 2009