G.s. Rohrer and C.-s. Kim.: the Influence of Singular Surfaces and Morphological Changes on Coarsening the Influence of Singular Surfaces and Morphological Changes on Coarsening

Gregory S. Rohrer and Chang-Soo Kim Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA The Influence of Singular Surfaces and Morphological Changes on Coarsening When the interface energy between coarsening crystals and an intervening phase is anisotropic, mechanisms that do not affect isotropic systems become important. If there are singular surfaces, then growth and dissolution must occur by the lateral motion of steps, formed at a defect center or by two-dimensional nucleation. Here, it is shown that two-dimensional nucleation is not plausible under typical experimental conditions and that persistent step creating defects are required for a singular surface to advance or retract during coarsening. The simultaneous presence of crystals with and without defects leads to two populations that grow at very different rates and this provides an explanation for abnormal coarsening. The influence of extrinsic morphological changes is also considered. It is assumed that when relatively high energy, non-equilibrium shapes in the starting materials evolve during coarsening to shapes increasingly bound by lower energy surfaces, the mean surface energy is reduced. Simulations show that under these conditions, non-classical coarsening kinetics arise in which the rate constant decreases linearly with the mean surface energy.