Abnormal grain growth via the migration of planar growth interfaces

Nanocrystalline nickel electrodeposits undergo a sequence of morphologically distinct grain growth stages during annealing. The nanostructure initially undergoes a rapid sequence of abnormal grain growth, followed by a much slower normal grain growth stage. Out of this uniformly growing structure comes a second stage of abnormal grain growth which not only accelerates the overall growth rate, but the transformation also occurs by the migration of planar reaction fronts. These planar growth interfaces are composed of many individual grain boundary segments, migrating together at essentially the same velocity. Grain shape was studied from intergranular fracture surfaces: it was found that the abnormally growing grains were cuboidal in shape and were present either as individually growing grains or as cuboid clusters. Electron backscatter diffraction showed numerous twin-related cuboidal grain clusters having complex compound planes. (C) 2008 Elsevier B.V. All rights reserved.