Form of critical nuclei at homo-phase boundaries

Even though more than six decades have passed since the first theory on heterogeneous nucleation at grain boundaries (GBs) was established in the 1950s, the concurrent shape variation (co-deformation) of both the nucleus and the GB was still not captured by existing models. By using a fully variational approach, we demonstrate for the first time that a nucleus with low-energy facet(s) is highly deformable in response to its interaction with the GB along the triple junction line and, consequently, its energy of formation can be reduced by orders of magnitude relative to predictions by previous methods. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.