Interface Facets in Systems with Large Lattice Misfit

Well-defined facets of precipitates are often considered to have a coherent or semicoherent structure, but usually no coherent region(s) can be sustained if the precipitates have a significantly larger unit cell than that of the matrix. In this work, facets in systems with large lattice misfit are described with a CS-coherent structure (CS = coincidence site(s)). Two conditions are required to form such a structure in a facet: existence of dense CS at least locally and singularity in the secondary dislocation structure if secondary misfit exists. Satisfaction of both conditions in a rational crystal plane yields a rational facet and otherwise an irrational facet. Guidelines are provided to derive geometry of potential facets according to these conditions, with applications to different precipitation systems. The CS-structures are compared with semicoherent and incoherent structures in terms of ratio of near coincidence site in the structure. Migration of different facets is discussed.