Why do dislocations assemble into interfaces in epitaxy as well as in crystal plasticity? To minimize free energy

Dislocations commonly form planar arrays that minimize the free interfacial energy between relatively mismatched crystal volumes. In epitaxy and phase transformations, the causative misfit is that between differences in lattice structure and/or orientations of different phases. In deformed homogeneous crystalline materials, the planar dislocation arrays are grain and mosaic block boundaries that accommodate relative misorientations within the same crystal structure. Thus, overwhelmingly, planar dislocation arrays have a basically common origin, namely minimization of interfacial energies. Consequently, they are all subject to the low-energy dislocation structures (LEDS) hypothesis. While the specific applications of the underlying general theory are well advanced in terms of epitaxy, phase, and grain boundaries, in connection with plastic deformation that very basis is widely overlooked, if not denied. The present article aims to (a) document the fact that, while being formed, dislocation structures due to plastic deformation are in thermodynamical equilibrium, (b) firmly establish the outlined connection between planar dislocation arrays of all types, and, thereby, (c) establish the kinship between epitaxy and plastic deformation of crystalline materials. This article is based on a presentation in the symposium “Interfacial Dislocations: Symposium in Honor of J.H. van der Merwe on the 50th Anniversary of His Discovery,” as part of the 2000 TMS Fall Meeting, October 11–12, 2000, in St. Louis, Missouri, sponsored under the auspices of ASM International, Materials Science Critical Technology Sector, Structures.