Michel W. Barsoum
Department of Materials Science and Engineering
Ripplocations: A New Micromechanism in the Deformation of Layered Solids
Location: EB1 Room 1011
Friday, December 2nd 2016 - 11:00 am
Plastically anisotropic/layered solids are ubiquitous in nature and understanding how they deform is crucial in geology, nuclear engineering, microelectronics, among many other fields. It has long been assumed that basal dislocations are the operative micromechanism occurring during the deformation of layered solids. Recently, however, a new defect termed a ripplocation - best described as an atomic scale ripple - was proposed to explain deformation in two-dimensional solids. In this talk I will leverage atomistic simulations of graphite to extend the ripplocation idea to bulk layered solids, and confirm that it is essentially a buckling phenomenon. In contrast to dislocations, bulk ripplocations have no Burgers vectors or polarities. In graphite, ripplocations are attracted to vacancies and other ripplocations, both within the same, and on adjacent layers, the latter resulting in kink boundaries. The latter form spontaneously when loaded. Furthermore, we present direct transmission electron microscopy evidence for bulk ripplocations in Ti3SiC2, a layered carbide. The nucleation of delamination cracks, when atomic layers are loaded edge-on with, say, a spherical indenter, is one unambiguous signature of ripplocations. Ripplocations are not only a fundamentally new deformation micromechanism in the deformation of solids, but are a topological imperative, since it is the only way atomic layers can glide relative to each other without breaking the all important in-plane bonds. A more complete understanding of their mechanics and behavior is critically important, and could profoundly influence our current understanding of how graphite, layered silicates - important in geology - the MAX phases, and many other plastically anisotropic/layered solids, deform and accommodate strain.
Prof. Michel W. Barsoum - Distinguished Professor in the Department of Materials Science and Engineering at Drexel University, Philadelphia - is an internationally recognized leader in the area of MAX phases. He is the author of two entries on the MAX phases in the Encyclopedia of Materials Science, and the book, MAX Phases, published in 2013. He is also the author of Fundamentals of Ceramics, a leading textbook in his field. In 2011, he and Drexel colleagues selectively etched the A-group layers from the MAX phases to produce an entirely new family of 2D solids - they labeled MXenes - that have sparked global interest because of their potential in many applications, least of which is energy storage. With over 350 refereed publications, and an ISI h index of 65, his work has been highly cited. He is a fellow of the American Ceramic Society and the World Academy of Ceramics. In 2000 he was awarded a Humboldt-Max Planck Research Award for Senior US Research Scientists. Since 2008 he has been a visiting professor at Linkoping University in Sweden. He spent his last sabbatical year at Imperial College in London and the Grenoble Institute of Technology in Grenoble, France.