University of Minnesota
Aerospace Engineering and Mechanics
Fall 1999 Seminar Series



Semicoherent Interfaces in Crystals


Prof. Perry Leo

Department of Aerospace Engineering and Mechanics, University of Minnesota


Abstract


The problem of the loss of lattice coherence at crystal-crystal interfaces is of fundamental importance in problems ranging from the electrical properties and morphologies of thin films to the strength and fracture toughness of metal and ceramic alloys and composites. Experimental observations of crystal-crystal interfaces show that coherent interfaces eventually break down through the acquisition of misfit dislocation structures. In this talk, a continuum model for the loss of coherence and the formation of noncoherent interfaces is described. Coherence is defined by a special two-dimensional tensor field on the interface. The interfacial energy depends on this tensor in such a way that the total energy of the two-phase system may be lowered by allowing the interface to separate into coherent regions and defect regions, where the defects compensate for the mismatch between the two planes. Calculations are shown for a face centered cubic (FCC)/body centered cubic (BCC) system to illustrate the progressive loss of coherence of a given interface, and also to predict the best fitting interfaces among all possibilities.

Friday, November 19, 1999
209 Akerman Hall
2:30-3:30 p.m.


Refreshments served after the seminar in 227 Akerman Hall.
Disability accomodations provided upon request.
Contact Kristal Belisle, Senior Secretary, 625-8000.