University of Minnesota
Aerospace Engineering and Mechanics
Fall 1999 Seminar Series
Semicoherent Interfaces in Crystals
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
Refreshments served after the seminar in
227 Akerman Hall.
Disability accomodations provided upon request.
Contact Kristal Belisle, Senior