From Northwestern University Center for Atom-Probe Tomography
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Dr. Roy Benedek
Argonne National Laboratory
Building 223, Room B201
Argonne, IL 60439, USA
Email: benedek at anl.gov
Simulations are being performed of the atomic structure and other physical properties of ceramic/metal interfaces of interest. Particular attention is being given to interfaces that are of technological importance, and also are amenable to observation by 3d-atom-probe field-ion-microscopy, high-resolution electron microscopy, and spatially resolved electron energy loss spectroscopy. Our calculations employ both first-principles methods, based on local density functional theory, and classical molecular dynamics, using model interatomic potentials. The first-principles calculations primarily utilize plane-wave pseudopotential methods, for which efficient and scalable parallel codes are available. In the classical simulations, we employ the modified embedded atom method (MEAM) and perhaps other environmentally dependent potential formulations.
A realistic treatment of ceramic/metal interfaces must account for the lattice constant mismatch at the interface, which typically results in networks of misfit dislocations. The unit cell of the dislocation networks varies inversely with the misfit parameter. For interfaces, such as MgO/Cu, with very large misfit, the network unit cell was small enough to allow the application of first principles methods (1,2). To treat interfaces with smaller misfit, first principles calculations are restricted to the coherent-interface approximation, whereas explicit treatment of the misfit requires more approximate methods. We have recently been investigating the application of the modified embedded atom method to the model interface alumina/Nb. The parameters are being fitted to results of first-principles calculations. Another interface being studied at present is that between carbide precipitates and a TiAl matrix, a system of interest for high-temperature alloy development.