Atomic structures and compositions of internal interfaces. Progress report, September 1, 1992--August 31, 1993

This research program addresses fundamental questions concerning the relations between atomic structures and compositions of homophase and heterophase interfaces. Metal/ceramic heterophase interfaces are created via the process of internal oxidation of metallic alloys. The interfaces are studied via a combination of conventional transmission electron microscopy, high resolution electron microscopy, field-ion microscopy and atom probe microscopy. The latter technique is employed to chemically sequence the interfacial region, and to show that the terminating (222) plane of MgO and CdO consists solely of oxygen atoms forthe Cu/MgO (111) and Ag/CdO (111) heterophase interfaces, respectively; this is achieved with no deconvolution of the experimental data. The evolution of metal/ceramic heterophase interfaces is studied by following the process of internal oxidation on an atomic scale from its very earliest stages. It is demonstrated that during the early stages of internal oxidation that metal atom clusters as well as hypo and hyperstoichiometric metal-oxygen clusters are present. Solute-atom segregation to grain boundaries is studied in binary metal alloys employing the free energy simulations and the overlapping distribution Monte Carlo methodologies for dilute Pt(Au), Cu(Ni) and Pd(Ni) alloys for both twist and tilt boundaries