Ag segregation induced nano-facet formation at an asymmetric Cu grain boundary
Nicolas J. Peter, Max-Planck Institut für Eisenforschung, Düsseldorf, GermanyTimofey Frolov, Lawrence Livermore National Lab, Livermore, USAMaria J. Duarte , Max-Planck Institut für Eisenforschung, Düsseldorf, GermanyRaheleh Hadian, Max-Planck Institut für Eisenforschung, Düsseldorf, GermanyColin Ophus, National Center for Electron Microscopy, Berkeley , USAChristoph Kirchlechner, Max-Planck Institut für Eisenforschung, Düsseldorf, GermanyChristian H. Liebscher, Max-Planck Institut für Eisenforschung, Düsseldorf, GermanyGerhard Dehm, Max-Planck Institut für Eisenforschung, Düsseldorf, Germany
Recent diffusion experiments of Ag in Cu indicated a grain boundary transition at elevated temperatures by changing grain boundary diffusivity. Such transitions were found afterwards in molecular dynamic simulations as well, but remained experimentally to be proven. In the present contribution we present first experimental studies of such a Cu-Ag system and found a chemically triggered nano-faceting transition upon Ag segregation. In particular, the segregation of Ag to an asymmetric tilt grain boundary in Cu is investigated. Aberration-corrected scanning electron microscopy reveals that annealing a Cu bicrystal results in the formation of nanometer-sized facets composed of preferentially Ag-segregated symmetric 5 {210} segments and Ag-depleted {230}/{100} asymmetric segments. Atomistic simulations confirm the nano-facet formation observed in the experiment and demonstrate a concurrent grain boundary phase transition induced by the anisotropic segregation of Ag. Additionally, asymmetric grain boundary facet segments were found to be beneficial for Ag uptake at low solute atom concentrations. Chemical information on the Ag column occupation of single atomic columns at the grain boundary was extracted by the evolution of peak intensity ratios of scanning transmission electron microscopy images and compared to idealized image simulations. Besides the high spatial resolution achieved in aberration-corrected scanning transmission microscopy, beam-induced dynamic effects have to be considered for quantitative chemical characterization on the level of single atomic columns. By investigating the influence of beam-induced atomic Ag migration in the symmetric facet segments, we were able to extract atomic column occupancy and Ag migration paths as indicator of facet segment stability.