Graduate Research Assistant, University of Alabama
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“The influence of alloying in stabilizing a faceted grain boundary structure”
Grain boundary structures have long been known to depend on factors such as solutes and temperature. In this work, in-situ atomic scale imaging was used to observe the faceting of a Sigma 21a [1 1 1]-tilt-axis boundary at 600 degrees Celsius and 800 degrees Celsius in a Pt-5Au (at. %) nanocrystalline alloy. With an increase in temperature, we observe an evolution from many, shorter facets to fewer, longer facets. The preferred facets are shown to be symmetrically equivalent tilt boundaries, via the fundamental zone formalism. Simulation of Pt bicrystals reveals that these preferred facets do not lie in an energy minimum (of the tilt boundaries that the grain boundary misorientation could access); however, calculation of the segregation enthalpy of Au to these grain boundary lattice sites indicates a greater preference of Au, reducing the grain boundary energy, and explaining the facet stabilization observed.