Stable nanofacets in [111] tilt grain boundaries of face-centered cubic metals

Abstract

Grain boundaries can dissociate into facets if that reduces their excess energy. This, however, introduces line defects at the facet junctions, which present a driving force to grow the facets in order to reduce the total number of junctions and thus the system's energy. Often, micrometer-sized facet lengths are observed and facet growth only arrests for kinetic reasons. So far, energetically stable, finite-sized facets have not been observed, even though theoretical stability conditions have already been proposed. Here, we show a case where nanometer-sized facets are indeed stable compared to longer facets in [111¯] tilt grain boundaries in Cu by atomistic simulation and transmission electron microscopy. The facet junctions lack a Burgers vector component, which is unusual, but which removes the main energy cost of facet junctions. Only attractive interactions via line forces remain, which result from a discontinuity of grain boundary excess stress at the junction. Atomistic simulations predict that the same phenomenon also occurs in at least Al and Ag. Published by the American Physical Society 2024