An interface facet driven Rayleigh instability in high-aspect-ratio bimetallic nanolayered composites

One limitation hindering the structural and electrical applications of nanostructured metals is the loss of their nanostructure and strength under elevated temperatures. Nanostructured metals often have grain structures that contain a high density of triple junctions, where thermally induced instabilities commonly initiate. Prior work has resulted in fabrication of nanolayered two-phase composites that possess high-aspect ratio grains, a scarcity of triple junctions, and a thermally stable microstructure. In this work, transmission electron microscopy is used to investigate how these composites could eventually breakdown during heating. We reveal an unconventional thermal instability mechanism in this class of materials, which operates without the assistance of triple junctions. The mechanism can be rationalized by that thermally induced pinch off occurs as the result of bimetal interface faceting and can trigger a classic Rayleigh instability.