Brown University Materials Science Research and Engineering Center

1. Brown University Materials Science Research and Engineering Center Nanotwins Deter Crack Growth William A. Curtin, Brown University, DMR 0520651 Arresting advancing cracks in structures is key to preventing catastrophic failure, and materials are often designed for this purpose by manipulating their chemistry and microstructure. A Twin is one such sub-granular microstructuralfeature intrinsic to many metals, alloys and ceramics. Recently, twins have drawn considerable attention as a means to enhance mechanical properties of metals when present in the nanometer scale. An open question is whether and how they can provide resistance to growing cracks and enhance the damage tolerance of materials. At Brown, in-situ electron microscopy experiments coupled with atomistic simulations have been used to investigate why nanotwinnedcopper can be a tough and ductile material. Experiments show that a growing crack can jump across twin layers, which then bridge the crack surfaces and restrain crack growth, leading to high fracture toughness. Atomic simulations reveal that dislocations emitted from the crack tip accumulate on the twin boundary and form a dense dislocation wall on both sides of the twin boundary, which then resists further transmission of dislocation activity across the twin boundary and confine crack nucleation by rendering the twin layers increasingly immune to plastic deformation in the crack tip field. Figure. In-situ transmission electron microscope studies and atomistic simulations of fracture in nanotwinned Cu thin film show that thin twins trap dislocations and remain as bridging ligaments behind the crack tip, leading to enhanced facture toughness of the material. Sponsored by the NSF MRSEC on “Micro-and Nano Mechanics of Materials” at Brown U., DMR 0520651.