The Influence of Interfacial Atomic Structure and Nanoscale Damage Gradients on Multiscale Mechanical Behavior
  • 1:25pm Nov. 8, 2016
  • B-75 Amundson Hall
  • Nathan Mara
  • Institute for Materials Science and Center for Integrated Nanotechnologies
  • Los Alamos National Laboratory

Richard Feynman in his famous 1959 lecture described the potential for atomic-scale manipulation of matter and the fantastic control over material performance that could result. Today, this potential has been realized through advancements in materials synthesis, simulation, characterization, and property measurement. In this vein, I will present one recent example where atomic scale defect/interface interactions profoundly influence the mechanical performance of nanocomposite material, followed by a novel methodology for mechanically probing nanoscale damage gradients. 1.) Damage-tolerant bulk nanolayered composites produced via Severe Plastic Deformation. As a result of their high interface content and atomic level interfacial structure, these materials exhibit an order of magnitude increase in strength, rolling deformation to large strains, greater thermal stability, and enhanced radiation damage resistance in comparison to their coarse-grained counterparts. Bulk Cu-Nb nanolayered composites are processed from 1 mm thick polycrystalline sheets down to individual layer thicknesses of 10 nm using Accumulative Roll Bonding. This Advanced Manufacturing technique has the advantage of producing bulk quantities (kilograms) of nanocomposite material, and results in rolling textures, interfacial defect structures, and deformation mechanisms very different from those seen in nanolayered composites grown via Physical Vapor Deposition methods. Mechanical behavior as evaluated via micropillar compression, and bulk tension/compression will be discussed in terms of the effects of interfacial structure on deformation processes at diminishing length scales. 2.) Spherical Nanoindentation stress-strain mechanical measurement of nanoscale damage gradients. Nanomechanical testing is ideally suited for mechanically probing the effects of ion irradiation since ion beam damage is typically limited to within ~1 μm of the surface of the irradiated material, making bulk mechanical testing impossible. The stress-strain response of tungsten containing different damage gradients (He, W, W+He ion irradiation) reveals the effects of radiation damage on elastic deformation, the elasto-plastic transition, and strain hardening/softening behavior under spherical indentation conditions.

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