Title:

Bulk Nanolamellar Composites and their Microstructural Response to Extreme Plastic Strains

Speaker:

Dr. Nathan Mara

Affiliation:

Los Alamos National Laboratory

When:

Thursday, December 8, 2011 at 3:00:00 PM   Add to Calendar

Where:

Love Building, Room 109

Host:

Antonia Antoniou
antonia.antoniou@me.gatech.edu
404-894-6871

Abstract

Nanolayered Cu-Nb composites with layer thicknesses less than 100 nm exhibit enhanced material properties such as ultra-high strength, high ductility, and radiation damage resistance. At such fine length scales, the atomic structure of the Cu-Nb interface plays a dominant role in its response to defects and dislocations. We utilize Accumulative Roll-Bonding (ARB) to process bulk Cu-Nb nanolamellar composites from 1 mm thick high-purity polycrystalline sheet into bulk nanocomposites with individual layer thicknesses below 100 nm. The ARB process imposes thousands of percent strain to refine the microstructure of ordinary coarse-grained composite metals down to submicron and nanoscales. TEM analysis showed that the stable ARB interface structure at layer thicknesses less than 50 nm maintains the conventional Kurdjumov-Sachs (KS) orientation, but joins the Cu and Nb crystals at interface planes different from those observed in Physical Vapor Deposited materials investigated previously: {112}Cu || {112}Nb. In addition, twin formation was experimentally observed in copper on a plane that lies 19.5 degrees from the {112} interface plane. This twin formation is unusual since it does not occur in rolled physical vapor deposited (PVD) nanolayered Cu-Nb composites, where the classical KS {111} Cu || {110} Nb is maintained at the interface. In this study, atomistic simulation and electron microscopy is used to explore the interface structure and intrinsic defects in a {112}KS Cu-Nb interface, and is discussed in terms of the influence of interfacial geometry and atomic structure on the propensity for deformation twinning.

Biography

Dr. Mara received his PhD from UC Davis in 2005, where his work focused on determining the structure/mechanical behavior relationships of structural nanomaterials at elevated temperatures. From 2005 to 2008, he was a Director’s Postdoctoral Fellow at the Los Alamos National Laboratory in the Center for Integrated Nanotechnologies (CINT) researching plastic flow behavior in laminar nanocomposites. Since 2008, he has been a Staff Scientist at LANL, where his research interests have evolved to include synthesis of bulk structural nanocomposites and interfacial effects on material performance at mechanical and radiation extremes. He is the nanomechanical testing subject matter expert at CINT, a DOE-BES user facility. Dr. Mara is currently the experimental project lead for the Severe Plastic Deformation team for the Center for Materials at Irradiation and Mechanical Extremes, and the experimental team lead for the LANL Laboratory Directed Research and Development project entitled “Innovative and validated sub-micron to meso-scale modeling of the evolution of interface structure and properties under extreme strains”. In this position, he leads small teams (~12 researchers) of students, postdocs, and staff and was awarded the 2010 LANL Distinguished Mentor Performance Award for his work. The current work was funded by the Department of Energy, Office of Science, Basic Energy sciences, and the LANL LDRD office.

Notes

Meet the speaker