Michael Chandross, Material Physical and Chemical Sciences Center, Sandia National Laboratories, Albuquerque NM
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Abstract: The friction between bare sliding metals is a direct result of the atomic-scale deformation mechanisms active in the materials. While friction in metals is usually high, previous work has demonstrated that low friction in metallic contacts can occur, and that it is associated with the formation and persistence of a thin layer of ultra-nanocrystalline material (grain sizes ~10 nm) at the sliding interface. At these grain sizes, shear is no longer accommodated by dislocation motion (i.e. intragranular deformation) but rather through grain boundary sliding (intergranular deformation), often associated with inverse Hall-Petch behavior. We present a treatment of grain boundary sliding that provides qualitative and quantitative descriptions of low friction in metals. This framework -- based on materials properties with no adjustable parameters -- accurately predicts the strength of a variety of pure metals (FCC, BCC, and HCP), dilute alloys and more complex materials like high entropy alloys and metallic glasses. By directly connecting bond strengths and deformation mechanisms with the macroscale properties of metals, this work implies opportunities for optimization of alloys for low friction and high strength applications. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 (SAND2022-1056 A).
Bio:
Michael Chandross is a Distinguished Member of the Technical Staff at Sandia National Laboratories in Albuquerque, NM. He holds a B.S. in Physics with Electrical Engineering from the Massachusetts Institute of Technology (1990), and a doctorate in Physics from the University of Arizona (1996), where he studied the optical properties of conjugated polymers. After completing a National Research Foundation postdoctoral fellowship at SPAWAR Systems Center in San Diego, CA, he moved to Sandia as a postdoctoral researcher in 1999. He joined the technical staff of Sandia in 2001, where he has used large-scale simulations to study the aging and reliability of materials. At Sandia Michael has had a varied research career, including the study of adsorption of small molecules in zeolites, grain growth in polycrystalline metals, nanoimprint lithography, brazing, novel nanosolders, and tribology in systems ranging from microelectromechanical systems (MEMS) coatings to metallic contacts. Michael is a fellow of the American Physical Society, has authored close to 90 technical publications, holds three patents, and has had his work featured on the covers of the ACS journal Langmuir, the trade journal JOM from The Minerals, Metals and Materials Society, Advanced Materials, and innovation magazine.
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