Paulo Branicio (University of Southern California) – Mechanical Behavior of Nanostructured Metallic Glasses

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Abstract

Nanostructured metallic glasses (MG), including nanoglasses (NG), nanolaminate composites, and gradient NG have the potential to considerably increase the ductility of traditional MG while preserving their outstanding mechanical properties. Results for CuxZr1-x NG thin films reveal a change in deformation mode from shear band propagation to homogeneous flow on grain size reduction with a composition dependent threshold grain size in the 3-5 nm range. NG nanopillars surprisingly display necking at all grain sizes considered. The improvement of ductility in NG comes at the price of reduced strength. However, a partial compromise is obtained using a NG with a bimodal grain size distribution which indicates an improvement in the strength without sacrificing the desired extended ductility of small grain size NG. An even better compromise of strength and ductility is achieved in composite nanolaminates combining alternating layers of MG and a small grain sized NG. An alternative promising new design consists of a seamless gradient NG combining grains from 3 to 15nm. Results from tensile loading perpendicular to the gradient direction indicates an overall significant delocalization of plasticity throughout the sample. A superior combination of strength and ductility for gradient NG is found for designs with a hard core (large grain size) compare with gradient NG with a soft core (small grain sizes), in agreement with reports for gradient nanocrystalline systems. The modeling results are in excellent agreement with experimental data and highlight the significant enhancement of plasticity induced with the use of NG architectures and points out to exciting novel applications of these materials.

Biography

Paulo Branicio is currently an assistant professor at the University of Southern California (www.usc.edu) where he runs the Branicio Research Lab (branicio.usc.edu). He obtained his Ph.D. in Physics from the Federal University of São Carlos (UFSCar), São Carlos, Brazil. He was a Postdoc researcher at the Louisiana State University (LSU), and the University of Southern California, USA. During 2008-2016 he was an IHPC Independent Investigator, Scientist and Senior Scientist at the Institute of High Performance Computing (IHPC) – A*STAR, Singapore. In 2017, he joined USC as an Assistant Professor of Chemical Engineering and Materials Science. Paulo has co-authored over 70 peer-reviewed publications. His research interests include molecular dynamics simulations of metals and ceramics under extreme conditions, nanostructured high strength ceramics, metallic glasses, phase change materials for data storage, and scalable parallel algorithms for data mining and structure analysis. He is a member of the editorial board of Scientific Reports.