Nan Li
Center for Integrated Nanotechnologies
Los Alamos National Laboratory

Thermal and Mechanical Stability of Nanotwinned Cu

Location: EB1 Room 1011

Tuesday, January 13th 2015 - 3:45 pm

Nanotwinned metals (such as Cu, Ag) are attractive in many applications because they achieve high strength and high ductility while retaining the high electrical conductivity of a pure metal. The extremely high strength is due to the fact that coherent twin boundaries can effectively inhibit dislocation motion. According to the classification of their origin, twin morphology can be brought into materials through synthesis, thermal annealing or mechanical deformation. Before contributing to the industrial application, the stability of nanotwin structure deserves to be considered. In this talk, nanotwinned Cu has been synthesized by magnetron sputtering technique. The evolution of morphology and mechanical properties has been explored through high temperature annealing and room temperature mechanical rolling. Afterwards, morphology of nanotwin and high strength is well retained. And an interesting phenomenon has been revealed in both scenarios: the annihilation of very thin twins (twin thickness ~ 2nm). In order to understand the de-twinning mechanism, in situ indentation has been performed in a transmission electron microscope (TEM). We discover that de-twinning is a consequence of the migration of incoherent twin boundary (ITB) and corresponding migration behavior is directly connected with local dislocation structure. Meanwhile, the phenomenon of twinning dislocation multiplication at coherent twin boundary (CTB) has been explored. These studies provide insight on the design of nanotwinned metals. The work is funded by DOE, BES.

Nan Li earned his doctoral degree from the Department of Mechanical Engineering at Texas A&M University, College Station in 2010. After graduation, he joined Los Alamos National Laboratory as a post-doctoral researcher from 2010 to 2013. Since Feb. 2013, he has been a staff scientist in the Center for Integrated Nanotechnologies, LANL. His current research aims, through in situ SEM/TEM, to explore our understanding of how atomic structures of interfaces contribute to the evolution of deformation-induced or radiation-induced defects and damage in advanced materials. And using this knowledge, he aspires to develop design principles for nanocomposite materials with tailored response at irradiation and mechanical extremes. He has authored over 30 peer-reviewed publications, two of which were listed in the ScienceDirect TOP25 Hottest Articles in Materials Science. And because of his competent leadership, he has been awarded TMS Best Graduate Student Paper Award in 2009, ACTA Student Award in 2010, LANL Distinguished Postdoctoral Performance Award in 2011 and TMS Young Leader Professional Development Award in 2014.

North Carolina State University