Characterizing Plastic Deformation Mechanisms in Nanograined Metal Thin Films Using in Situ TEM Straining

Sandra Stangebye, Georgia Institute of Technology

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Nanocrystalline (nc) and ultrafine-grained (ufg) metal thin films show increased mechanical strength and radiation tolerance when compared to their coarse-grained equivalents. These behaviors are due to the high volume fraction of grain boundaries (GBs) that both inhibit dislocation glide (increasing strength) and absorption of radiation damage (increasing radiation tolerance). However, the active deformation mechanisms during straining are not well characterized and it is also not well understood how radiation damage may alter the deformation mechanisms. This lack in understanding limits material design towards exceptional mechanical properties, particularly when materials are subject to extreme conditions such as the combination of stress and a radiation environment. To understand this behavior, the plastic deformation kinetics of ufg and nc metal thin films have been investigated using an in situ TEM nanomechanical testing technique. This technique allows for simultaneous observation of the active deformation mechanisms and quantification in terms of stress/strain and true activation volume, which is a signature parameter associated with a deformation mechanism. Experiments have been conducted on gold (Au) and aluminum (Al) thin films (both irradiated and unirradiated) with varying thicknesses, grain sizes, and texture. A variety of deformation mechanisms have been identified, including dislocation nucleation and absorption at grain boundaries (GBs), inter- and intragranular dislocation glide, and GB migration. Experimentally measured activation volume values are compared with values determined from atomistic simulations for different unit dislocation processes to determine the most likely rate-controlling mechanism that governs deformation of these nc/ufg metal thin films.

Abstract Author(s): Sandra Stangebye, Kunqing Ding, Yin Zhang, Ting Zhu, Olivier Pierron, Josh Kacher