Journal
ACTA MATERIALIA
Volume 143, Issue -, Pages 77-87Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2017.10.004
Keywords
Crack growth; In situ TEM; Nanocrystalline films
Funding
- NSF through CAREER award [DMR-1255046]
- project NEXT of the Programme des Investissements d'Avenir [ANR-10-LABX-0037]
- project MIMETIS of the Programme des Investissements d'Avenir [ANR-10-EQPX-38-01]
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This study investigated the combined effects of thickness (30 vs 100 nm) and average grain size (40 vs 70 nm for the thicker films) on the crack propagation mechanisms in ultrathin nanocrystalline gold microbeams, using a microelectromechanical system device to perform in situ transmission electron microscope (TEM) tensile experiments. Monotonic tensile tests of the two types of microbeams show similar strength levels (similar to 400 MPa) and ductility (similar to 2%). However, the thicker specimens exhibit a much more ductile behavior under repeated stress relaxation experiments, which the in situ TEM experiments revealed to be related to differences in intergranular crack propagation mechanisms. The governing crack growth process is in both cases dominated by grain boundary dislocation activities leading to grain boundary sliding. For the thinner specimens, secondary nanocracks are generated (as a result of grain boundary sliding) ahead of the main crack and coalesce together. Instead, secondary nanocracks do not form ahead of the main crack for the thicker specimens; the main crack extends as a result of sustained grain boundary sliding at the crack tip. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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