Journal
ACTA MATERIALIA
Volume 58, Issue 14, Pages 4772-4782Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2010.05.013
Keywords
Nanocrystalline materials; Plastic deformation; Yield phenomena; Microstructural heterogeneity; Thin films
Funding
- National Science Foundation [NSF ECS-0304243, NSF CMMI-0728189]
- Materials Science Functional Materials and Nanostructures
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In situ transmission electron microscopy straining experiments with concurrent macroscopic stress-strain measurements were performed to study the effect of microstructural heterogeneity on the deformation behavior of nanocrystalline metal films. In microstructurally heterogeneous gold films (mean grain size d(m) = 70 nm) comprising randomly oriented grains, dislocation activity is confined to relatively larger grains, with smaller grains deforming elastically, even at applied strains approaching 1.2%. This extended microplasticity leads to build-up of internal stresses, inducing a large Bauschinger effect during unloading. Microstructurally heterogeneous aluminum films (d(m) = 140 nm) also show similar behavior. In contrast, microstructurally homogeneous aluminum films comprising mainly two grain families, both favorably oriented for dislocation glide, show limited microplastic deformation and minimal Bauschinger effect despite having a comparable mean grain size (d(m) = 120 nm). A simple model is proposed to describe these observations. Overall, our results emphasize the need to consider both microstructural size and heterogeneity in modeling the mechanical behavior of nanocrystalline metals. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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