Journal
JOURNAL OF MATERIALS RESEARCH
Volume 31, Issue 6, Pages 740-752Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1557/jmr.2016.66
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Funding
- United States Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering
- United States Department of Energy's National Nuclear Security Administration [DE-AC04-94AL85000]
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Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni-40 wt% Fe containing both intrinsic and extrinsic defects were tested in tension-tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zones underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. The onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.
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