Ex and in situ investigations on the role of persistent slip bands and grain boundaries in fatigue crack initiation

Polycrystalline copper (99.9%) was fatigued at a total strain amplitude of 0.1 and 0.2%, respectively. The tests were performed in situ under vacuum in a Large Chamber-Scanning Electron Microscope. By a repeated combination of in situ fatigue testing and ex situ focused ion beam milling, a deep insi...

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Bibliographic Details
Published in:Journal of materials research 2017-12, Vol.32 (23), p.4276-4286
Main Authors: Höppel, Heinz Werner, Goik, Philip, Krechel, Christian, Göken, Mathias
Format: Article
Language:English
Subjects:
Applied and Technical Physics
Biomaterials
Clustering
Copper
Crack initiation
Crack propagation
Edge dislocations
Editors
Extrusion
Fatigue failure
Fatigue tests
Fracture mechanics
Grain boundaries
Inorganic Chemistry
Interfaces
Investigations
Localization
Materials Engineering
Materials fatigue
Materials research
Materials Science
Metal fatigue
Nanotechnology
Plastic pollution
Point defects
Review
Single crystals
Slip
Strain
Stresses
Studies
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Summary:Polycrystalline copper (99.9%) was fatigued at a total strain amplitude of 0.1 and 0.2%, respectively. The tests were performed in situ under vacuum in a Large Chamber-Scanning Electron Microscope. By a repeated combination of in situ fatigue testing and ex situ focused ion beam milling, a deep insight into the mechanism of fatigue crack initiation and early stages of crack initiation at persistent slip bands (PSBs) and their interaction with grain boundaries was obtained. The EBSD-technique showed early slip activation and the exclusive formation of extrusions in favorably oriented grains until a certain extrusion height was reached. At the total strain amplitude of 0.2%, extrusions are formed not only in favorably oriented grains but also in grains with a lower Schmid factor due to high compatibility stresses at the grain boundaries. Extrusion growth through grain boundaries is affected by the orientation of the primary slip systems in the neighboring grains and the additional anisotropy stresses. It is concluded that early stages of crack initiation are the consequence of the formation of extrusions at PSBs in combination with the clustering of vacancies along the PSB boundaries, as it was proposed by the well-known Essmann–Gösele–Mughrabi model.
ISSN:0884-2914
2044-5326
DOI:10.1557/jmr.2017.313