Journal
ACTA MATERIALIA
Volume 59, Issue 13, Pages 5103-5115Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2011.04.042
Keywords
X-ray diffraction; High-cycle fatigue; Finite-element analysis; Nickel alloys
Funding
- AFOSR [FA9550-05-1-0416]
- US Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-AC02-06CH11357]
- US Department of Energy [DEFG02-06ER46273]
- National Natural Science Foundation of China [11002020]
- Program for New Century Excellent Talents in University
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Fatigue crack propagation in single-crystal nickel-base superalloys was studied in situ with synchrotron X-ray imaging in a very high-cycle regime. Experiments were performed at ambient temperature with a newly developed portable ultrasonic fatigue instrument. The fatigue apparatus produced stable fatigue crack propagation with positive mean stresses for specimens as thin as 150 mu m at a loading frequency of 20 kHz. Fatigue cracks propagated in a mixed-mode crystallographic manner along {1 1 1} slip planes. Phase-contrast imaging permitted analysis of the interaction of the crack front with microstructural features. Three-dimensional linear elastic finite-element analyses were performed to investigate the driving forces for crack propagation in the sheet specimen geometry. For the experimental conditions examined, fatigue crack growth is driven by the resolved shear and normal stresses on the active crack tip slip systems. An octahedral stress intensity is proposed as the relevant driving force for crack growth which determines the fatigue crack growth plane in nickel-base single crystals at room temperature. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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